September 18, 2017 Weather and Climate Report – Fall and La Nina Arrive

Written by Sig Silber

As of September 14, 2017, The ENSO Alert System Status has changed to : La Nina Watch, For all practical purposes, we are entering a weak La Nina. Similarly, the weather pattern is changing to a Fall Pattern for the Northern Hemisphere. That is happening while the Tropical Cyclone Season remains in full swing. Transitions can be difficult.

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We have been publishing daily and more frequent updates on tropical storms. To keep the commentary up to date has meant republishing the articles daily which changes the URL. So to find them if you have an interest, the best way is to go to the Directory and click on the top link.

We will do a full analysis on the long-term forecasts of NOAA and JAMSTEC on September 23 but here is a tease.

A. Focus on Alaska and CONUS (all U.S.. except Hawaii)

First Let us focus on the Current (Right Now to 5 Days Out) Weather Situation.

Water Vapor.

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

Below is the same graphic as above but without the animation to show the current situation with respect to water vapor imagery for North America. It also covers more of CONUS.

Looking at the current activity of the Jet Stream.

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.

This graphic provides a good indication of where the moisture is. It is a bit different than just moisture imagery as it is quantitative.

You can convert the above graphic in to a flexible forecasting tool by clicking here.  One can obtain views of different geographical areas by clicking here. 

Day One CONUS Forecast

Day Two CONUS Forecast

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.

Tropical Activity

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. Information on Jose and Maria can be found by going to the Directory and clicking on the top link that is a hurricane update. .

Below is a graphic which highlights the forecasted surface Highs and the Lows re air pressure on Day 6. The Day 3 forecast can be found here. I used to present the Day 3 with a link to Day 6 but showing Day 6 may be more useful.

Now looking at the Day 5 Jet Stream Forecast.

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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.

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.

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.

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.

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

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. Because “Thickness Lines” are shown by those green lines on this graphic, it is a good place to define “Thickness” and its uses. The 540 Level general signifies equal chances for snow at sea level locations.Thickness of 600 or more suggests very intensely heat and fire danger.

Four- Week Outlook

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

I am starting with a summary of small images of the three short-term maps. This summary provides a quick look. I could have made it so you could click and enlarge the small images but for the moment I prefer that you go past the summary for the larger versions because if I set up such links, the chances increase that you will not back out of the link properly and get lost. For most people the summary with the small images will be sufficient. Following the graphic with the three small images, you can find the larger maps and a discussion and for reference purposes I then also provide the forecast map for the current or soon to be current full month and the three-month forecast map. These are issued and updated less frequently than the first three maps shown.

Small Images of Temperature Maps

6 to 10 Days	8 to 14 Days	Weeks 3 and 4
The above shows the progression of forecasts from six days out through four weeks out. Larger maps with discussion appear below. But this set of three maps paints a pretty good picture of what the forecast is.

Now the larger maps followed by a discussion that describes what is happening and any inconsistences that I see.

6 – 10 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 18, 2017 was 3 out of 5)

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 18, 2017 was 2 out of 5).

Looking further out.

Reference Forecasts Full Month and Three Months.

Below is the Temperature Outlook for the month shown in the Legend. This map is first issued on the Third Thursday of the Month for the following month and then updated on the last day of the month. The 6 – 10 day and 8 – 14 Day update daily and the Week 3/4 Map Updates every Friday so usually these are more up-to-date.  Note that the three maps shown at the beginning of this discussion on temperature may cover a slightly different time period since they update as the month progresses and the map below covers a particular month shown in the Legend. It is useful if one wants to understand how that month is forecast to play out.

Here is the Temperature Outlook issued on the date and for the three-month period shown in the Map Legend. Again this is provided for reference only. It is the same map that is included in our Saturday night report that follows the NOAA third Thursday of the month Seasonal Outlook Update. It provides a longer time frame than the above maps. It uses a totally different methodology as it is not possible to use the dynamical models to project out three months. The dynamical models work by figuring out how the current conditions will evolve over a fairly short period of time. To look out three months or longer the approach is more statistical using the forecasted ENSO Phase and Climate Trends.

