September 10, 2018 Weather and Climate Report – Major Hurricane Expected to Land Thursday

Written by Sig Silber

Updated at 3:00 PMM EDT September 12, 2018: A strong but delayed, rerouted and possibly weakening but wetter Florence and a weakened Isaac on track for landfall Thursday. A weakened Olivia will encounter the Hawaiian Islands today.

This is our final update of this article. A new article focused only on the cyclones will be published tonight Wednesday September 12, 2018

see much cyclonic activity and the analogs to the current conditions suggest El Nino is coming possibly as a Modoki (westerly displaced). But the Eastern Pacific Equatorial sea surface temperatures and also at depth suggest this may be a month or two away.  This Monday night Weather and Climate Report includes a full Tropical Cyclone Update and we will update that portion of the report until we go back to the short form of our Major Event Reporting probably Wednesday night so look for that article about Cyclones. Until then the information in this article will be routinely updated.

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Source: http://derecho.math.uwm.edu/models/

Tropical Update

It is useful to understand where these storms will encounter water that is warmer or cooler than normal. It may or may not be useful for determining storm tracks but it is helpful at determining where a storm is likely to get stronger or weaker but does not provide a lot of clues on wind sheer which is also very important. It is one of many things I look at so I share it with my readers. The waters around Hawaii are a bit warmer today but nevertheless, Olivia is declining rapidly. The waters off the East Coast of the U.S. are very warm and that is why Florence is intensifying rapidly. Isaac is where the water is consistent with climatology and Isaac is struggling to maintain its Hurricane Status. Water to the east of Japan is warmer than climatology and that has been a factor in that part of the World.

The below is also relevant re Florence:

First let us focus on the Atlantic and of course Florence

NHC is not confident that they can forecast the exact track of this storm. It is likely to impact the U.S. East Coast but exactly where is still not clear. M means a very strong storm.

Here is the link to the general discussion and much other information.

Here is a recent discussion.

Hurricane Florence Discussion Number  53 NWS National Hurricane Center Miami FL  AL062018 1100 AM EDT Wed Sep 12 2018

An Air Force Reserve hurricane hunter aircraft investigating  Florence this morning has found no change in the hurricane’s peak intensity of 115 kt, even though the central pressure had decreased a few millibars down to 943 mb. However, the aircraft data do indicate that Florence’s inner-core wind field has expanded, with the 50-kt wind radii now extending outward up to 100 n mi to the northeast. Florence still has a very distinct eye in satellite imagery, but cloud top temperatures have been waxing and waning in the eyewall region, with slight downward trend noted in the past hour or so. In contrast, the upper-level outflow remains impressive and continues to expand everywhere except to the south.

Florence is now moving toward the northwest or 305/13 kt. There has been no significant change to the NHC model guidance, including the corrected-consensus models HCCA and FSSE, which are now virtually on top of each other and the simple consensus model TVCA. As a result, no changes were required to the previous NHC track. The shortwave trough over the southern Plains seen in water vapor imagery could end up being a significant factor as it rounds the narrow ridge over the Tennessee Valley and is expected to erode the ridge along the U.S. mid-Atlantic coast on days 3-5. At this time, little change has been made to the NHC track forecast, which remains very close to the aforementioned consensus aids through 72 hours. On the current forecast track, the center of Florence is expected to be near the coasts of southern North Carolina and northern South Carolina in 48 to 72 hours and then drift westward to west-southwestward in weak steering flow.

There is still a narrow window of opportunity for Florence to strengthen a little when the cyclone moves over the warmest SSTs and highest upper-ocean heat content while the shear will be the lowest between 0600-1200 UTC tomorrow morning. After that, decreasing ocean heat content along with the slowing forward speed of Florence should cause at least some cold upwelling beneath the hurricane, which should induce a gradual weakening trend. Once Florence reaches the shallow coastal shelf waters in 72 h, land interaction and more significant upwelling are expected, further enhancing the weakening process. The NHC intensity forecast remains near the higher statistical guidance through 48 hours, then follows the trend of the decay SHIPS model after that time.

While Florence’s maximum winds are expected to weaken a little, it is still expected to remain a dangerous major hurricane as it approaches the coast. The threat to life from storm surge and rainfall will not diminish, and these impacts will cover a large area regardless of exactly where the center of Florence moves.

Key Messages:

1. A life-threatening storm surge is now highly likely along portions of the coastlines of South Carolina and North Carolina, and a Storm Surge Warning is in effect for a portion of this area.  All interests in these areas should complete preparations and follow any advice given by local officials.

2. Life-threatening, catastrophic flash flooding and significant river flooding is likely over portions of the Carolinas late this week into early next week, as Florence is expected to slow down as it approaches the coast and moves inland.

3. Damaging hurricane-force winds are likely along portions of the coasts of South Carolina and North Carolina, and a Hurricane Warning is in effect. Strong winds could also spread inland into portions of the Carolinas.

4. Large swells affecting Bermuda and portions of the U.S. East Coast will continue this week, resulting in life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 29.8N  71.3W  115 KT 130 MPH

 12H  13/0000Z 31.1N  73.1W  120 KT 140 MPH

 24H  13/1200Z 32.6N  75.1W  125 KT 145 MPH

 36H  14/0000Z 33.5N  76.5W  120 KT 140 MPH

 48H  14/1200Z 33.8N  77.4W  105 KT 120 MPH…NEAR THE COAST

 72H  15/1200Z 33.6N  78.4W   85 KT 100 MPH…NEAR THE COAST

 96H  16/1200Z 33.6N  80.4W   45 KT  50 MPH…INLAND

120H  17/1200Z 34.7N  82.8W   25 KT  30 MPH…INLAND

This is a graphic that shows the most reasonable time of arrival of winds.

There is also an earliest time of arrival graphic available.

Isaac

Here is a recent discussion. The next discussion will be in a new article we publish tonight September 12.

Tropical Storm Isaac Discussion Number  20 NWS National Hurricane Center Miami FL  AL092018 1100 AM AST Wed Sep 12 2018

GOES-16 1-minute satellite imagery along with NOAA Hurricane Hunter data show that the center of Isaac has become fully exposed on the northwestern side of a shrinking area of deep convection.  There is still a lot of wind there, however, with the NOAA plane observing SFMR and adjusted flight-level winds to support 50 kt as an initial intensity.

An upper-level trough is dropping southward over the central Atlantic, which has increased the shear this morning over Isaac. This high shear is forecast to remain for the next day or two, and it is possible that Isaac will degrade into a tropical wave during that time, although the area of tropical-storm-force winds will likely not go away for a while.  In a couple of days, while the wind shear could decrease over the east-central Caribbean Sea, there might not be much of a system left to take advantage of the more conducive conditions.  As a compromise, the official forecast shows a slow weakening, in the direction of the model consensus, and continues to show dissipation after 96 hours in line with the GFS/ECMWF guidance.  I wouldn’t pay much attention to the long range forecast for now, given the uncertainties in Isaac surviving during the next day or two.

The low-level center of Isaac has recently accelerated, moving westward at 15 kt, as it decoupled from the slower mid-level flow. Assuming the system stays vertically coherent, a large mid-tropospheric high is forecast to persist for the next several days.  This should keep the system moving westward at a somewhat slower pace throughout the forecast period.  There isn’t much spread in the guidance, and the official forecast is close to the previous one after accounting for the initial position.  The long-range track forecast highly depends on the intensity forecast, so it should be considered low confidence.

Key Messages:

1. Isaac is expected to remain at tropical storm intensity when it moves across the Lesser Antilles on Thursday, and tropical storm warnings are in effect for Martinique, Dominica, and Guadeloupe. Tropical storm watches are in effect for Montserrat, St. Kitts and Nevis, Antigua, and Saba and St. Eustatius.  Interests on those islands should follow any advice given by their local officials.

2. Life-threatening flash flooding is possible with Isaac.  The storm is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up 8 inches across Martinique, Dominica and Guadeloupe. Rainfall amounts of 1 to 2 inches with isolated amounts to 4 inches are expected across Puerto Rico and the southern United States Virgin Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 15.0N  54.7W   50 KT  60 MPH

 12H  13/0000Z 15.1N  56.7W   50 KT  60 MPH

 24H  13/1200Z 15.3N  59.4W   45 KT  50 MPH

 36H  14/0000Z 15.3N  62.6W   45 KT  50 MPH

 48H  14/1200Z 15.4N  65.6W   40 KT  45 MPH

 72H  15/1200Z 15.5N  71.0W   40 KT  45 MPH

 96H  16/1200Z 15.5N  75.0W   35 KT  40 MPH

120H  17/1200Z…DISSIPATED

There are more storms to come. The Gulf of Mexico looks to be the location for the next new storm. But there are other possibilities also. 

Notice the indication of something going on in the Gulf of Mexico. I have included part of todays discussion on that with the regular NOAA discussion of the 6 – 10 and 8 – 14 day forecasts.

