Winter- Spring – Summer 2018/2019 – Two Very Different Forecasts

Written by Sig Silber

From JAMSTEC

On a seasonal scale, SINTEX-F predicts that most part of the globe will experience a warmer-than-normal condition in boreal winter, while most parts of U.S.A., central Russia, and U.K. will experience a colder-than-normal condition. As regards to the seasonally averaged rainfall in boreal winter, a wetter-than-normal condition is predicted for most part of the western coast of Canada, eastern U.S.A., northeastern Brazil, a central part of the South American Continent, a northeastern part of South Africa, western Europe, and eastern China. 

 In contrast, northwestern/central U.S.A., Central America, a northern part of the South American Continent, northwestern Brazil, Australia, a western part of southern Africa, northern Mozambique, eastern Tanzania, Turkey, a northwestern part of Northern Europe, western Russia, a southern part of Southeast Asia, the Philippines, and a western part of Indonesia 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 co-occurrence of a positive Indian Ocean Dipole and an El Niño/El Niño Modoki-like state.

Two Meteorological Agencies have two very different views of how the winter of 2018/2019 and the following Spring and Summer will play out. Which one has the better handle on the situation. We will know next year. But for now we have two very different forecasts to ponder. NOAA predicts a traditional weak El Nino and we present those maps in this article.

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It is useful to look at the forecasts for the Nino 3.4 Index used to determine if the Sea Surface Temperatures meet the criteria for an El Nino.

	One Year	JAMSTEC Two Years
JAMSTEC
	CFS.v2	CPC-IRI Probabilities
NOAA

We see a lot of difference There may be some difference in duration but there clearly is a difference in both the maximum intensity and the pattern of the intensity with NOAA being lower and more even and JAMSTEC showing a pattern of a rapid rise and rapid decline. The difference in the forecasts shows up in all three seasons. We go into that later in the report. 

Summary: 

This report is organized into a summary that has two tables of graphics that show the temperature and precipitation forecasts for the upcoming three seasons, A brief discussion of the ENSO assumptions by both NOAA and JAMSTEC and then a lengthy analysis which is organized into three parts:

A. A full discussion of the recent NOAA Seasonal Outlook

B. A comparison between the NOAA and JAMSTEC Forecasts.

C. A more detailed analysis of the forecasts for ENSO by NOAA and JAMSTEC and others including the Australian Bureau of Meteorology and other factors influencing the forecasts.

For those who want a quick synopsis of the two forecasts, below is a summary of the temperature and precipitation forecasts for three time-periods and from left to right the NOAA forecast for Alaska and CONUS (the contiguous mid-latitude U.S), then JAMSTEC for North America (which includes Canada and Mexico), and then JAMSTEC for Europe and surrounding areas. Larger graphics are provided later in the report. It is kind of a tease to keep you reading but you can see the evolution of the weather pattern through Fall, Winter and into Spring. For some readers, these two sets of summary graphics may be all the information they wish to look at and that is fine.

Temperature

	NOAA Alaska Plus CONUS	JAMSTEC North America	JAMSTEC Europe
Winter Temp DJF 2018 – 2119
Spring Temp MAM
Summer Temp JJA  2019

Precipitation

	NOAA Alaska Plus CONUS	JAMSTEC North America	JAMSTEC Europe
Winter Precip DJF 2018 – 2119
Spring Precip MAM 2019
Summer Precip JJA 2019

This is a summary of the ENSO Index forecasts of the two agencies. It is somewhat repetitive of the information we provided in the introduction.

The IRI/CPC Model moves into El Nino now and keeps the odds of being in El Nino high before they start to decline in AMJ 2019.	This NOAA CFS.v2 Model keeps us in marginal to almost moderate El Nino through the forecast period but the index is gradually declining.
The IRI/CPC and NOAA CFS.v2 models are pretty much in sync. The IRI/CPC model provides probabilities not intensity so they are not totally comparable. It is the CFS.v2 model that is fairly different from that of JAMSTEC
Looking at the one year forecast, JAMSTEC quickly goes to El Nino values, peaks in Februrary, and then starts to decline but maintains an El Nino level until September 2019. But it is not clear that a declining Nino 3.4 Index produces the same results as a stable index and this has been tested by Queensland re their modeling.	.
Looking at the two year index we see the forecast stablizing at pretty much the transition from ENSO Neutral to marginal La Nina.
I am not sure how to interpret this graphic. It is what JAMSTEC calls their Modoki Index. It is reading lower than their standard index but it is barely in El Nino Territory. It may well impact the Fall of 2019 forecast (not shown) as the Modoki Index does not decline as rapidly as the standard Nino 3.4 Index.

NOAA relies on a variety of forecasts including the CPC/IRI forecast. We did not include the CPC/IRI discussion as we believe it is well covered in the general NOAA discussion shown later.

A part of forecasting is the forecast of Sea Surface Temperatures (SST) as this is very important for many forecasting models.

Updates from JAMSTEC can be found here. Updates from NOAA can be found here. You have to look for the SST row and go to the right where it says “normalized with mask” and click on E3 which provides the latest model run.