Now – Precipitation

I am starting with a summary of small images of the three short-term maps. This summary provides a quick look. I could have made it so you could click and enlarge the small images but for the moment I prefer that you go past the summary for the larger versions because if I set up such links, the chances increase that you will not back out of the link properly and get lost. For most people, the summary with the small images will be sufficient. Following the graphic with the three small images, you can find the larger maps and a discussion and for reference purposes I then also provide the forecast map for the current or soon to be current full month and the three-month forecast map. These are issued and updated less frequently than the first three maps shown.

Small Images of Precipitation Maps

6 to 10 Day	8 to 14 Day	Weeks 3 and 4
The above shows the progression of forecasts from six days out through four weeks out. Larger maps with discussion appear below. But this set of three maps paints a pretty good picture of what the forecast is.

Now the larger maps followed by a discussion that describes what is happening and any inconsistencies that I see.

6 – 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 18 was 4 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 18, 2017 was 2 out of 5)

Looking further out.

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Reference Forecasts Full Month and Three Months.

Below is the Precipitation Outlook for the month shown in the Legend. This map is first issued on the Third Thursday of the Month for the following month and then updated on the last day of the month. The 6 – 10 day and 8 – 14 Day update daily and the Week 3/4 Map Updates every Friday so usually these are more up to date. Note that the three maps shown at the beginning of this discussion about precipitation may cover a slightly different time period since they update as the month progresses and the map below covers a particular month shown in the Legend. It is useful if one wants to understand how that month is forecast to play out.

Below is the Precipitation Outlook issued on the date and for the three-month period shown in the Map Legend. Again, this is provided for reference only. It is the same map that is included in our Saturday night report that follows the NOAA third Thursday of the month Seasonal Outlook Update. It provides a longer time frame than the above maps. It uses a totally different methodology as it is not possible to use the dynamical models to project out three months. The dynamical models work by figuring out how the current conditions will evolve over a fairly short period of time. To look out three months or longer, the approach is more statistical using the forecasted ENSO Phase and Climate Trends.

Here is the NOAA discussion released today September 18, 2017

6-10 DAY OUTLOOK FOR SEP 24 – 28 2017

TODAY’S MODELS ARE IN FAIRLY GOOD AGREEMENT ON AN AMPLIFIED FLOW PATTERN OVER MUCH OF THE FORECAST DOMAIN. HOWEVER, CONFIDENCE IS LOWER ALONG THE EAST COAST OF THE CONUS DUE TO UNCERTAINTIES SURROUNDING THE EVOLUTION OF HURRICANES JOSE AND MARIA. A TROUGH IS FORECAST OVER MAINLAND ALASKA AND A DEEP, POSITIVELY TILTED TROUGH IS PREDICTED OVER OVER MUCH OF THE WESTERN CONUS. RIDGING AND ABOVE NORMAL HEIGHTS ARE INDICATED DOWNSTREAM OVER THE GREAT LAKES AND NORTHEAST. ENSEMBLE SPREAD IS HIGH NEAR THE EAST COAST OF THE CONUS IN ASSOCIATION WITH THE PREDICTED PATHS OF HURRICANES JOSE AND MARIA. MOST ECMWF AND GFS ENSEMBLE SOLUTIONS CURVE JOSE OUT TO SEA PRIOR TO THE PERIOD BUT A SUBSET OF ENSEMBLE MEMBERS THEN RE-CURVE IT CLOSER TO THE MID ATLANTIC COAST NEAR THE BEGINNING OF THE PERIOD AS A WEAKER SYSTEM. MEANWHILE, MOST ENSEMBLE MEMBERS FROM THE ECMWF AND THE GFS CURVE MARIA NORTHWARD CLOSE TO THE EAST COAST DURING THE OUTLOOK PERIOD. INTERESTS ALONG THE EAST COAST SHOULD CLOSELY MONITOR THE LATEST UPDATES FROM THE NHC FOR TRACK AND INTENSITY GUIDANCE AND POTENTIAL IMPACTS FROM BOTH MARIA AND JOSE. TODAY’S MANUAL 500-HPA HEIGHT BLEND IS WEIGHTED MOST HEAVILY TOWARD THE 0Z ECMWF ENSEMBLE MEAN SOLUTION BASED PRIMARILY ON CONSIDERATIONS OF RECENT SKILL.

