September 24, 2018 Weather and Climate Report – A Clash of two Seasons

Written by Sig Silber

Updated at 10:20 PM EDT on Tuesday September 25 to reflect the formation of Tropical Event Rosa. Subsequently updated shortly after Midnight EDT September 29, 2018 to include the latest discussion on Typhoon Trami.

In the Pacific, a Fall Pattern is interacting with the declining Summer Pattern even resorting to a Rex Block to attempt to impact lower latitudes than usual for this time of the year. It is not clear which side will prevail over the next two weeks but Summer has only a limited timeframe remaining to be dominant and declining latitudinal reach.

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New storm:

And there is a more serious situation in the Pacific. We show the recently issued discussion later in this report but you can find the latest version of the technical discussion here. 

Back to CONUS although this graphic covers more than CONUS.

We now provide 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 deamplifying in what NOAA calls Week – 2		↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems feasible.

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 but deamplifying pattern. It may be shifting to the east a bit.		↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems to be feasible for the Southeast but a bit more problematic for the Northwest but certainly possible.

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 there has been more activity north of CONUS than directly in CONUS.

Tonight, Monday September 24, 2018, as I am looking at the above graphic, of most interest is the Low off the West Coast.

This 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

Additional useful forecasts from the Storm Prediction Center and be found here.  Explanation of symbols can be found here.

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.

Big changes. When I look at this Day 7 forecast, we see the Hawaiian High weak and way out to sea mostly off the chart with surface central pressure of 1016 hPa. The Aleutian Low is strong with surface central pressure of 996hPa and it is located over the western Aleutians but extends all the way to the Northwest coast of CONUS. To the northeast, there is a huge Western Canadian High with surface central pressure of 1024 hPa. Further east, over Greenland there is a High with surface central pressure of 1016 hPa. North of Hudson Bay there is a Low with surface central pressure of 1004 hPa. We can not locate the Bermuda High but there is a Low offshore with surface central pressure of at 1004 hPa. There is another High over the Mid-Atlantic with surface central pressure of 1024 hPa. The Four Corners High is subsumed into the Western Canadian High..yes that is what I have just written. To the southwest of where we would normally look for the Four Corners High there is a low and an inverted trough entering from Mexico with surface central pressure of 1008 hPa. More on this in the Tropical section of this report.

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
.You can see that trough from the Pacific	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 24, 2018 was 4 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on September 24, 2018 was 4 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 24, 2018 was 4 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on September 24, 2018 was 4 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today September 24 and the Week 3 – 4 discussion issued on September 21

6-10 DAY OUTLOOK FOR SEP 30 – OCT 04, 2018  

TODAY’S MODELS ARE IN GENERALLY GOOD AGREEMENT ON THE OVERALL 500-HPA GEOPOTENTIAL HEIGHT PATTERN FORECAST DURING THE 6-10 DAY PERIOD. A DEEP TROUGH IS FORECAST OVER THE BERING SEA, WHILE A STRONG, VERY ANOMALOUS RIDGE IS FORECAST OVER MAINLAND ALASKA. DOWNSTREAM A TROUGH IS PREDICTED NEAR THE WEST COAST OF THE CONUS, AND SOME RIDGING IS FORECAST TO PERSIST OVER THE EASTERN CONUS. TODAY’S MANUAL 500-HPA HEIGHT BLEND IS BASED PRIMARILY ON THE ENSEMBLE MEANS FROM THE EUROPEAN, GEFS, AND CANADIAN MODEL SUITES. 

LARGE POSITIVE HEIGHT ANOMALIES OVER ALASKA STRONGLY FAVOR ABOVE NORMAL TEMPERATURES FOR THE ENTIRE STATE. PREDICTED RIDGING AND POSITIVE 500-HPA HEIGHTS LEAD TO ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES OVER MOST OF THE SOUTHERN AND EASTERN CONUS. BELOW NORMAL TEMPERATURES ARE FAVORED OVER NORTHERN AND CENTRAL CALIFORNIA, AND OVER THE PACIFIC NORTHWEST EXTENDING EASTWARD TO WISCONSIN, CONSISTENT WITH THE REFORECAST-CALIBRATED GEFS AND ECMWF TOOL. 