Tropical Storm Helene

It does not look like a threat to the U.S. or Bermuda so for the time being we are not providing the discussion but of course it is available from the NHC

Gordon

Gordon has already landed but the remnant continues to have the potential to create local flooding. Coverage of this has been transferred over to the Weather Prediction Center which you can access here or by the local NWS offices in the area impacted.

And longer term:

We will very soon discontinue coverage of Gordon as it is now almost impossible to separate out those impacts from other weather factors.

Shifting focus to the Pacific

Olivia which is no longer a Hurricane

Here is a recent discussion: It may be the last we post. And any future posts will be in the new article published tonight (Wednesday September 12, 2018)

Tropical Storm Olivia Discussion Number  48 NWS Central Pacific Hurricane Center Honolulu HI   EP172018500 AM HST Wed Sep 12 2018

An explosive overnight development of thunderstorms in Olivia’s eastern semicircle have since moved over the low level circulation center (LLCC), despite westerly vertical wind shear near 25 kt. Subjective Dvorak current intensity estimates ranged from 2.0/30 kt to 2.5/35 kt this time around, but velocity data from the WSR-88D on Molokai indicate 50 kt winds at 5000 feet, and 45 kt at 10000 feet. Using reduction factors typically applied to aircraft data, this supports a surface wind estimate of 40 kt.

Olivia’s motion over the past 18 hours has been erratic, and strongly modulated by the amount of associated deep convection. A faster motion toward the west-southwest was observed when

convection dissipated yesterday, with a slower forward speed towardthe west-northwest observed with the deeper convection. This is due to the vertical wind shear, with the exposed low cloud swirl steered by low-level trade winds, while the deep convection allows Olivia’s motion to be increasingly affected by the westerly flow aloft. With the persistent overnight convective burst, the initial motion estimate for this advisory is estimated to be 280/10 kt.

In the short term, Olivia is expected to move toward the west. However, the expectation is that the deep convection will wane later this morning, and Olivia will make a turn toward the west-southwest by this afternoon. After emerging to the west of Maui County this evening, the expectation is that terrain interaction and increasing vertical wind shear will prevent deep convection from  persisting over the center. A motion toward the west-southwest is then expected through 36 hours, with the assumption that the LLCC will be intact after emerging to the southwest of Maui County. GFS guidance indicates dissipation within 48 hours, while the ECMWF carries a surface low through day 5. The official forecast splits the difference, with Olivia devolving to a post-tropical remnant low by day 3 before dissipation on day 5.

Key Messages:

1. Flooding rainfall, high surf, and damaging winds are expected in the warning area. Significant impacts can occur well away from the center, especially when considering that the mountainous terrain of Hawaii can produce localized areas of strongly enhanced wind gusts and rainfall.

FORECAST POSITIONS AND MAX WINDS

 INIT  12/1500Z 21.2N 155.7W   40 KT  45 MPH

 12H  13/0000Z 20.6N 157.6W   40 KT  45 MPH

 24H  13/1200Z 20.0N 160.4W   35 KT  40 MPH

 36H  14/0000Z 19.6N 163.1W   30 KT  35 MPH

 48H  14/1200Z 19.6N 166.0W   30 KT  35 MPH

 72H  15/1200Z 20.5N 171.5W   30 KT  35 MPH…POST-TROP/REMNT LOW

 96H  16/1200Z 21.0N 177.0W   30 KT  35 MPH…POST-TROP/REMNT LOW

120H  17/1200Z…DISSIPATED

And there is more to come

 Tropical Storm Paul previously Depression 18-E may just fade away. We will see but that is what it looks like now. Notice there is another Tropical Depression right behind it. We will know more about that probably in a day or two at most.

And the U.S. is not the only place dealing with cyclones. When we published on Monday night, Japan was about to be hit and since has been hit.

This graphic should update and shows the situation in the Western Pacific. We are now tracking two storms.

Update information can be found here.

MANGHUT

And now also Tropical Storm 27W (Barijat)

There may be more coming in both the Atlantic and the Pacific.

Below is an analysis of projected tropical hazards and benefits over an approximately two-week period.

Back to our regular format

A. We now switch to our usual summary first for temperature and then for precipitation of small images of the three short-term maps. You can click on these maps to see larger versions. The easiest way to return to this report is by using the “Back Arrow” usually found top left corner of your screen to the left of the URL Box. Larger maps are available later in the article with the discussion and analysis.

Sometimes it is useful to see the evolution of the forecasts from the 1 – 5 Day,  6 – 10 Day (which NOAA considers to be Week-1 of their intermediate forecast) , 8 – 14 Day (which NOAA considers to be Week-2) and Week 3 and 4 (which after being issued overlap with Week-2). I do not have comparable maps for the Day 1 – 5 forecast in the same format as the three maps we generally work with. What I am showing for temperature  is the Day 3 Maximum Temperature and for precipitation the five-day precipitation: the latter being fairly similar in format to the subsequent set of the maps I present each week but showing absolute QPF (inches of precipitation) not QPF deviation from Normal.

First Temperature

This shows magnitude rather than probability of  being higher or lower than Normal and shows the middle day of the five day period.	Fairly stable but de-intensifying pattern		↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 forecast depends on a renewal of the Monsoon which to me seems unlikely.

And then Precipitation

The five day QPF is shown above.The units are different than the other maps i.e. in units of precipitation (inches) not probabilities of exceeding or being less than climatology.	Perhaps a stable pattern. But  also deamplifying		↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 shown to the left like temperature is based on a resumption of the Monsoon which may not happen.

A. Now we will begin with our regular approach and focus on Alaska and CONUS (all U.S.. except Hawaii).

Water Vapor.

This view of the past 24 hours provides a lot of insight as to what is happening.

You can see from this animation that the pattern has become more zonal and the level of Monsoon Activity is greatly diminished.

Tonight, Monday September 10, 2018, as I am looking at the above graphic, the Monsoon looks to be less active and confined to Southeast Texas.

his graphic is about Atmospheric Rivers i.e. thick concentrated movements of water moisture. More explanation on Atmospheric Rivers can be found by clicking here or if you want more theoretical information by clicking here. The idea is that we have now concluded that moisture often moves via narrow but deep channels in the atmosphere (especially when the source of the moisture is over water) rather than being very spread out. This raises the potential for extreme precipitation events. You can convert this graphic into a flexible forecasting tool by clicking here. One can obtain views of different geographical areas by clicking here.

And Now the Day One and Two CONUS Forecasts

60 Hour Forecast Animation

Here is a national animation of weather fronts and precipitation forecasts with four 6-hour projections of the conditions that will apply covering the next 24 hours and a second day of two 12-hour projections the second of which is the forecast for 48 hours out and to the extent it applies for 12 hours, this animation is intended to provide coverage out to 60 hours. Beyond 60 hours, additional maps are available at links provided below. The explanation for the coding used in these maps, i.e. the full legend, can be found here although it includes some symbols that are no longer shown in the graphic because they are implemented by color coding.

You can enlarge the below daily (days 3 – 7) weather maps for CONUS by clicking on Day 3 or Day 4 or Day 5 or Day 6 or Day 7. These maps auto-update so whenever you click on them they will be forecast maps for the number of days in the future shown.

What is Behind the Forecasts? Let us try to understand what NOAA is looking at when they issue these forecasts.

Below is a graphic which highlights the forecasted surface Highs and the Lows re air pressure on Day 7. The Day 3 forecast can be found here. the Day 6 Forecast can be found here. Actually all the small graphics below can be clicked on to enlarge them.

When I look at this Day 7 forecast, we see the Hawaiian High with surface central pressure of 1028 hPa. The Aleutian Low is weak with surface central pressure of 1008 hPa and it is located in the Gulf of Alaska suggesting that we may see a West Coast trough soon after. To the north, there is an Arctic High with surface central pressure of 1024 hPa. Further east, over Greenland there is a High with surface central pressure of 1020 hPa. We can locate the Bermuda High with surface central pressure of at least 1020 hPa. It has been blocking Florence from turning north. The Four Corners High has a surface central pressure of 1016 hPa. It is fairly far north for this time of the year. There is also an inverted trough entering from Mexico with surface central pressure of 1008 hPa.

And of course we can see the remnants of Florence over the Carolinas and not moving as they are scheduled to arrive there September 12 or 13 and this is the forecast for Sept 18 (if you read this on Tuesday September 11).

I provided this write up that provides a simple explanation on the importance of semipermanent Highs and Lows and another link that discussed possible changes in the patterns of these highs and lows which could be related to a Climate Shift (cycle) in the Pacific or Global Warming. Remember this is a forecast for Day 7. It is not the current situation.

The table below showing the Day 3, Day 4, Day 5, Day 6 and Day 7 of this graphic can be useful in thinking about how the pattern of Highs and Lows is expect to move during the week.