THE TROUGH OVER THE WESTERN CONUS TILTS THE ODDS TO BELOW NORMAL TEMPERATURES FOR MUCH OF THE INTERIOR WEST, EXTENDING TO MUCH OF THE NORTHERN AND CENTRAL PLAINS AND PARTS OF THE SOUTHERN HIGH PLAINS. HOWEVER, ABOVE NORMAL TEMPERATURES ARE SLIGHTLY FAVORED ALONG PASTS OF THE CALIFORNIA COAST DUE, IN PART, TO ABOVE NORMAL SSTS. RIDGING AND NEAR TO ABOVE NORMAL HEIGHTS AHEAD OF THE TROUGH ENHANCE PROBABILITIES OF ABOVE NORMAL TEMPERATURES FOR THE EASTERN CONUS AND MUCH OF THE SOUTHERN PLAINS. ABOVE NORMAL HEIGHTS FAVOR ABOVE NORMAL TEMPERATURES FOR MUCH OF EASTERN AND CENTRAL MAINLAND ALASKA AND THE PANHANDLE. ENHANCED PROBABILITIES FOR BELOW NORMAL TEMPERATURES ARE INDICATED FOR PARTS OF THE ALASKA PENINSULA AND EASTERN ALEUTIANS BEHIND A PREDICTED TROUGH.

THERE ARE ENHANCED PROBABILITIES FOR ABOVE NORMAL PRECIPITATION OVER MUCH OF THE CENTRAL CONUS EAST OF THE TROUGH OVER THE WESTERN CONUS. BELOW NORMAL PRECIPITATION IS FAVORED WEST OF THE TROUGH AXIS FOR THE NORTHWESTERN CONUS. THE TROUGH OVER ALASKA LEADS TO INCREASED ODDS FOR ABOVE NORMAL PRECIPITATION FOR THE ALASKA PANHANDLE AS WELL AS EASTERN AND CENTRAL MAINLAND ALASKA. NEAR TO BELOW NORMAL PRECIPITATION IS FAVORED BEHIND THE TROUGH FOR EXTREME SOUTHWESTERN MAINLAND ALASKA, THE ALASKA PENINSULA, AND THE EASTERN ALEUTIANS. RIDGING AND NEAR TO ABOVE NORMAL HEIGHTS ENHANCE PROBABILITIES FOR BELOW NORMAL PRECIPITATION FROM PARTS OF THE GULF COAST NORTHWARD TO THE INTERIOR NORTHEAST.  ENHANCED PROBABILITIES FOR NEAR TO ABOVE NORMAL PRECIPITATION ARE INDICATED FOR PARTS OF THE EAST COAST DUE TO POTENTIAL EFFECTS FROM HURRICANES JOSE AND MARIA. UNCERTAINTIES ARE HIGH FOR THIS REGION AND PROBABILITIES ARE SUBJECT TO CHANGE PENDING UPDATED MODEL GUIDANCE.   

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOUT AVERAGE, 3 OUT OF 5, DUE TO GOOD MODEL AGREEMENT ON AN AMPLIFIED FLOW PATTERN OVER MUCH OF THE FORECAST DOMAIN OFFSET BY HIGH UNCERTAINTY ALONG THE EAST COAST WITH RESPECT TO HURRICANES JOSE AND MARIA. 