THE DEEP TROUGH PREDICTED OVER THE BERING SEA INCREASES THE LIKELIHOOD OF ABOVE NORMAL PRECIPITATION FOR WESTERN ALASKA AND THE ALEUTIANS, WHILE THE STRONG RIDGE PREDICTED OVER ALASKA FAVORS BELOW NORMAL PRECIPITATION OVER EASTERN ALASKA AND THE ALASKA PANHANDLE. THE TROUGH NEAR THE WEST COAST AND SOUTHWESTERLY FLOW INCREASE CHANCES OF ABOVE NORMAL PRECIPITATION OVER MOST OF THE CONUS, CONSISTENT WITH CALIBRATED PRECIPITATION FROM THE GFS AND ECMWF ENSEMBLE FORECASTS.

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO FAIRLY GOOD AGREEMENT AMONG THE MODELS AND TEMPERATURE TOOLS AND A WELL-DEFINED HIGHLY AMPLIFIED PATTERN, OFFSET SLIGHTLY BY SOME DIFFERENCES BETWEEN THE PRECIPITATION TOOLS.

8-14 DAY OUTLOOK FOR OCT 02 – 08 2018 

DURING THE WEEK-2 PERIOD, THE 500-HPA HEIGHT PATTERN OVER THE FORECAST DOMAIN IS EXPECTED TO BE FAIRLY SIMILAR TO THE 6-10 DAY PERIOD, THOUGH WITH WEAKER PREDICTED HEIGHT ANOMALY VALUES OVER THE CONUS.  RIDGING IS ALSO EXPECTED TO WEAKEN OVER ALASKA. TODAY’S WEEK-2 MANUAL 500-HPA HEIGHT BLEND IS BASED PRIMARILY ON THE ENSEMBLE MEAN SOLUTIONS WITH THE GREATEST WEIGHT GIVEN TO THE 0Z ECMWF ENSEMBLE. 

THE TEMPERATURE PROBABILITY FORECAST FOR WEEK-2 IS SIMILAR TO THE 6-10 DAY PERIOD, EXCEPT THAT NEAR NORMAL TEMPERATURES ARE FAVORED OVER THE WEST COAST OF THE CONUS. THE PRECIPITATION PROBABILITY FORECAST FOR WEEK-2 IS ALSO SIMILAR TO THE 6-10 DAY PERIOD, EXCEPT THAT NEAR TO BELOW NORMAL PRECIPITATION IS FORECAST OVER PARTS OF THE PACIFIC NORTHWEST AND ABOVE NORMAL PRECIPITATION IS PREDICTED OVER ENTIRE EAST SEABOARD. 

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO FAIRLY GOOD AGREEMENT AMONG THE MODELS AND TEMPERATURE TOOLS AND A WELL-DEFINED HIGHLY AMPLIFIED PATTERN, OFFSET SLIGHTLY BY SOME DIFFERENCES BETWEEN THE PRECIPITATION TOOLS.

Week 3-4 Forecast Discussion Valid Sat Oct 06 2018-Fri Oct 19 2018

ENSO-neutral conditions currently are present across the equatorial Pacific Ocean. Equatorial sea surface temperatures (SSTs) are near to above average across most of the Pacific Ocean. The CPC velocity potential based and RMM MJO indices indicate an inactive MJO. The GEFS depicts the MJO to strengthen and emerge over the Western Hemisphere during the next two weeks. The Week 3-4 temperature and precipitation outlooks rely primarily on dynamical model forecasts from the NCEP CFS, the ECMWF, and the JMA operational ensemble prediction systems, as well as forecasts from the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of experimental ensemble prediction systems. Consideration is also given to the possible evolution of the predicted circulation pattern for Week-2.

Dynamical model guidance from the CFS and ECMWF is broadly consistent, depicting a trough over the Aleutians, while a strong ridge is forecast over Mainland Alaska and along the Pacific Northwest of the CONUS. Downstream a trough is centered over parts of the Upper Midwest and Great Lakes region, and ridging is forecast to persist in parts of the Southeast. The CFS and ECMWF ensemble means favor near-normal 500-hPa heights over Hawaii, while JMA favors above-normal 500-hPa heights there.