From left to right and then down, Days 3 and 4 top row, Days 5 and 6 second row and Day 7 to the right. These are small images but you can if you want click on them and get larger images but even with the small images you can trace the evolution of the pattern. The graphics update but my commentary below does not so it is just a guide for how to read these graphics.
Things to look for in general are the position and strength of the Aleutian Low, the Hawaiian High and any troughs especially if they extend far to the south and are over water.

Looking at the current activity of the Jet Stream.  The below graphics and the above graphics are very related.

Not all weather is controlled by the Jet Stream (which is a high altitude phenomenon) but it does play a major role in steering storm systems especially in the winter The sub-Jet Stream level intensity winds shown by the vectors in this graphic are also very important in understanding the impacts north and south of the Jet Stream which is the higher-speed part of the wind circulation and is shown in gray on this map. In some cases however a Low-Pressure System becomes separated or “cut off” from the Jet Stream. In that case it’s movements may be more difficult to predict until that disturbance is again recaptured by the Jet Stream. This usually is more significant for the lower half of CONUS with the cutoff lows being further south than the Jet Stream. Some basic information on how to interpret the impact of jet streams on weather can be found here and here.  I have not provided the ability to click to get larger images as I believe the smaller  images shown are easy to read.

Current	Day 5
Right now it is primarily zonal and far north.

Putting the Jet Stream into Motion and Looking Forward a Few Days Also

To see how the pattern is projected to evolve, please click here. In addition to the shaded areas which show an interpretation of the Jet Stream, one can also see the wind vectors (arrows) at the 300 Mb level.

This longer animation shows how the jet stream is crossing the Pacific and when it reaches the U.S. West Coast is going every which way.

Click here to gain access to a very flexible computer graphic. You can adjust what is being displayed by clicking on “earth” adjusting the parameters and then clicking again on “earth” to remove the menu. Right now it is set up to show the 500 hPa wind patterns which is the main way of looking at synoptic weather patterns. This amazing graphic covers North and South America. It could be included in the Worldwide weather forecast section of this report but it is useful here re understanding the wind circulation patterns.

500 MB Mid-Atmosphere View

The map below is the mid-atmosphere 7-Day chart rather than the surface highs and lows and weather features. In some cases it provides a clearer less confusing picture as it shows only the major pressure gradients. This graphic auto-updates so when you look at it you will see NOAA’s latest thinking. The speed at which these troughs and ridges travel across the nation will determine the timing of weather impacts. This graphic auto-updates I think every six hours and it changes a lot. Thinking about clockwise movements around High Pressure Systems and counter- clockwise movements around Low Pressure Systems provides a lot of information.

Here is the whole suite of similar maps for Days 3, 4, 5, 6 and repeated for Day 7.  It is quite complicated.

Day 3 Above, 6 Below	Day 4 Above,7 Below	Day 5 Above.

Here is the seven-day cumulative precipitation forecast. More information is available here.

 Four – Week Outlook: Looking Beyond Days 1 to 5, What is the Forecast for the Following Three + Weeks?

I use “EC” in my discussions although NOAA sometimes uses “EC” (Equal Chances) and sometimes uses “N” (Normal) to pretty much indicate the same thing although “N” may be more definitive.

First – Temperature

6 – 10 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 10, 2018 was 3 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 10, 2018 was 2 out of 5).

–

Looking further out.

Now – Precipitation

6 – 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 10, 2018 was 3 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 10, 2018 was 2 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today September 10 and the Week 3 – 4 discussion issued on September 7

6-10 DAY OUTLOOK FOR SEP 16 – 20 2018

TODAY’S ENSEMBLE MEAN SOLUTIONS ARE IN FAIRLY GOOD AGREEMENT IN DEPICTING AN AMPLIFIED 500-HPA FLOW PATTERN OVER MUCH OF THE FORECAST DOMAIN. THE 0Z ECMWF ENSEMBLE MEAN AND THE 0Z/6Z GFS ENSEMBLE MEANS PREDICT A RIDGE OVER THE BERING SEA, AND A DOWNSTREAM TROUGH OVER THE WESTERN GULF OF ALASKA. THE 0Z CANADIAN ENSEMBLE MEAN FORECASTS ZONAL FLOW THROUGH MOST OF THE SAME AREA. ALL FOUR  ENSEMBLE MEANS DEPICT A TROUGH NEAR THE U.S. WEST COAST, A SUBTROPICAL RIDGE OVER THE NATION’S MIDSECTION, AND A TROUGH EITHER NEAR OR OFF THE SOUTHEAST COAST. FOR THE LOWER 48 STATES, ENSEMBLE SPREAD (5820 M CONTOURS) IS CONSIDERED MODERATE TO HIGH WITH TROUGHS PREDICTED NEAR BOTH COASTS, WITH SPREAD REACHING A MINIMUM OVER THE NATION’S MIDSECTION. AS OF 12 NOON ATLANTIC STANDARD TIME TODAY (SEP 10) MAJOR HURRICANE FLORENCE IS NOW A CATEGORY-4 SYSTEM ON THE SAFFIR-SIMPSON HURRICANE WIND SCALE, WITH PEAK SUSTAINED WINDS OF 130 MPH. HURRICANE FLORENCE IS NOW ABOUT 1230 MILES EAST-SOUTHEAST OF CAPE FEAR, NORTH  CAROLINA, AND THE NATIONAL HURRICANE CENTER’S OFFICIAL TRACK TAKES FLORENCE ACROSS THE NORTH CAROLINA COAST ON THURSDAY. BY SATURDAY, ONE DAY PRIOR TO THE BEGINNING OF THE 6-10 DAY PERIOD, THE NATIONAL HURRICANE CENTER PREDICTS THE REMNANTS OF FLORENCE COULD BE IN THE GENERAL VICINITY OF WESTERN NORTH CAROLINA.  

THE SUBTROPICAL RIDGE FAVORS ABOVE NORMAL TEMPERATURES THROUGHOUT MUCH OF THE CONUS WITH THE HIGHEST PROBABILITIES (70%-79%) FORECAST OVER THE SOUTHWEST, AND PORTIONS OF NEW ENGLAND. THE MID-LEVEL TROUGH NEAR THE PACIFIC NORTHWEST INCREASES CHANCES OF BELOW NORMAL TEMPERATURES FROM WASHINGTON STATE TO NORTHWEST MINNESOTA, AND FROM WASHINGTON STATE SOUTHWARD TO CENTRAL CALIFORNIA. A FORECAST RIDGE AND ASSOCIATED POSITIVE HEIGHT ANOMALIES FAVOR ABOVE NORMAL TEMPERATURES OVER MUCH OF WESTERN AND SOUTHERN ALASKA. NEAR TO BELOW NORMAL TEMPERATURES ARE FAVORED OVER NORTHEAST ALASKA, ASSOCIATED WITH A COOLER AIR MASS.

ABOVE NORMAL PRECIPITATION IS FAVORED OVER MUCH OF THE CENTRAL AND EASTERN CONUS, WITH THE HIGHEST PROBABILITIES (50%-59%) DEPICTED OVER THE MID-ATLANTIC AND NORTHEAST. THESE AREAS OF PREDICTED ABOVE NORMAL PRECIPITATION ARE RELATED TO FRONTAL ACTIVITY, AND IN THE CASE OF THE EAST COAST, THE ANTICIPATED REMNANTS OF FLORENCE. BELOW NORMAL PRECIPITATION IS FAVORED IN AREAS THAT ARE FAR ENOUGH AWAY FROM FRONTAL BOUNDARIES, AND/OR NEAR/UNDER MID-LEVEL RIDGING AND POSITIVE 500-HPA HEIGHT ANOMALIES.

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 3 OUT OF 5, DUE TO FAIRLY GOOD AGREEMENT AMONG THE ENSEMBLE MEANS ON AN AMPLIFIED PATTERN OVER MUCH OF THE FORECAST DOMAIN OFFSET BY HIGH ENSEMBLE SPREAD.