8-14 DAY OUTLOOK FOR SEP 26 – OCT 02, 2017 

DURING THE WEEK-2 PERIOD, THE OVERALL 500-HPA FLOW IS FORECAST TO DE-AMPLIFY AND TRANSITION TO A MORE PROGRESSIVE PATTERN. THE TROUGH OVER THE WESTERN CONUS DURING THE 6 TO 10 DAY PERIOD IS EXPECTED TO SHIFT EASTWARD TO THE NORTHERN PLAINS/WESTERN GREAT LAKES DURING WEEK-2. BEHIND IT, A RIDGE IS FORECAST TO BUILD OVER THE NORTHWESTERN CONUS WHILE A TROUGH IS INDICATED OVER WESTERN MAINLAND ALASKA. FARTHER TO THE SOUTH, SUBTROPICAL RIDGING IS EXPECTED FOR PORTIONS OF THE SOUTHERN PLAINS. A WEAKNESS IN THE SUBTROPICAL RIDGE IS PREDICTED NEAR THE EAST COAST AND UNCERTAINTY REMAINS ELEVATED AS TO THE EVOLUTION OF HURRICANE MARIA INTO THE WEEK-2 TIME PERIOD. MEAN SURFACE LOW PRESSURE ASSOCIATED WITH MARIA IS FORECAST BY THE ECMWF OR GFS ENSEMBLE MEANS OFF THE MID ATLANTIC OR NORTHEAST COAST. INTERESTS ALONG THE EAST COAST SHOULD CONTINUE TO MONITOR THE LATEST UPDATES REGARDING HURRICANE MARIA DURING THE WEEK-2 PERIOD. 

THERE ARE ENHANCED PROBABILITIES FOR BELOW NORMAL TEMPERATURES FOR MUCH OF THE CENTRAL CONUS IN ASSOCIATION WITH THE TROUGH OVER THE NORTHERN PLAINS / GREAT LAKES. NEAR TO ABOVE NORMAL TEMPERATURES ARE FAVORED AHEAD OF THIS TROUGH FOR MUCH OF THE EASTERN CONUS AND GULF COAST REGION. RIDGING LEADS TO INCREASED ODDS FOR ABOVE NORMAL TEMPERATURES FOR THE WEST COAST OF THE CONUS. ABOVE NORMAL TEMPERATURES ARE ALSO FAVORED FOR PARTS OF EASTERN MAINLAND ALASKA AS WELL AS THE ALASKA PANHANDLE UNDERNEATH EXPECTED ABOVE NORMAL HEIGHTS. NEAR TO BELOW NORMAL TEMPERATURE PROBABILITIES ARE ENHANCED FOR PARTS OF CENTRAL AND WESTERN MAINLAND ALASKA AND THE ALEUTIANS IN ASSOCIATION WITH A TROUGH OVER WESTERN ALASKA. 

THERE ARE ENHANCED PROBABILITIES FOR ABOVE NORMAL PRECIPITATION FOR MUCH OF THE SOUTH-CENTRAL CONUS EXTENDING TO THE WESTERN GREAT LAKES UNDERNEATH CYCLONIC FLOW. ABOVE NORMAL PRECIPITATION IS FAVORED FOR PARTS OF THE NORTHEAST AND MID-ATLANTIC EAST OF THE TROUGH OVER THE NORTH-CENTRAL CONUS AND ALSO DUE TO POTENTIAL EFFECTS FROM HURRICANE MARIA. ENHANCED PROBABILITIES FOR BELOW NORMAL PRECIPITATION ARE INDICATED FARTHER TO THE SOUTH FOR MUCH OF THE SOUTHEASTERN CONUS, CONSISTENT WITH DYNAMICAL MODEL GUIDANCE FROM THE GEFS AND ECMWF ENSEMBLE MEMBERS. RIDGING LEADS TO FAVORED BELOW NORMAL PRECIPITATION FOR THE NORTHWESTERN CONUS. THE TROUGH OVER WESTERN ALASKA LEADS TO INCREASED ODDS FOR ABOVE MEDIAN PRECIPITATION FOR EASTERN MAINLAND ALASKA AND NORTHERN PARTS OF THE PANHANDLE. BELOW MEDIAN PRECIPITATION IS FAVORED FOR PARTS OF WESTERN ALASKA UNDERNEATH MEAN EASTERLY FLOW.    

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD IS: BELOW AVERAGE, 2 OUT OF 5, DUE TO A DE-AMPLIFYING PATTERN AS WELL AS UNCERTAINTIES SURROUNDING THE EVOLUTION  OF HURRICANE MARIA.

THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON  SEPTEMBER 21

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.

Analogs to the Outlook.

Now let us take a detailed look at the “Analogs” which NOAA provides 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 was used in some way to predict the 6 – 14 day Outlook.