Ridging and large positive 500-hPa heights over Alaska lead to enhanced probabilities of above-normal temperatures over the entire state. Dynamical model forecasts (CFS, ECMWF and JMA) are in general agreement on increased chances of above-normal temperatures for the western CONUS and parts of the Southeast. Below-normal temperatures are favored over the Southern Plains, the Lower Mississippi Valley, and the Tennessee Valley, extending northeastward across the Middle and Upper Mississippi Valley, the Ohio Valley, the Middle Atlantic, the Great Lakes region, and over the Northeast, consistent with dynamical model guidance from SubX.

The various model guidance is in fairly good agreement on the precipitation outlook for the Week 3-4 period. Forecast ridging across the Pacific Northwest supports increased chances of anomalously dry conditions for the northwestern CONUS. The greatest probabilities for above-normal precipitation are indicated over the Pacific Northwest. Above-normal precipitation is favored across the southeastern seaboard, consistent with dynamical model predicted Week 3-4 precipitation amounts. Above-normal precipitation is likely in southern Alaska and the Alaska Panhandle due to troughing over the Aleutians.

Persistent positive SST anomalies continue to surround Hawaii, supporting increased chances of above-normal temperatures and precipitation across the island chain. Dynamical model precipitation forecasts generally favor above-normal rainfall over Kahului and Honolulu.

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. 

First 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.

 First.

And then

This tool allows one to translate the location of the forecast MJO to the impacts on CONUS. To make it easier for the reader I am displaying the highest probability interpretation for the time period in question namely August/September/October. This (70% match) of course might miss some other impacts which have less statistical confirmation but may none-the-less be valied.

Remember we are interested in Phase 8 as it impacts CONUS weather during August September and October. So that is what I have displayed.

Temperature

Precipitation

I can not display it in the article but this is another link to an application that allows you to figure out the lagged impacts on temperture of the MJO. There is a lot of statistical analysis available to predict the impacts of the MJO which is different from predicting the location of the MJO.

Analogs to the NOAA 6 – 14 Day 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. * Index reads positive for that month but that was a period of time that was generally PDO Negative.

The spread among the analogs from September 8 to October 7 is 29 days which is about the same as 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 23. These analogs are centered on 3 days and 4 days ago (Sept 20 or September 21). So the analogs could be considered to be pretty much 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 four El Nino Analogs, five Neutral analogs and one La Nina Analog. The pre-forecast analogs this week are supportive of McCabe A and B and not less supportive of McCabe D. This combination is fairly consistent with the NOAA forecast except that McCabe A and McCabe B are opposites with respect to the West in terms of whether the north or the south is dry (and there are other differences as well). Many of the analogs are associated with AMO Negative.

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 15, 2018	And the 30 Days ending September 22, 2018
A change is the cool anomaly along the Western Northern Tier. The warm anomaly extends further south. The wet anomaly extends further east. We will start to see the impact of Florence next week.	We see the impact of Florence but it is less than one might have expected. The Temperature anomalies are more extreme especially in the East.
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 Late 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

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 July and August. Of interest is the generally dry Western CONUS and relatively dry Europe

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 western Mediterranean is warm So is the western Black Sea It is warm off Somalia	Warm around Kamchatka Slightly warm around Japan	Very warm Chukchi Sea, Bering Strait and Bering Sea Warm offshore of Alaska Panhandle It is pretty impressive. Warm off Baja	Hudson Bay cool Great Lakes Warm Cool west of the British Isles way south of Greenland. Slightly warm offshore of Nova Scotia down to Cape Hatteras extending far out to sea Slightly warm northern Gulf of Mexico	Warm north of Scandinavia
Equator	Still looks like Neutral. May be able to detect the upwelling of the Kelvin Wave off Ecuador.
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cool off west coast of Africa north of the  Equator. Cool south of Gulf of Guinea Warm between Mozambique and Madagascar.	Very Cool	Cool to the northwest Cool to the south and southwest	Warm down to Peru	Warm off Venezuela Warm off 20S to 40S