8-14 DAY OUTLOOK FOR SEP 18 – 24 2018 

THE WEEK-2 CIRCULATION PATTERN IS EXPECTED TO BE FAIRLY SIMILAR TO THE PATTERN PREDICTED FOR DAYS 6-10, THOUGH WITH ONE EXCEPTION; THE FLOW OVER THE CONUS IS FORECAST TO DEAMPLIFY AND BECOME ZONAL. AS A RESULT, ABOVE NORMAL TEMPERATURES ARE FAVORED SOUTH OF THE MEAN JET, WITH NEAR TO BELOW NORMAL TEMPERATURES FAVORED ACROSS MUCH OF THE NORTHERN CONUS. NEAR TO BELOW NORMAL TEMPERATURES ARE ALSO FAVORED TO EXPAND IN COVERAGE ACROSS MUCH OF NORTHERN AND CENTRAL ALASKA. THE ANTICIPATED PRECIPITATION PATTERN IS FAIRLY WEAK, THOUGH SIMILAR TO THE 6-10 DAY PRECIPITATION OUTLOOK. ABOVE NORMAL PRECIPITATION IS FAVORED OVER  THE CENTRAL PART OF THE CONUS, AND FROM THE UPPER OHIO AND TENNESSEE VALLEYS EASTWARD TO THE ATLANTIC SEABOARD. BELOW NORMAL PRECIPITATION IS FAVORED ACROSS MOST OF THE WESTERN CONUS AND SOUTHWESTERN ALASKA. WITH THE EXPECTED APPROACH OF A MID-LEVEL TROUGH TOWARDS THE PACIFIC NORTHWEST, IT IS THOUGHT THAT ABOVE NORMAL PRECIPITATION IS A REASONABLE BET FOR THE OLYMPIC PENINSULA OF WESTERN WASHINGTON. THE FORECAST AREAS OF BELOW AND ABOVE NORMAL PRECIPITATION ARE BASED ON THE FIRST-GUESS, AUTOMATED PRECIPITATION TOOL, THE ECMWF AND GFS ENSEMBLE MEAN REFORECAST PRECIPITATION TOOLS, AND CONSIDERATION OF THE SYNOPTIC PATTERN DURING WEEK-2.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE TO RELATIVELY POOR AGREEMENT AMONG THE PRECIPITATION TOOLS ACROSS MUCH OF THE FORECAST DOMAIN.

THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON  SEPTEMBER 20.

Week 3-4 Forecast Discussion Valid Sat Sep 22 2018-Fri Oct 05 2018

ENSO-neutral conditions continue across the equatorial Pacific Ocean where sea surface temperatures (SSTs) are near-to-above average. The Madden-Julian Oscillation (MJO) has remained weak during the past month, and MJO forecasts are very uncertain over the next few weeks. Therefore, the MJO is not expected to play a major role during the Week 3-4 period. The temperature and precipitation outlooks are based on the evolving circulation pattern from Week-2, dynamical model forecasts from the NCEP CFS, ECMWF, and JMA, and the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of experimental and operational ensemble prediction systems. Long-term trends are also considered.

Positive 500-hpa height anomalies are forecast across much of the mid-latitudes of North America during Week-2, with a predicted trough and associated negative 500-hpa height anomalies over the Pacific Northwest weakening through the period. Operational and experimental dynamical models maintain broad positive 500-hpa height anomalies over much of Alaska and the CONUS for the Week 3-4 period. While there is some spread among individual model ensemble mean forecasts, a consensus of models predicts the greatest positive 500-hpa height anomalies over the central and eastern CONUS and the Gulf of Alaska.

Despite spread among the individual model height forecasts, the temperature tools are in reasonably good agreement. Models indicate increased chances for above-normal temperatures across the western U.S., from the Pacific coast eastward into the Four Corners region and the northern Plains. The highest probabilities for above-normal temperatures exceed 70% for parts of the southwestern U.S., associated with decadal climate trends. Dynamical model forecasts are in general agreement on increased chances of below-normal temperatures for parts of southeast Arizona and western Texas. Several models, including the GEFS and Canadian ensembles, indicate a larger area of increased probabilities for below-normal temperatures into the central and parts of the eastern CONUS. However, greater probabilities for above normal temperatures are indicated for much of this region in several models. Greater uncertainty for the upper and central Mississippi Valley and the Great Lakes regions, leads to equal chances of above-normal and below-normal temperatures in the Week 3-4 outlook. A consensus of dynamical models, including the SubX MME, predicts increase chances of above-normal temperatures along the Gulf Coast, across the Southeast region, as well as along the Atlantic Coast into the Mid-Atlantic and New England. Above-normal temperatures are more likely across southern and western mainland Alaska, the Aleutian Islands, and the Alaska Panhandle, based on dynamical model forecasts and above-normal SSTs along the west coast of Alaska. There is good agreement among dynamical models for a forecast of below-normal temperatures for northeast Alaska, where SSTs are below normal and sea ice is forming.

The East Pacific is likely to remain active, leading to potential moisture surges into the Desert Southwest. The predicted 500-hpa height anomaly pattern and the predicted location of a subtropical ridge over eastern North America leads to the potential for easterly waves to cross lower latitudes. Dynamical models forecast increased probabilities of above-median precipitation for the Desert Southwest and southern to central Rockies, related to these factors. A predicted upper-level ridge over western North America and the Gulf of Alaska, in a consensus of model forecasts, leads to a greater likelihood for below-median precipitation from the Pacific Northwest eastward to the northern Plains. Greater uncertainty in precipitation forecasts for much of the eastern CONUS leads to equal chances of above-median and below-median precipitation during Weeks 3-4. A consensus of operational and experimental dynamical model forecasts, including the ECMWF, JMA, and SubX, indicates enhanced chances for above-median precipitation along the Gulf and southern Atlantic coasts.

Sea surface temperatures remain slightly above normal surrounding Hawaii, and the consensus of dynamical model guidance, including the SubX MME, indicates enhanced probabilities for above-normal temperatures. Dynamical model precipitation forecasts indicate likely above-median rainfall throughout the Hawaiian Islands.

This  is also of interest published September 10.

GULF OF MEXICO…

An upper-level trough extends from the NE corner of the Gulf of Mexico, to the east central Gulf of Mexico, to a cyclonic circulation center that is just to the north of the Yucatan Peninsula. Upper level cyclonic wind flow covers the Gulf of Mexico east of 92W. Upper level anticyclonic wind flow covers the rest of the area. Widely scattered moderate to isolated strong rainshowers are to the east of 90W. This area of precipitation is forecast to move slowly northwestward near the Yucatan Peninsula  on Tuesday with limited development expected. Upper level winds  are forecast to become more conducive for development on Wednesday, when the system moves across the southern Gulf of Mexico. It is possible that a tropical depression may form on Thursday or Friday, while the disturbance moves across the western Gulf of Mexico. Please read the latest Tropical Weather Outlook for more details, TWOAT/ABNT20 KNHC.

A frontal trough is in the Texas coastal plains/the Texas coastal waters. Isolated moderate rainshowers are to the west of the line that runs from SE Louisiana to the coast of Mexico near 20N96W.

A surface trough in the western Caribbean will move across the Yucatan peninsula Tue, and into the Gulf of Mexico Wed. The trough will move into the western gulf Thu, and west of the area Sat. 

CARIBBEAN SEA…

Upper-level cyclonic flow associated with the upper low over the Gulf of Mexico near 25N88W covers the northwestern Caribbean Sea as well as western and central Cuba. A weak surface trough is analyzed from near 21N82.5W to near just northeast of the northeastern coast of Honduras. Scattered moderate to strong  convection increasing in coverage is observed to the north of 17N west of 79W to juts inland the coast of the Yucatan Peninsula. This activity is quickly lifting northward under moderate to strong upper-level southerly flow located to the east of the Gulf of Mexico upper-level low near 25N88W. Satellite imagery indicates that this activity is showing signs of organization, and it is forecast to move slowly northwestward near the Yucatan Peninsula on Tue with limited development expected. Upper-level winds are forecast to become more conducive for development on Wed when the system moves over the southern Gulf of Mexico.

Rainshowers that are in NW corner of the Caribbean Sea, western Cuba, the Yucatan Peninsula of Mexico, and Central America from Honduras to El Salvador and Guatemala, are associated with a surface trough, and are showing some signs of organization. This system is forecast to move slowly northwestward across the Yucatan Peninsula on Tuesday with limited development. Upper level winds are forecast to become more conducive for development later in the week. It is possible that a tropical depression may form on Thursday or Friday, while the disturbance moves across the western Gulf of Mexico. People who are in NE Mexico and the coast of Texas and Louisiana should monitor the progress of this system. It is likely that heavy rainfall and gusty winds will be present in western Cuba and the Yucatan Peninsula through Tuesday.

Some Indices of Possible Interest:  We should always remember that the forecast is driven by many factors some of which are conflicting in terms of their impacts. Please pay more attention to the graphics than my commentary which does not update on a regular basis once the article is published. The indices will continue to update.

Below is a graphical explanation of the Arctic Oscillation

AO Positive	AO Negative
There are more impacts than shown here but these are important. Basically the AO+ means the Polar Vortex is blocked from leaving its normal locations	Again there are more impacts than shown here. A0- means Low Pressure allows the Polar Vortex to wander south.

* These graphics are from National Geographic Magazine, March 2000; Sources: Doug Martinson, Wieslaw Maslowski, David Thompson, and John M. Wallace

Here is another set of graphics.

Left: Effects of the Positive Phase of the Arctic Oscillation. Right:Effects of the Negative Phase of the Arctic Oscillation. —Credit: J. Wallace, University of Washington.