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. There is a second set of analogs associated with the Outlook but I have not been regularly analyzing this second set of information. The first set which is what I am using today applies to the 5 and 7 day observed pattern prior to today. The second set, which I am not using, relates to the correlation of the forecasted outlook 6 – 10 days out with similar patterns that have occurred in the past during the dates covered by the 6 – 10 Day Outlook. The second set of analogs may also be useful information but 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.

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

The spread among the analogs from September 4 to September 30 is 26 days about a week more 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, is about September 17. These analogs are centered on 3 days and 4 days ago (September 14 or September 15). So the analogs could be considered to be just a couple of day in advance of the weather that we would normally be getting right now. For more information on Analogs see discussion in the GEI Weather Page Glossary.

There are five ENSO El Nino Modoki Type II analogs (very strange), one Neutral Analog and four La Nina analogs. The phases of the ocean cycles of the analogs are consistent with McCabe Conditions C and D which are opposites but both associated with AMO+. The tend to be dry conditions for most of CONUS. It is strange that these are the most numerous analogs. It is telling us something but I have not had the time today to try to figure this out but it is interesting that we have so many analogs associated with AMO+ at the same time we have such and active Atlantic re cyclones.

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.

Sometimes it is easier to work in black and white especially if you print this report so there is a black and white version from the later report by the same authors. Darker corresponds to red in the color graphic i.e. higher probability of drought.

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.

Looking Out Beyond Three Months

The Seasonal Outlook Update Report was issued in two parts because JAMSTEC was late. Part I which focused on the NOAA forecast comparing the new forecast to the prior forecast can be accessed here and Part II which focused on the comparison between the NOAA forecast and the JAMSTEC forecast can be accessed here. The Part II report was also used to provide updates on Harvey because I can only publish two reports at the same time and be able to update them. 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. There will be a new Seasonal Outlook issued by NOAA on September 21 which we will report on September 23.

Historical Anomaly Analysis

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

Recent CONUS Weather

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

Here is the 30 Days ending September 9, 2017

And the 30 Days ending September 16, 2017

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

Forecast for Today

Additional Maps showing different weather variables can be found here.

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

Temperature

Precipitation

Looking Out a Few Months

Here is the precipitation forecast from Queensland Australia:

JAMSTEC Forecasts

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.

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

And when we look at the current Sea Surface anomalies below, we see a lot of them not just along the Equator related to ENSO.[NOAA may be having problems updating their daily SST Anomaly Report so I am working with the latest version that I have]

First the categorization of the anomalies.

The categorization of the four week change in the anomalies.

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.

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

Now let us look at the Western Pacific in Motion.

C. Progress of ENSO

Starting with Surface Conditions.

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 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.

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.

My Calculation of the Nino 3.4 Index

So as of Monday September 18, in the afternoon working from the September 17 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.

This overlaps with the next topic but I will show it here.

Sea Surface Temperature and Anomalies

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.

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

Let us look in more detail at the Equatorial Water Temperatures.

We are now going to look at a three-dimensional view of the Equator and move from the surface view and an average of the subsurface heat content to a more detailed view from the surface down  This graphic provides both a summary perspective and a history (small images on the right). 

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We are now starting to see the colder water make it far enough west to be in the Nino 3.4 Measurement Area. There is cool water at depth from 165W to 100W so we should expect lower Nino 3.4 readings in the weeks ahead. JAMSTEC it seems is paying attention to that yellow/orange area at about 150E which I gather they believe will this winter record as Neutral with a cool bias but not as cool as NOAA is forecasting.

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 and today in particular, 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.

Here are the above graphics as a time sequence animation. You may have to click on them to get the animation going.

And now Let us look at the Atmosphere.

Low-Level Wind Anomalies near the Equator

Here are the low-level wind anomalies.

And now the Outgoing Long-wave Radiation (OLR) Anomalies which tells us where convection has been taking place. 

And Now the Air Pressure which Shows up Mostly in 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.

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.

Forecasting the Evolution of ENSO

The previously issued on August 18 CPC/IRI fully model-based report is shown on the right The earlier August 10 IRI/CPC Meteorologist survey is shown on the left.