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
Mediterranean and Black Sea is mostly Neutral. Southern Caspian Sea is warming. Extreme Cooling in the Arabian Sea	Cooling north of Japan but warming east and south of Japan.	Warming in Bering Sea Warming around and south of Alaska. Very intense south of the western end of the Aleutians. Cooling west of Baja.	Cooling southern end of Hudson Bay Cooling Davis Straits and Nova Scotia Warming east of Southeast Coast Warming east of South America along the Equator.	Significant cooling around British Isles and further to the northwest.
Equator	Eastern Pacific showing a mixed pattern but I see more red than previously.
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cooling west of North Africa. Warming Gulf of Guinea Cooling west of Africa south of the Gulf of Guinea Sight cooling south of Africa.	Cooling but mostly to the Northwest and Southwest	Slight cooling to the Northeast and to the south and southeast	Warm especially 20S to	Warming offshore at the Equator Warming offshore at 40S

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

Atlantic

Tropical Weather Outlook NWS National Hurricane Center Miami FL 800 PM EDT Mon Sep 24 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Subtropical Storm Leslie, located about 1200 miles west of the Azores.

1. A broad area of low pressure located about 400 miles south-southeast of Cape Hatteras, North Carolina, continues to produce disorganized showers and thunderstorms. Environmental conditions are expected to become slightly more conducive for development, and a tropical depression could form tonight or Tuesday while the system moves west-northwestward to northwestward. By Tuesday night and Wednesday, upper-level winds are expected to increase and limit the chances for additional development while the system moves northward near the southeastern United States coast. Regardless of tropical cyclone formation, this system will likely enhance rainfall across portions of northeastern South Carolina and eastern North Carolina Tuesday and Tuesday night. In addition, dangerous surf conditions and rip currents are expected along portions of the North Carolina coast on Tuesday. For more information, please see products from your local National Weather Service office.

* Formation chance through 48 hours…medium…50 percent.

* Formation chance through 5 days…medium…50 percent.

2. A tropical wave, the remnants of Kirk, is located about 1300 miles east of the Windward Islands. This system continues to produce a large area of showers and thunderstorms, along with winds to gale force over the northern portion of the wave, while it moves quickly westward at around 25 mph. This system could redevelop into a tropical cyclone during the next few days before it encounters highly unfavorable upper-level winds while it approaches the Caribbean Sea. For more information on this system, see High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours…medium…50 percent.

* Formation chance through 5 days…medium…50 percent.

3. Subtropical Storm Leslie is expected to become post-tropical Tuesday night or Wednesday after it merges with a cold front over the central Atlantic. After that time, Leslie could reacquire some subtropical or tropical characteristics by the end of the week as it meanders over the central Atlantic.

* Formation chance through 48 hours…low…near 0 percent.

* Formation chance through 5 days…medium…50 percent.

High Seas Forecasts issued by the National Weather Service can be found under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and on the Web at https://ocean.weather.gov/shtml/NFDHSFAT1.shtml.

Eastern Pacific

Tropical Weather Outlook NWS National Hurricane Center Miami FL 500 PM PDT Mon Sep 24 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. Showers and thunderstorms associated with a low pressure system located around 300 miles south-southwest of Manzanillo, Mexico continue to show signs of organization.  Environmental conditions appear conducive for further development, and a tropical depression is likely to form within the next day or so while the system moves west-northwestward, well offshore of the coast of Mexico.

* Formation chance through 48 hours…high…90 percent.

* Formation chance through 5 days…high…90 percent.

2. A trough of low pressure located about 1600 miles south-southeast of Hilo, Hawaii is producing disorganized shower activity.  Some gradual development of this system is possible through the end of this week while it moves westward into the eastern portion of the central Pacific.

* Formation chance through 48 hours…low…near 0 percent.

* Formation chance through 5 days…low…30 percent.

Updated information on Atlantic and Eastern Pacific Storms can be found here.

Central Pacific

Additional information can be obtained here.

Western Pacific

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.

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. This animation covers both areas.

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.

The new storm is TRAMI. The information will update automatically as long as the Joint Typhoon Warning Center believes it is appropriate to do so.

WDPN31 PGTW 290300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 34//RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.