NAO Positive	NAO Negative
Notice the strong Icelandic Low and strong Bermuda High but located east of where it is usually found	Notice the weak Icelandic Low and Bermuda High.
There are many variations on a theme when talking about the NAO.	Some use Lisbon or Gibraltar as the sub-arctic reference point. And there appears to be a low-frequency cycle related to the AMO to some extent. Thus the NAO is a lot more complicated than I am able to show here.  I like this explanation better than the graphics I have shown. It better captures the impact of the changing relative strength of the two control factors in the Atlantic namely the Northern and Southern semi-permanent Highs and Lows.

But it gets even more complicated. With a Negative NAO the position of the pattern more east than west or vice versa changes the impacts.

Madden Julian Oscillation (MJO)

The MJO is an area of convective activity along the Equator which circles the globe generally in 30 to 60 days. The location of the convective activity not only impacts the Equator but also the middle latitudes.

There are a lot of models and I try to read the results from all of them.  For access to a variety of models,  I refer readers here. This weekly report summarizes things.  Here is another useful source of information. 

Now we look at two models that I find very helpful. On the first graphic , the light gray shading shows the tracks which fit with 90% of the forecasts and the dark gray shading shows a smaller area that fits with 50% of the forecasts The large dot is the current location.

And here is a second model

Analogs to the Outlook.

Now let us take a detailed look at the “Analogs”.

NOAA normally provides two sets of Analogs.

A. Analogs related to the 5 day period centered on 3 days ago and the 7 day period centered on 4 days ago. “Analog” means that the weather pattern then resembles the recent weather pattern and the recent pattern is used to initialize the models to predict the 6 – 14 day Outlook.

B. There is a second set of analogs associated with the Outlook. It compares the forecast (rather than the prior period) to past weather patterns. I have not been regularly analyzing this second set of information. The first set applies to the 5 and 7 day observed pattern prior to today. The second set, relates to the correlation of the forecasted outlook 6 – 10 days out and 8 – 14 days out with similar patterns that have occurred in the past during a longer period that includes the dates covered by the 6 – 10 Day and 8 – 14 Day Outlook. The second set of analogs also has useful information as it indicates that the forecast is feasible in the sense that something like it has happened before. I am not very impressed with that approach. But in some ways both Approach A and B are somewhat similar. I conclude that if the Ocean Condition now are different then the analogs and if the state of ENSO now is different than the analogs that is a reason to have increased lack of confidence in the forecasts and vice versa.

They put the first set of analogs in the discussion with the second set available by a link so I am assuming that the first set of analogs is the most meaningful and I find it so. But NOAA prefers the first set (A) as it helps them (or at least they think it does) assess the quality of the forecast.

Here are today’s analogs in chronological order although this information is also available with the analog dates listed by the level of correlation. I find the chronological order easier for me to work with. It also helps the reader see the impact of the phases of the PDO and AMO which are shown. The first set (A) which is what I am using today applies to the 5 and 7 day observed pattern prior to today.

(t) = a month where the Ocean Cycle Index has just changed from a consistent pattern or does change the following month to a consistent pattern.

The spread among the analogs from August 22 to September 20 is 29 days which is  little tighter than last week. I have not calculated the centroid of this distribution which would be the better way to look at things but the midpoint, which is a lot easier to calculate, and fairly accurate if the dates are reasonably evenly distributed, is about September 6. These analogs are centered on 3 days and 4 days ago (Sept 6 or September 7). So the analogs could be considered to be in sync with respect to weather that we would normally be getting right now.

For more information on Analogs see discussion in the GEI Weather Page Glossary.  For sure it is a rough measure as there are so many historical patterns but not enough to be a perfect match with current conditions. I use it mainly to see how our current conditions match against somewhat similar patterns and the ocean phases that prevailed during those prior patterns. If everything lines up I have my own measure of confidence in the NOAA forecast. Similar initial conditions should lead to similar weather. I am a mathematician so that is how I think about models.

Including duplicates, there are three La Nina Analogs, seven El Nino Analogs and zero Neutral analogs. The pre-forecast analogs this week are supportive of McCabe C (Northern Tier and Mid Atlantic Drought) and unsupportive of McCabe D (Southwest Drought) Conditions. Most of the analogs are associated with PDO+. There are a lot of transitions taking place so forecasting right now is very difficult. Many of the analogs associated with El Nino conditions are Modoki’s which is consistent with the current pattern of warm and cool water in the Nino 3.4 Measurement Area.

The seminal work on the impact of the PDO and AMO on U.S. climate can be found here. Water Planners might usefully pay attention to the low-frequency cycles such as the AMO and the PDO as the media tends to focus on the current and short-term forecasts to the exclusion of what we can reasonably anticipate over multi-decadal periods of time. One of the major reasons that I write this weather and climate column is to encourage a more long-term and World view of weather.

In color	Black and White same graphics

You may have to squint but the drought probabilities are shown on the map and also indicated by the color coding with shades of red indicating higher than 25% of the years are drought years (25% or less of average precipitation for that area) and shades of blue indicating less than 25% of the years are drought years. Thus drought is defined as the condition that occurs 25% of the time and this ties in nicely with each of the four pairs of two phases of the AMO and PDO.

Historical Anomaly Analysis

When I see the same dates showing up often I find it interesting to consult this list.

A Useful Read

Some might find this analysis which you need to click to read interesting as the organization which prepares it focuses on the Pacific Ocean and looks at things from a very detailed perspective and their analysis provides a lot of information on the history and evolution of ENSO events.

Recent CONUS Weather

This is provided mainly to see the pattern in the weather that has occurred recently.

And the 30 Days ending September 1, 2018	And the 30 Days ending September 8, 2018
Biggest change is in the temperature. The cold anomaly has shrunk and moved and the western warm anomaly is far less pervasive.	You can see the improvement in the Great Plains re precipitation and we see how the Northeast is a lot warmer.
Remember, these maps are a 30 average so the most distant seven days are removed and the most recent seven days are added.

B. Beyond Alaska and CONUS Let’s Look at the World which of course also includes Alaska and CONUS

It is Useful to Understand the Semipermanent Pattern that Control our Weather and Consider how These Change from Winter to Summer. These two graphics (click on each one to enlarge) are from a much larger set available from the Weather Channel.  They highlight the position of the Bermuda High which they are calling the Azores High in the January graphic and is often called NASH and it has a very big impact on CONUS Southeast weather and also the Southwest. You also see the north/south migration of the Pacific High which also has many names and which is extremely important for CONUS weather and it also shows the change of location of the ITCZ which I think is key to understanding the Indian Monsoon. A lot of things become much clearer when you understand these semi-permanent features some of which have cycles within the year, longer period cycles and may be impacted by Global Warming. We are now moving into Mid-September and we should be returning from the set of positions shown below for July back slowly to the Winter Pattern. For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant.

World Forecasts

A. Today (University of Maine)

B  Short-term set for day six but can be adjusted (BOM – Australia)

C. 8 – 14 Day (NOAA/Canada/Mexico Experimental NAEFS))

A. Forecast for Today (you can click on the maps to enlarge them)

And now precipitation

I have not changed the source but it seems that the links I had before (the images were smaller and in a table) were not updating. We will see if this works better.

Additional Maps showing different weather variables can be found here.

B. Forecast for Day 6 (Currently Set for Day 6 but the reader can change that)

World Weather Forecast produced by the Australian Bureau of Meteorology. Unfortunately I do not know how to extract the control panel and embed it into my report so that you could use the tool within my report. But if you visit it Click Here and you will be able to use the tool to view temperature or many other things for THE WORLD. It can forecast out for a week. Pretty cool. Return to this report by using the “Back Arrow” usually found top left corner of your screen to the left of the URL Box. It may require hitting it a few times depending on how deep you are into the BOM tool. Below are the current worldwide precipitation and temperature forecasts for six days out. They will auto-update and be current for Day 6 whenever you view them. If you want the forecast for a different day Click Here

Please remember this graphic updates every six hours so the diurnal pattern can confuse the reader.

Now Precipitation

C. And now we have experimental 8 – 14 Day World forecasts from the NAEFS Model.

First Temperature

Then Precipitation

Looking Out a Few Months

Here is the precipitation forecast from Queensland Australia:

It is kind of amazing that you can make a worldwide forecast based on just one parameter the SOI and changes in the SOI. This graphic has been updated and now is in line with the actual SOI for June and July. Of interest is generally dry CONUS and belt of wet in the mid Asian Continent and belt of dry for Equatorial Africa and the Middle East. Eastern Asia and Australia are wet.