And the updated version.

CPC/IRI ENSO Update

Published: September 14, 2017

El Niño/Southern Oscillation (ENSO) Diagnostic Discussion issued jointly by the Climate Prediction Center/NCEP/NWS and the International Research Institute for Climate and Society

ENSO Alert System Status: La Niña Watch

Synopsis: There is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18.

Over the last month, equatorial sea surface temperatures (SSTs) were near-to-below average across the central and eastern Pacific Ocean (Fig. 1). ENSO-neutral conditions were apparent in the weekly fluctuation of Niño-3.4 SST index values between -0.1°C and -0.6°C (Fig. 2). While temperature anomalies were variable at the surface, they became increasingly negative in the sub-surface ocean (Fig. 3), due to the shoaling of the thermocline across the east-central and eastern Pacific (Fig. 4). Though remaining mostly north of the equator, convection was suppressed over the western and central Pacific Ocean and slightly enhanced near Indonesia (Fig. 5). The low-level trade winds were stronger than average over a small region of the far western tropical Pacific Ocean, and upper-level winds were anomalously easterly over a small area of the east-central Pacific.  Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.

A majority of the models in the IRI/CPC suite of Niño-3.4 predictions favor ENSO-neutral through the Northern Hemisphere 2017-18 winter (Fig. 6). However, the most recent predictions from the NCEP Climate Forecast System (CFSv2) and the North American Multi-Model Ensemble (NMME) indicate the formation of La Niña as soon as the Northern Hemisphere fall 2017 (Fig. 7).  Forecasters favor these predictions in part because of the recent cooling of surface and sub-surface temperature anomalies, and also because of the higher degree of forecast skill at this time of year.  In summary, there is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts are also updated monthly in the Forecast Forum section of CPC’s Climate Diagnostics Bulletin. Additional perspectives and analysis are also available in an ENSO blog.

The next ENSO Diagnostics Discussion is scheduled for 14 September 2017. [Editors Note: NOAA will update next month. IRI will update in a week i.e. September 21, 2017]

Here is the primary NOAA model.

Looking at the forecast today it looks like it would if it happened as forecast be declared to be a La Nina since there would have been at least five overlapping three-month periods with the Nino 3.4 Index being -0.5C or cooler. It is way too soon to draw any conclusions. The estimated current value of the Nino 3.4 Temperature Anomaly after the adjustments have been applied is about -0.3 for the end of August which is ENSO Neutral. But we are starting to see this model flirting with La Nina conditions for a period of time this winter. We have not expected this cool event to last long enough to be declared to be a La Nina but it will be close and it would not take too much to have us change our minds on this.  Click here to see  a month by month version of the same model but without some of the correction methodologies applied. It gives us a better picture of the further out months as we are looking at monthly estimates versus three-month averages. 

From Tropical Tidbits.com

The above is from a legacy “frozen” NOAA system meaning the software is maintained but not updated. Notice since mid-July the collapse of Nino 3.4 values from the range of 0.5C to 0.6C down to Zero C and then down to -0.6C but recently moved back closer to 0C. .

Forecasts from Other Meteorological Agencies.

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

Discussion Issued September 12, 2017 [BOM issues their discussion in three pieces and I have consolidated it into two hopefully not distorting the message]

ENSO neutral, but tropical Pacific continues to cool

Sea surface temperatures (SSTs) have steadily cooled over the central and eastern tropical Pacific for the past two months, but remain well within the neutral ENSO range. Temperatures at and below the surface are now slightly cooler than average. Other indicators of ENSO, such as the Southern Oscillation Index (SOI), cloudiness near the Date Line and trade winds also remain at neutral levels.

International climate models surveyed by the Bureau indicate that ENSO-neutral conditions are likely to persist at least until late 2017. Most models indicate further cooling of the tropical Pacific sea surface temperatures during spring and summer may be likely. However, six out of eight models stay neutral for the remainder of the year, with only two models reaching La Niña thresholds near the end of 2017. Historically this is close to the time when ENSO events peak. 

Here are the July 1 and Aug 1 JAMSTEC Nino 3.4 forecasts side by side.