   TYPHOON (TY) 28W (TRAMI), LOCATED APPROXIMATELY 85 NM SOUTHWEST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE SYSTEM REMAINS EXPANSIVE AND HAS MAINTAINED A VERY LARGE 81-NM RAGGED EYE. THE INITIAL POSITION IS BASED ON THE EYE FEATURE AND ON A TIGHTLY GROUPED CLUSTER OF 281800Z AGENCY AND RADAR POSITION FIXES WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 90 KNOTS IS BASED ON EQUIVALENT DVORAK ESTIMATES OF T5.0/90 KNOTS FROM PGTW AND KNES. ENVIRONMENTAL ANALYSIS INDICATES THAT TY 28W IS STILL IN LOW (5 TO 10 KNOT) VERTICAL WIND SHEAR (VWS) AND EXCELLENT RADIAL OUTFLOW. SEA SURFACE TEMPERATURES ALSO REMAIN FAVORABLE AT 28 TO 29 CELSIUS. THE CYCLONE IS TRACKING ALONG THE WESTERN EDGE OF THE SUBTROPICAL RIDGE (STR) TO THE EAST.

3. FORECAST REASONING.

   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.

   B. TY TRAMI WILL HAS CRESTED THE STR AXIS AND WILL BEGIN TO ACCELERATE NORTHEASTWARD, MAKING LANDFALL ALONG THE SOUTHWEST COAST OF HONSHU, JAPAN, SHORTLY AFTER TAU 30. THE SYSTEM WILL QUICKLY DRAG ACROSS HONSHU AND BY TAU 48, WILL BE BACK ON THE PACIFIC OCEAN EAST OF MISAWA. THE INITIAL EXPOSURE TO THE STRONG WESTERLIES ASSOCIATED WITH AN APPROACHING MID-LATITUDE TROUGH, IN ADDITION TO THE AFOREMENTIONED FAVORABLE CONDITIONS, WILL FUEL SLIGHT INTENSIFICATION TO 100 KNOTS BY TAU 24. AFTERWARD, INCREASING VWS PLUS INTERACTION WITH THE JAPANESE ISLANDS WILL LEAD TO GRADUAL DECAY. CONCURRENTLY, THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION  AROUND TAU 36 AND BY TAU 48, WILL BECOME A STORM-FORCE COLD CORE LOW WITH AN EXPANDING WIND FIELD. DYNAMIC MODEL GUIDANCE IS IN VERY TIGHT AGREEMENT;  THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//

Here is a recent discussion. We do not plan to routinely update this discussion by you can find it here

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 extending to 100W. Most of this is at depth. One can see why the models predict an El Nino.

The 28C Isotherm is now at 165W, the 27C Isotherm is at 150W, the 25C Isotherm is now at 130W. The 20C Isotherm no longer reaches the surface but the 21C Isotherm does so at 105W.

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 24, in the afternoon working from the September 23 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 a number that rounds up to +0.5 so it is still an ENSO Neutral value. NOAA has again reported the weekly Nino 3.4 to be +0.3 which is an ENSO Neutral value. Nino 4 is reported to be a bit cooler than last week at +0.4. Nino 3 is reported to be warner at +0.2. Nino 1 + 2 which extends from the Equator south rather than being centered on the Equator is reported cooler at -0.1 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.

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.

The discussion released with the forecast follows. It can also be found here.

IRI Technical ENSO Update

Published: September 19, 2018

Note: The SST anomalies cited below refer to the OISSTv2 SST data set, and not ERSSTv4. OISSTv2 is often used for real-time analysis and model initialization, while ERSSTv4 is used for retrospective official ENSO diagnosis because it is more homogeneous over time, allowing for more accurate comparisons among ENSO events that are years apart. During ENSO events, OISSTv2 often shows stronger anomalies than ERSSTv4, and during very strong events the two datasets may differ by as much as 0.5 C. Additionally, the ERSSTv4 may tend to be cooler than OISSTv2, because ERSSTv4 is expressed relative to a base period that is updated every 5 years, while the base period of OISSTv2 is updated every 10 years and so, half of the time, is based on a slightly older period and does not account as much for the slow warming trend in the tropical Pacific SST.