Sea Surface Temperature (SST) Departures from Normal for this Time of the Year i.e. Anomalies

My focus here is sea surface temperature anomalies as they are one of the two largest factors determining weather around the World. If we want to have a good feel for future weather we need to look at the oceans as our weather mostly comes from oceans and we need to look at

• Surface temperature anomalies (weather develops from the ocean surface and
• The changes in the temperature anomalies since that may provide clues as to how the surface anomalies will change based on the current trend of changes. This is not that easy to do since the oceans are deep, there are many currents, winds have an impact etc. Two ways that are available to use are to look at the change in the situation today compared to the average over a period of time and NOAA also produces a graphic of monthly changes. I use both. The first set of graphics is simply looking at the average compared to today and that is below.

Three Month Average Anomaly	Current Anomaly
By this point La Nina is gone	Traces of El Nino but the Indo-Pacific Warm Pool is cool. I am not convinced an El Nino will materialize.

And when we look in more detail at the current Sea Surface anomalies below, we see a lot of them not just along the Equator related to ENSO.

First the categorization of the current daily SST anomalies.
Mediterranean, Black Sea and Caspian Sea	Western Pacific	West of North America	North and East of North America	North Atlantic
The Black Sea is warm. The Mediterranean is slightly warm The Gulf of Aden and the Arabian Sea are slightly cool	Neutral east of southern Asia Very warm around Kamchatka and east of Japan	Warm Chukchi Sea Slightly warm offshore of British Columbia Warm off Baja	Hudson Bay cool Great Lakes Warm Cool south of Greenland Warm offshore of Nova Scotia down to Cape Hatteras extending far out to sea	Scandinavia warm
Equator	Still looks like Neutral
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Slightly cool west coast of Africa north of the  Equator. Cool Gulf of Guinea Warm south of Africa	Cool	Cool to the northwest Cool to the south and  southwest	Generally cool from 30S north La Nina lives	Slightly warm off 30S to 50S

Then we look at the change in the anomalies. The SST anomaly is sort of like the first derivative and the change in the anomaly is somewhat like a second derivative. It tells us if the anomaly is becoming more or less intense.

Here it gets a little tricky as for this graphic red does not mean a warm anomaly but a warming of the anomaly which could mean more warm or less cool and blue does not mean cool but more cool or less warm.
Mediterranean, Black Sea and Caspian Sea	Western North Pacific	West of North America	East of North America	North Atlantic
Western Mediterranean cooling Black sea is warming Caspian Sea is cooling.	Cooling west of Japan. Slight cooling in Bering Sea	Warming west of Baja and Mexico .	Cooling Hudson Bay Warming off Nova Scotia and far south of Greenland Slight cooling Davis strait	Significant cooling around British Isles and further north.
Equator	Eastern Pacific showing a bit more warming
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Warming west of North Africa in narrow band extending to north of South America. Cooling west of Africa south of Equator Warming south of Africa	Fairly Neutral	Warming to the  southwest, cooling to the east to but not beyond New Zealand	Fairly Neutral except warming offshore at 40S	Cooling north of South America at 50W Warming offshore at 20S to 30S extending to the cooling west of Africa.

This may be a good time to show the recent values to the indices most commonly used to describe the overall spacial pattern of temperatures in the (Northern Hemisphere) Pacific and the (Northern Hemisphere) Atlantic and the Dipole Pattern in the Indian Ocean. Notice the change in the PDO in July of 2017 and the stability of the AMO index.

Switching gears, below is an analysis of projected tropical hazards and benefits over an approximately two-week period.

 * Moderate Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend.** High Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend.

Tropical Activity Possibly Impacting CONUS.

When there is activity and I have not provided the specific links to the storm of “immediate” interest, one can obtain that information at this link. At this point in time, no (new) tropical events are expected to appear in this graphic during the next 48 hours. If that changes, we will provide an update.

Now let us look at the Western Pacific in Motion.

The above graphic which I believe covers the area from the Dateline west to 100E and from the Equator north to 45N normally shows the movement of tropical storms towards Asia in the lower latitudes (Trade Winds) and the return of storms towards CONUS in the mid-latitudes (Prevailing Westerlies). This is recent data not a forecast. But, it ties in with the Week 1 forecast in the graphic just above this graphic. Information on Western Pacific storms can be found clicking U.S. Navy Joint Typhoon Warning Center This (click here to read) is an unofficial private source but one that is easy to read but not working right now. And then there is the Central Pacific Hurricane Warning Center.

In the above graphic, it is difficult to reference the storms to geography. If you are patient and look closely you can see bodies of land under the storms. Mostly I am interested in

1. How much of the tropical activity gets caught up in the westerlies and returns to CONUS and
2. How much of the Asian storms return along the northern route to Alaska and British Columbia.

C. Progress of ENSO

This section is organized into four parts.

1. Current and Recent Sea Surface Temperatures (SST)

2. Current and Recent Equatorial Pacific Subsurface Temperatures

3. History of the Nino 3.4 Readings and forecasts from other Meteorological Agencies.

4. The Surface Air Pressure Pattern that confirms the state of ENSO.

1. Current and Recent Sea Surface Temperatures (SST)

A major driver of weather is Surface Ocean Temperatures. Evaporation only occurs from the Surface of Water. So we are very interested in the temperatures of water especially when these temperatures deviate from seasonal norms thus creating an anomaly. The geographical distribution of the anomalies is very important. To a substantial extent, the temperature anomalies along the Equator have disproportionate impact on weather so we study them intensely and that is what the ENSO (El Nino – Southern Oscillation) cycle is all about. Subsurface water can be thought of as the future surface temperatures. They may have only indirect impacts on current weather but they have major impacts on future weather by changing the temperature of the water surface. Winds and Convection (evaporation forming clouds) is weather and is a result of the Phases of ENSO and also a feedback loop that perpetuates the current Phase of ENSO or changes it. That is why we monitor winds and convection along or near the Equator especially the Equator in the Eastern Pacific.

It is the ocean surface that interacts with the atmosphere and causes convection and also the warming and cooling of the atmosphere. So we are interested in the actual ocean surface temperatures and the departure from seasonal normal temperatures which is called “departures” or “anomalies”. Since warm water facilitates evaporation which results in cloud convection, the pattern of SST anomalies suggests how the weather pattern east of the anomalies will be different than normal.

A major advantage of the Hovmoeller method of displaying information is that it shows the history so I do not need to show a sequence of snapshots of the conditions at different points in time. This Hovmoeller provides a good way to visually see the evolution of this ENSO event. I have decided to use the prettied-up version that comes out on Mondays rather that the version that auto-updates daily because the SST Departures on the Equator do not change rapidly and the prettied-up version is so much easier to read. The bottom of the Hovmoeller shows the current readings. Remember the +5, -5 degree strip around the Equator that is being reported in this graphic. So it is the surface but not just the Equator.

This next graphic is more focused on the Equator and looks down to 300 meters rather than just being the surface.

2. Current and Recent Equatorial Pacific Subsurface Temperatures Let us look in more detail at the Equatorial Water Temperatures.

 This graphic provides both a summary perspective and a history (small images on the right).

.

Anomalies are strange. You can not really tell for sure if the blue area is colder or warmer than the water above or below. All you know is that it is cooler than usual for this time of the year. A later graphic will provide more information. Aside from buoyancy the currents tend to bring water from that depth up to the surface mostly farther east. These currents are very complicated and made even more so by the uneven nature of the ocean floor. So the exact pattern of where this warm water will erupt is beyond my level of understanding. But it will erupt to the surface in multiple different places.

Now for a more detailed look. Below is the pair of graphics that I regularly provide. The date shown is the midpoint of a five-day period with that date as the center of the five-day period. The bottom graphic shows the absolute values, the upper graphic shows anomalies compared to what one might expect at this time of the year in the various areas both 130E to 90W Longitude and from the surface down to 450 meters. At different times I have discussed the difference between the actual values and the deviation of the actual values from what is defined as current climatology (which adjusts every ten years except along the Equator where it is adjusted every five years) and how both measures are useful for other purposes.

We now have warm water with a maximum anomaly of +1C from 140W but  only to 120W with additional warm water extending west to Indonesia. But overall, it again is more Neutral than last week.

The 28C Isotherm is now at 170W, the 27C Isotherm is at 150W, the 25C Isotherm is now at 130W. The 20C Isotherm has now reached the surface at 100W as the Kelvin Wave has pretty much played out near the coast of Ecuador. But east of 100W, the water is not quite as cold.

Tracking the change.

The next graphic basically averages out the anomalies by longitude.

The discussion in this slide says it better than I could. One might compare the current reading to Oct/Nov 2017. The anomaly had returned to zero then reversed for a month and then returned to zero and now has gone positive. It now seems to be declining a bit.

Side by side comparison can be useful

Comparison Week Probably Third Week of December 2017	Current Week

3. History of the Nino 3.4 Readings and forecasts from other Meteorological Agencies.

TAO/TRITON GRAPHIC (a good way of viewing data related to the part of the Equator and the waters close to the Equator in the Eastern Pacific where we monitor to determining the current phase of ENSO. It is probably not necessary in order to follow the discussion below, but here is a link to TAO/TRITON terminology.