Here is the new JAMSTEC forecast

Here is the discussion from JAMSTEC:

Sep. 19, 2017 Prediction from 1st Sep., 2017

ENSO forecast:

A weak La Niña-like pattern will persist until boreal spring of next year. Then, the tropical Pacific will return to a normal state by summer.

Indian Ocean forecast:

A positive Indian Ocean Dipole continues to exist as we have predicted but it will disappear by winter. In accord to the positive IOD, sea level anomalies continue to be negative (positive) in the eastern (western) tropical Indian Ocean. The tropical Indian Ocean will return to a normal state by winter.

Regional forecast:

On a seasonal scale, most part of the globe will experience a warmer-than-normal condition, while some parts of western Canada and western U.S. will experience a colder-than-normal condition in boreal fall. In winter, most parts of northern Europe, Russia, northern Canada, southern U.S., Mexico, southern Africa, Southeast Asia, China, and the Far East will experience a warmer-than-normal condition, while some parts of southern Europe, northern Africa, southern Canada, northern U.S., northern Brazil, and Australia will experience a colder-than-normal condition.

As regards to the seasonally averaged rainfall, a wetter-than-normal condition is predicted for some parts of East Africa, India, Philippine, and southern Mexico during boreal fall, whereas most parts of Indonesia, Australia, West Africa, southern Europe, eastern China, western U.S, and western Brazil will experience a drier condition during boreal fall. Those are partly due to the positive Indian Ocean Dipole. In winter, most parts of eastern U.S., Brazil, East Africa, and Australia will experience a wetter-than-normal condition, while some parts of western U.S., Peru, Indonesia, and the northeastern part of South Africa (around Limpopo Province) will experience a drier-than-normal condition.

Most parts of Japan will experience warmer- and wetter-than-normal conditions in fall. However, in late fall and winter, most parts of Japan will experience warmer- and drier-than-normal conditions.

Indian Ocean IOD (It updates every two weeks)

The IOD Forecast is indirectly related to ENSO but in a complex way.

Discussion Issued September 12 [BOM issues their discussion in three pieces and I have consolidated it into two hopefully not distorting the message]

The Indian Ocean Dipole (IOD) is neutral, though index values have generally been weakly positive for the past five months. The weekly index value to 10 September was +0.3 °C, and has persisted at levels just shy of the positive IOD threshold (+0.4 °C) for the past four to six weeks. Most climate models suggest the IOD is likely to remain neutral. However, two of the six climate models surveyed suggest a positive IOD may develop during spring. If a positive IOD eventuated it would likely be short-lived as IOD events typically break down by December as the monsoon trough moves south towards Australia changing wind patterns, which prevents the IOD pattern from being able to form.

Positive IOD events are typically associated with below average spring rainfall, and increased spring–summer fire potential over central and southern Australia, while La Niña-like patterns tend to promote above-average spring rainfall in the south and east. Hence Australia faces some competing, though weak, climate drivers in the months ahead.

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

D. Putting it all Together.

At this time it would seem that the more likely deviation from Neutral right now would be in the direction of a La Nina but we do not believe that there will be a sufficiently long period of La Nina Conditions for a La Nina to be declared but the La Nina Conditions will definitely impact the Boreal Winter.

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.

E. Relevant Recent Articles and Reports

Weather in the News

Hurricane Hype Perhaps

Weather Research in the News

U.S. Main Forecasting Model receives a bad review after Irma

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 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 it is not widely used. 

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

With respect to relating analog dates to ENSO Events, the following table might be useful. In most cases this table will allow the reader to draw appropriate conclusions from NOAA supplied analogs. If the analogs are not associated with an El Nino or La Nina they probably are not as easily interpreted. Remember, an analog is indicating a similarity to a weather pattern in the past. So if the analogs are not associated with a prior El Nino or prior La Nina the computer models are not likely to generate a forecast that is consistent with an El Nino or a La Nina.

ONI Recent History

Four Quadrant Jet Streak Model Read more here This is very useful for guessing at weather as a trough passes through.

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.] 

Re Understanding the Southwest Monsoon this may may come in handy

Great Basin

Source