Recent and Current Conditions

In mid-September 2018, the NINO3.4 SST anomaly showed neutral ENSO conditions. For August the SST anomaly was 0.30 C, indicating neutral conditions, and for Jun-Aug it was 0.27 C, also neutral. The IRI’s definition of El Niño, like NOAA/Climate Prediction Center’s, requires that the SST anomaly in the Nino3.4 region (5S-5N; 170W-120W) exceed 0.5 C. Similarly, for La Niña, the anomaly must be -0.5 C or less. The climatological probabilities for La Niña, neutral, and El Niño conditions vary seasonally, and are shown in a table at the bottom of this page for each 3-month season. The most recent weekly anomaly in the Nino3.4 region was 0.3, showing neutral conditions. Additionally, most of the key atmospheric variables, including the upper level zonal wind anomalies, the outgoing longwave radiation pattern (convection), and the Southern Oscillation Index suggest neutral conditions over recent weeks. However, during the most recent month the low-level zonal wind anomalies have become weakly westerly, suggesting a tendency toward El Niño conditions. The subsurface temperature anomalies across the eastern equatorial Pacific remain at moderately above-average, and have recently shown a slight further increase. These warmed waters at depth have been impacting the surface, resulting in slightly above-average temperatures, and also presaging likely further warming of the SST in the coming months. Given the current and recent SST anomalies, the subsurface profile and the conditions of most key atmospheric variables, we see a likely warming to at least weak El Niño conditions beginning in the Sep-Nov period.

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued approximately one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it gave a 50-55% chance for El Niño development during fall season, rising to 65-70% for winter 2018-19. An El Niño watch remains active. The latest set of model ENSO predictions, from mid-September, now available in the IRI/CPC ENSO prediction plume, is discussed below.

As of mid-September, about 60-65% of the dynamical or statistical models predict El Niño conditions for the initial Sep-Nov 2018 season, with about 35-40% showing neutral conditions. Following that first forecast season, probabilities for neutral drop to roughly the 15-30% range for Oct-Dec 2018 through May-Jul 2019. Meanwhile, the probability for El Niño rises to 80-85% for Oct-Dec through Dec-Feb, but remains at more than 70% through to the final forecast season of May-Jul 2019. This hints at the possibility of a 2-year El Niño period, given the late start to the predicted 2018-19 El Niño. La Niña probabilities are near zero throughout the forecast period. At lead times of 3 or more months into the future, statistical and dynamical models that incorporate information about the ocean’s observed subsurface thermal structure generally exhibit higher predictive skill than those that do not. For the Dec-Feb 2018-19 season, among models that do use subsurface temperature information, 23% of models predicts neutral conditions and 77% predict El Niño conditions.

Note  – Only models that produce a new ENSO prediction every month are included in the above statement.

Caution is advised in interpreting the distribution of model predictions as the actual probabilities. At longer leads, the skill of the models degrades, and skill uncertainty must be convolved with the uncertainties from initial conditions and differing model physics, leading to more climatological probabilities in the long-lead ENSO Outlook than might be suggested by the suite of models. Furthermore, the expected skill of one model versus another has not been established using uniform validation procedures, which may cause a difference in the true probability distribution from that taken verbatim from the raw model predictions.

An alternative way to assess the probabilities of the three possible ENSO conditions is more quantitatively precise and less vulnerable to sampling errors than the categorical tallying method used above. This alternative method uses the mean of the predictions of all models on the plume, equally weighted, and constructs a standard error function centered on that mean. The standard error is Gaussian in shape, and has its width determined by an estimate of overall expected model skill for the season of the year and the lead time. Higher skill results in a relatively narrower error distribution, while low skill results in an error distribution with width approaching that of the historical observed distribution. This method shows probabilities for La Niña at 2% or less for the full range of seasons from Sep-Nov 2018 through to May-Jul 2019. Probabilities for neutral conditions begin at 45% for Sep-Nov, fall to about 25-30% for Nov-Jan through Apr-Jun, and are 36% for May-Jul. Probabilities for El Niño, which begin at 55% for Sep-Nov, rise to about the 70-75% range from Nov-Jan through Apr-Jun and drop to 62% for May-Jul. A plot of the probabilities generated from this most recent IRI/CPC ENSO prediction plume using the multi-model mean and the Gaussian standard error method summarizes the model consensus out to about 10 months into the future. The same cautions mentioned above for the distributional count of model predictions apply to this Gaussian standard error method of inferring probabilities, due to differing model biases and skills. In particular, this approach considers only the mean of the predictions, and not the total range across the models, nor the ensemble range within individual models.