And here is the current version of the TAO/TRITON Graphic. The top part shows the actual temperatures, the bottom part shows the anomalies i.e. the deviation from normal.

Location Bar for Nino 3.4 Area Above and Below

My Calculation of the Nino 3.4 Index

I calculate the current value of the Nino 3.4 Index each Monday using a method that I have devised. To refine my calculation, I have divided the 170W to 120W Nino 3.4 measuring area into five subregions (which I have designated from west to east as A through E) with a location bar shown under the TAO/TRITON Graphic). I use a rough estimation approach to integrate what I see below and record that in the table I have constructed. Then I take the average of the anomalies I estimated for each of the five subregions.

So as of Monday September 10, in the afternoon working from the September 9 TAO/TRITON report [Although the TAO/TRITON Graphic appears to update once a day, in reality it updates more frequently.], this is what I calculated.

Calculation of Nino 3.4 from TAO/TRITON Graphic

My estimate of the daily Nino 3.4 SST anomaly tonight is +0.4 which is an ENSO Neutral value. NOAA has reported the weekly Nino 3.4 to be +0.3 which is an ENSO Neutral value. Nino 4 is reported to be a bit warmer than last week at +0.5. Nino 3 is reported to be warner at +0.1. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported slightly cooler at -0.4 It was close to -3.0 at one time so this index has been declining as an anomaly (rising) quite a bit and also fluctuating quite a bit which is not surprising as it is the area most impacted by the Upwelling off the coast. So it is an indication of the interaction between surface water and rising cool water. Thus it is subject to larger changes. I am only showing the currently issued version of the NINO SST Index Table as the prior values are shown in the small graphics on the right with this graphic. The same data in graphic form but going back a couple of more years can be found here.  The full table of values can be found here.

This graphic brings the Nino 3.4 up to date and is easy to read. It may be more reliable than the NOAA readings. And Memorial Day is not a Holiday in Australia.

Here is another way of looking at the TAO/TRITON Graphic. It is a fast way to assess the strength of an ENSO Event and provides a way to track it.  

The below table only looks at the Equator and shows the extent of anomalies along the Equator. The ONI Measurement Area is the 50 degrees of Longitude between 170W and 120W and extends 5 degrees of Latitude North and South of the Equator so the above table is just a guide and a way of tracking the changes. The top rows show El Nino anomalies. The two rows just below that break point contribute to ENSO Neutral.

Forecasting the Evolution of ENSO

The CFS.v2 is not the only forecast tool used by NOAA. The CPC/IRI Analysis which is produced out of The International Research Institute (IRI) for Climate and Society at Columbia University is also very important to NOAA.

Here is the most recent update. We expect a new update on August 9, 2018

The discussion released with the forecast can be found here.

Sometimes it is useful to compare the new forecast to the old.

This graphic shows a collection of models used by various meteorological agencies to forecast the NINO 3.4 Index

Forecasts from Other Meteorological Agencies.

Here is the newly issued JAMSTEC Model Forecast.  It suggests a less strong El Nino than their forecast last month.  One can always find the latest JAMSTEC maps by clicking this link. You will find additional maps that I do not general cover in my monthly Update Report.  Remember if you leave this page to visit links provided in this article, you can return by hitting your “Back Arrow”, usually top left corner of your screen just to the left of the URL box.

We now have the short discussion that goes with the above ENSO Forecast.

Aug. 20, 2018

Prediction from 1st Aug., 2018

ENSO forecast:

The SINTEX-F predicts that a moderate-to-strong El Niño event may start in early fall and reach its peak in winter. This El Niño is more or less of Modoki-type and we need to be careful of its impact that may be different from that of the canonical El Niño.

Indian Ocean forecast:

As predicted earlier, the positive Indian Ocean Dipole (IOD) has actually emerged in July. The model continues predicting the positive IOD for the boreal fall. In accord to the positive IOD evolution, sea level anomalies are expected to be negative (positive) in the eastern (western) tropical Indian Ocean. We may observe co-occurrence of a positive Indian Ocean Dipole and an El Niño/El Niño Modoki-like state in the latter half of 2018; this is as we observed in 1994 (with El Niño Modoki) or 1997 and 2015 (with El Niño).

Regional forecast:

On a seasonal scale, most part of the globe will experience a warmer-than-normal condition in fall, while some parts of southern Africa and Tibet will experience a cooler-than-normal condition. In winter, most part of the globe will be in a warmer-than-normal condition, while southern Alaska, western U.S.A., northern Brazil, Botswana, northern India, Iran, Afghanistan, northeastern Russia, and Tibet will experience a relatively cold condition.

As regards to the seasonally averaged rainfall in boreal fall, a wetter-than-normal condition is predicted for most parts of Alaska, western/eastern Canada, central/eastern U.S.A., East Africa, West Africa, and northern Europe. In contrast, northwestern/southeastern U.S.A., eastern Brazil, eastern Europe, South Korea, India, Southeast Asia, the Philippines, Indonesia and Australia will experience a drier-than-normal condition. In particular, we notice that Indonesia and Australia may be extremely drier than normal, owing to the expected co-occurrence of a positive Indian Ocean Dipole and an El Niño/El Niño Modoki-like state.

In winter, we expect a drier-than-normal condition in northern South American Continent, Australia, Mozambique, South Africa, southern Angola, Zambia, southeastern Europe facing the Mediterranean Sea, northern Europe, southern India, Southeast Asia, the Philippines, Indonesia and Australia. On the other hand, most parts of U.S.A, northeastern/south Brazil, northern South Africa, Botswana, western Europe, southeastern China will be wetter-than-normal.

Most part of Japan will experience warmer-than-normal condition in fall and winter as a seasonal average.

Here is the Nino 3.4 report from the Australian BOM (it updates every two weeks)

And the ENSO Outlook Discussion Issued on September 11, 2018

El Niño still possible in 2018

The El Niño–Southern Oscillation (ENSO) remains neutral. However model outlooks continue to indicate El Niño is possible from late spring 2018. When assessed with current observations, the Bureau’s ENSO Outlook stands at El Niño WATCH, meaning there is approximately a 50% chance of El Niño forming in the coming months—double the normal chance.

There were only small changes to most indicators of ENSO in the past fortnight. The central and eastern tropical Pacific Ocean are warmer than average, with greatest warmth in the central to western Pacific (NINO4; +0.6 °C), while water below the surface remains somewhat warmer than average. Atmospheric indicators generally remain neutral, although trade winds are slightly weaker over parts of the western Pacific. A weakening of the trade winds is one of the most important precursors at this point for any possible El Niño, and will be watched closely.

Seven of the eight surveyed models suggest SSTs are likely to reach or exceed El Niño thresholds by the end of spring, with the majority suggesting values will remain at or above the threshold into early 2019. El Niño during spring typically results in below-average rainfall in eastern and northern Australia. In summer, this drying influence retracts to tropical regions of Australia, although the possibility of high temperatures elsewhere remains high.

Regardless of El Niño or positive IOD developing, the climate outlook for spring is for a continuation of drier and warmer than average conditions across eastern and southwest Australia.

Indian Ocean IOD (It updates every two weeks)

Indian Ocean Dipole Outlook  Discussion Issued September 11, 2018

Indian Ocean Dipole outlooks

The Indian Ocean Dipole (IOD) is currently neutral. The weekly index value to 9 September was +0.28 °C.  However, two of six international climate models suggest a positive IOD event may develop before the end of spring. A positive IOD during spring typically reduces rainfall in central and southern Australia, and can exacerbate any El Niño-driven rainfall deficiencies.

It is useful to understand where and how the IOD is measured.

IOD Positive is the West Area being warmer than the East Area (with of course many adjustments/normalizations). IOD Negative is the East Area being warmer than the West Area. Notice that the Latitudinal extent of the western box is greater than that of the eastern box. This type of index is based on observing how these patterns impact weather and represent the best efforts of meteorological agencies to figure these things out. Global Warming may change the formulas probably slightly over time but it is costly and difficult to redo this sort of work because of long weather cycles.

4. The Surface Air Pressure Pattern that confirms the state of ENSO.

And Now the Air Pressure to Confirm that the Atmosphere is Reacting to the Sea Surface Temperature Pattern. The most Common way to do that is to use an Index called the SOI.

This index provides an easy way to assess the location of and the relative strength of the Convection (Low Pressure) and the Subsidence (High Pressure) near the Equator. Experience shows that the extent to which the Atmospheric Air Pressure at Tahiti exceeds the Atmospheric Pressure at Darwin Australia when normalized is substantially correlated with the Precipitation Pattern of the entire World. At this point there seems to be no need to show the daily preliminary values of the SOI but we can work with the 30 day and 90 day values.

Current SOI Readings

SOI = 10 X [ Pdiff – Pdiffav ]/ SD(Pdiff) where Pdiff = (average Tahiti MSLP for the month) – (average Darwin MSLP for the month), Pdiffav = long term average of Pdiff for the month in question, and SD(Pdiff) = long term standard deviation of Pdiff for the month in question. So really it is comparing the extent to which Tahiti is more cloudy than Darwin, Australia. During El Nino we expect Darwin Australia to have lower air pressure and more convection than Tahiti (Negative SOI especially lower than -7 correlates with El Nino Conditions). During La Nina we expect the Warm Pool to be further east resulting in Positive SOI values greater than +7).

To some extent it is the change in the SOI that is of most importance. The MJO or Madden Julian Oscillation is an important factor in regulating the SOI and Ocean Equatorial Kelvin Waves and other tropical weather characteristics. More information on the MJO can be found here. Here is another good resource.

And now let us look at the atmosphere.

This graphic shows the Low-Level Wind Anomalies near the Equator. The 850 hPa level is above the surface but close to the surface.	And now the Outgoing Long-wave Radiation (OLR) Anomalies which tell us where convection has been taking place. The bottom of a Hovmoeller graphic shows the most recent readings.
Reds and browns would be suppressed easterlies or enhanced westerlies and are typical of El Nino. It looks pretty neutral.	We see the change in the pattern of suppressed OLR along the Dateline as the La Nina declines. But we now see suppressed OLR further west.

D. Putting it all Together.

At this time, La Nina Conditions along the Equator have come to an end and we are solidly into ENSO Neutral and possibly entering El Nino Conditions. But the drivers of a transition to El Nino are not solidly in place.

Forecasting Beyond Five Years.

So in terms of long-term forecasting, none of this is very difficult to figure out actually if you are looking at say a five-year or longer forecast.

The research on Ocean Cycles is fairly conclusive and widely available to those who seek it out. I have provided a lot of information on this in prior weeks and all of that information is preserved in Part II of my report in the Section on Low Frequency Cycles 3. Low Frequency Cycles such as PDO, AMO, IOBD, EATS. It includes decade by decade predictions through 2050. Predicting a particular year is far harder.

The odds of a climate shift for the Pacific taking place have significantly increased. It may be in progress. The AMO is pretty much neutral at this point so it may need to become a bit more negative for the “McCabe A” pattern to become established. Our assessment is that the standard time for Climate Shifts in the Pacific is likely to prevail and it most likely will be a gradual process with a speed up in less than five years but more than two years. The next El Nino may be the trigger. And of course the next El Nino is project to occur this winter.

E. Relevant Recent Articles and Reports

Weather in the News  

Nothing to Report

Weather Research in the News

Nothing to Report

Global Warming in the News

Nothing to Report

F. Table of Contents for Page II of this Report Which Provides a lot of Background Information on Weather and Climate Science

The links below may take you directly to the set of information that you have selected but in some Internet Browsers it may first take you to the top of Page II where there is a TABLE OF CONTENTS and take a few extra seconds to get you to the specific section selected. If you do not feel like waiting, you can click a second time within the TABLE OF CONTENTS to get to the specific part of the webpage that interests you.

1. Very High Frequency (short-term) Cycles PNA, AO,NAO (but the AO and NAO may also have a low frequency component.)

2. Medium Frequency Cycles such as ENSO and IOD

3. Low Frequency Cycles such as PDO, AMO, IOBD, EATS.

4. Computer Models and Methodologies

5. Reserved for a Future Topic (Possibly Predictable Economic Impacts)

G. Table of Contents of Contents for Page III of this Report – Global Warming Which Some Call Climate Change.

The links below may take you directly to the set of information that you have selected but in some Internet Browsers it may first take you to the top of Page III where there is a TABLE OF CONTENTS and take a few extra seconds to get you to the specific section selected. If you do not feel like waiting, you can click a second time within the TABLE OF CONTENTS to get to the specific part of the webpage that interests you.

1. Introduction

2. Climate Impacts of Global Warming

3. Economic Impacts of Global Warming

4. Reports from Around the World on Impacts of Global Warming

H. Useful Background Information

The current conditions are measured by determining the deviation of actual sea surface temperatures from seasonal norms (adjusted for Global Warming) in certain parts of the Equatorial Pacific. The below diagram shows those areas where measurements are taken.

NOAA focuses on a combined area which is all of Region Nino 3 and part of Region Nino 4 and it is called Nino 3.4. They focus on that area as they believe it provides the best correlation with future weather for the U.S. primarily the Continental U.S. not including Alaska which is abbreviated as CONUS. The historical approach of measurement of the impact of the sea surface temperature pattern on the atmosphere is called the Southern Oscillation Index (SOI) which is the difference between the atmospheric pressure at Tahiti as compared to Darwin Australia. It was convenient to do this as weather stations already existed at those two locations and it is easier to have weather stations on land than at sea. It has proven to be quite a good measure. The best information on the SOI is produced by Queensland Australia and that information can be found here. SOI is based on Atmospheric pressure as a surrogate for Convection and Subsidence. Another approach made feasible by the use of satellites is to measure precipitation over the areas of interest and this is called the El Nino – Southern Oscillation (ENSO) Precipitation Index (ESPI). We covered that in a weekly Weather and Climate Report which can be found here. Our conclusion was that ESPI did not differentiate well between La Nina and Neutral. And there is now a newer measure not regularly used called the Multivariate ENSO Index (MEI). More information on MEI can be found here. The jury is still out on MEI and it is not widely used.

The below diagram shows the usual location of the Indo-Pacific Warm Pool. When the warm water shifts to the east we have an El Nino; to the west a La Nina.

Click for Source

Interaction between the MJO and ENSO

This Table is a first attempt at trying to relate the MJO to ENSO

History of ENSO Events as measured by the ONI

The new SON reading of +0.1 is clearly an ENSO Neutral reading. The full history of the ONI readings can be found here. The MEI index readings can be found here.

Four Quadrant Jet Streak Model Read more here This is very useful for guessing at weather as a trough passes through. It would apply to the states that are at the apex of the trough.

If the centripetal accelerations owing to flow curvature are small, then we can use the “straight” jet streak model. The schematic figure directly below shows a straight jet streak at the base of a trough in the height field. The core of maximum winds defining the jet streak is divided into four quadrants composed of the upstream (entrance) and downstream (exit) regions and the left and right quadrants, which are defined facing downwind.

Isotachs are shaded in blue for a westerly jet streak (single large arrow). Thick red lines denote geopotential height contours. Thick black vectors represent cross-stream (transverse) ageostrophic winds with magnitudes given by arrow length. Vertical cross sections transverse to the flow in the entrance and exit regions of the jet (J) are shown in the bottom panels along A-A’ and B-B’, respectively. Convergence and divergence at the jet level are denoted by “CON” and “DIV”. “COLD” and “WARM” refer to the air masses defined by the green isentropes.

[Editor’s Note: There are many undefined words in the above so here are some brief definitions. Isotachs are lines of equal wind speed. Convergence is when there is an inflow of air which tends to force the air higher with cooling and cloud formation. Divergence is when there is an outflow of air which tends to result in air sinking which causes drying and warming, Confluence is when two streams of air come together. Diffluence is when part of a stream of air splits off.]

Here is a time sequence animation. You may have to click on them to get the animation going.

When we discuss the jet stream and for other reasons, we often discuss different layers of the atmosphere. These are expressed in terms of the atmospheric pressure above that layer. It is kind of counter-intuitive to me. The below table may help the reader translate air pressure to the usual altitude and temperature one might expect at that level of air pressure. It is just an approximation but useful.

Re the above, H8 is a frequently used abbreviation for the height of the 850 millibar level (which is intended to represent the atmosphere above the Boundary Layer most impacted by surface conditions), H7 is the 700 mb level, H5 is the 500 mb level, H3 is the 300 mb level. So if you see those abbreviations in a weather forecast you will know what they are talking about.

MJO (Madden Julian Oscillation)

The MJO is an area of convective activity along the Equator which circles the globe generally in 30 to 60 days. The location of the convective activity not only impacts the Equator but also the middle latitudes. Here is a good description of the MJO.

This is the source of the analysis of the impact of the MJO on CONUS. “A composite study of the MJO influence on the surface air temperature and precipitation over the Continental United States Shuntai Zhou • Michelle L’Heureux • Scott Weaver • Arun Kumar”

The below shows the various phases of the MJO. Where the above average convection (green) is found is described by one of 8 phases shown below. The dry part of the pattern is shown in brown and is called the Inactive or dry part of the MJO.

The below is the summary analysis for precipitation in the July to September Season. The full data set for all seasons can be found here for Temperature and here for Precipitation. My analysis of that data was that there is not much difference between the level of significance of the temperature and precipitation in the JAS three-month period.