In summary, the probabilities derived from the models on the IRI/CPC plume describe, on average, a a tilt of the odds toward El Niño conditions starting from Sep-Nov and continuing through May-Jul 2019, peaking around 70-75% from Nov-Jan through Apr-Jun. The predicted continuation of elevated chances for  El Niño well into spring/early summer 2019 hints at the possibility of a two-year El Niño episode, likely related to the late predicted onset of El Niño in 2018. Probabilities for La Niña are less than 5% throughout the entire forecast period. A caution regarding this latest set of model-based ENSO plume predictions, is that factors such as known specific model biases and recent changes that the models may have missed will be taken into account in the next official outlook to be generated and issued early next month by CPC and IRI, which will include some human judgment in combination with the model guidance.

This graphic shows a collection of models used by various meteorological agencies to forecast the NINO 3.4 Index. We will have an update on this on Thursday and it will be in our Saturday Seasonal Outlook article.

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.

Here is the JAMSTEC discussion which just came out today or tonight. .

Sep. 25, 2018  Prediction from 1st Sep., 2018

ENSO forecast:

The SINTEX-F continues to predict a moderate-to-strong El Niño event that may emerge in 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 during July. In particular, we can see the cold sea surface temperature in the eastern pole clearly. The model predicts the positive IOD to continue during 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 boreal fall and winter seasons 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, SINTEX-F predicts that most part of the globe will experience a warmer-than-normal condition in fall, while some parts of South Africa, southern Russia, U.K. West Africa, and northern Canada will experience a cooler-than-normal condition. In winter, most part of the globe will be in a warmer-than-normal condition, while eastern Australia, northern Africa, Europe, and western China 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 part of western Canada, southwestern/eastern U.S.A., and West Africa. In contrast, northwestern/central U.S.A., Brazil, East Africa, eastern Europe, western Russia, 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 experience extremely drier than normal condition, 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 southern Brazil, U.K., southern India, Southeast Asia, the Philippines, western Indonesia and Australia. On the other hand, most parts of U.S.A, northern Brazil, western South America continent, northern South Africa, Europe, West Asia, and southern China will be wetter-than-normal.

The model predicts most part of Japan will experience warmer and drier-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 25, 2018

El Niño WATCH continues; signs of a positive Indian Ocean Dipole emerge

The El Niño–Southern Oscillation (ENSO) remains neutral. While climate models suggest some easing in the chance of El Niño in 2018, half of the surveyed models still indicate an event is possible. When assessed with current observations, the Bureau’s ENSO Outlook therefore remains at El Niño WATCH, meaning the chance of El Niño in 2018 remains around 50%; double the normal likelihood.

Oceanic and atmospheric indicators of ENSO are generally neutral. While sub-surface waters have recently warmed, sea surface temperatures in the tropical Pacific Ocean are only slightly above average. Likewise, the Southern Oscillation Index remains weakly negative, and short of El Niño levels. Trade winds have recently been weaker than usual in the western Pacific, and may remain weak in the coming weeks. Weakened trade winds can be a precursor to El Niño development.

Climate models now indicate less warming of the tropical Pacific is likely compared with last month. As a result, fewer models now predict an El Niño in 2018—only three of eight models exceed El Niño thresholds in 2018, and a fourth does so in early 2019. The rest remain neutral. 

A positive IOD and El Niño during spring typically means below average rainfall for southern, eastern and central Australia. When a positive IOD and El Niño occur together, the reduction in rainfall is often more widespread.

El Niño onset during December would be later than usual, although not unprecedented.

Indian Ocean IOD (It updates every two weeks)

Indian Ocean Dipole Outlook  Discussion Issued September 25, 2018

Indian Ocean Dipole outlooks

The Indian Ocean Dipole (IOD) is currently neutral. The weekly index value to 23 September was +0.87 °C. The index value climbed steeply during September, and has been above +0.8 ºC now for two weeks.

Four of the six international climate models surveyed by the Bureau suggest that index values will remain above positive IOD thresholds into October, so this may be the start of a positive IOD event. It would take several more weeks of values above thresholds for a positive IOD event to be considered established. All but one model anticipates values will return to neutral for December.

A positive IOD event typically reduces spring rainfall in central and southern Australia, and can exacerbate any potential El Niño driven rainfall deficiencies.

The IOD typically has little influence on Australian climate from December to April.

It is useful to understand where the IOD is measured. This is shown in the below graphic.

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 values and this graphic is probably more useful than the static readings I have provided in the  past. One can see the pattern here better. .

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.

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.