A. Focus on the NOAA Update

A note about terminology; the deviations from climatology/normal are color coded but also labeled “A” for more than (above) normal and “B” for less than (below) normal. The area designated EC means Equal Chances of being more or less than normal. JAMSTEC relies on their color coding. In my comments I have used EC to cover all the situations where a clear anomaly is not shown. So the words “warm”, “cool”, “wet”, “dry” should be generally interpreted as being relative to climatology/normal for that location and time of year.

First we will take a look at the NOAA Early Outlook for November 2018. It is called the Early Outlook because it will be updated at the end of October. Only the November Outlook will be updated at that time.

Temperature

Precipitation

We have nothing to compare these maps with as NOAA does not in their Update provide a forecast for each of the subsequent two months separate from their three-month forecast. Thus I do not have previously forecast maps for November from the previous NOAA Report to compare against. And the current month is not over so we can not really compare the forecast for next month against the actual for this month. It is probably best to just try to understand what NOAA is trying to convey about November which for Temperature will be warm in the West and to a lesser extent New England and warm everywhere but with reduced probabilities. Re precipitation, we see for CONUS a wet East Coast and Southern Tier and a dry Northwest.  Alaska is wet with EC in the extreme northeast.

Visual Consistency Testing.

It is useful to see how the month forecast fits with the set of shorter forecasts that we have. But since the Seasonal Outlook was issued on October 18, some of our short term forecast maps fall in October but we include them as they show the trend.

First Temperature

The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts?        →		↑ ←  The full month forecast does not seems to fit well with the 8- 14 day and the Week 3/4 forecast with respect to the Great Lakes area. But, we do not have the last part of the month in the sequence of maps above.

And then Precipitation

The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts?      →		↑ ← The concatenation of the 8-14 Day and Week 3-4 Map seems to fit fairly well. But we do not have the last part of the month in the sequence of maps above.

Now we consider the three-month Outlook.

Notice that the three-month periods are abbreviated e.g. November/December/January  is shown as NDJ. You will see such abbreviations often in this report.

Prior Temperature Outlook for NDJ 2018 – 2019

New Temperature Outlook for NDJ 2018 – 2019

Prior Precipitation Outlook for NDJ  2018 – 2019

New Precipitation Outlook for NDJ 2018 – 2019

It seemed to make sense to have this Australian BOM forecast here. Notice it covers OND not NDJ

.

It is kind of amazing that you can make a worldwide forecast based on just one parameter the SOI and changes in the SOI. Basically it is an ENSO Neutral forecast as the SOI was not changing much during August and September. For CONUS it shows overall dry with a wet Southwest.

Now let us focus on the long-term situation and compare the new set of maps with the maps issued on October 18, 2018.

Prior 14 Month Temperature Outlook: NDJ 2018/2019 – OND 2019

New 14 Month Temperature Outlook: DJF 2018/2019 – NDJ 2019 – 2020

To compare maps from one release to another, one needs to remember that the new release drops one three-month period and adds a later one. So to make the comparisons one has to shift the new maps to the right one position and that makes the map on the right drop down to become the left-most map in the next level. I do not have a computer software tool for doing that for you so you have to do it mentally. When I do the comparison, I print the two sets of maps and put them side by side and number the same three-month maps 1, 2, 3,…..,11 in both sets of maps to make it easier for me to easily compare the same three-month period in the new with the previous forecast. One uses the same procedure to compare the precipitation maps. Based on this procedure, I conclude that:

Now Precipitation

Prior 14 Month Precipitation Outlook: NDJ 2018/2019 – OND 2019

New 14 Month Precipitation Outlook: DJF 2018/2019 – NDJ 2019/2020

If you want larger versions of each map (temperature and precipitation) you can find them here. And then each of those maps can be clicked on to further enlarge them.

Sometimes it is useful to compare the three-month outlook to the forecast for the first of the three months. It shows how much the pattern changes over the three-month period.  

One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.

Below are excerpts (slightly reorganized and with a bit of the redundancy and discussion of methodology removed) from the Discussion released by NOAA on October 18, 2018. Headings that are “Initial Cap” only rather than all caps were added by the Author of this Update Report for clarity. Also we have organized the sequence of the sections of NOAA Discussion to first present the Atmospheric and Oceanic Conditions and then the Initial Month, the Three-month period, and finally the remainder of the 15 Month Forecast. We think that sequence with the three- to four-month period broken out separately, makes the discussion more useful for more readers. NOAA seems to agree as for the second month in a row they have broken out the first three months and we are using that even though it results in redundancy in the rest of the discussion but NOAA  handles that well. We have seen significant improvement in the writing of the NOAA discussion so that makes it better for the reader.

It may not shed much light but the discussion issued with the Week 3 – 4 forecast issued on October 19, 2018 is a bit more current than the discussion with the Seasonal Update but only covers that particular two-week period.

CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS

STARTING WITH OCEAN CONDITIONS, WE CONTINUE TO REMAIN IN ENSO-NEUTRAL CONDITIONS THROUGH EARLY OCTOBER AND THE EL NINO WATCH CONTINUES. IN RECENT WEEKS, HOWEVER, OBSERVATIONS ACROSS THE GLOBAL TROPICS HAVE TRENDED TOWARD MORE FAVORABLE CONDITIONS FOR DEVELOPMENT OF EL NINO IN THE NEXT COUPLE OF MONTHS. SEA SURFACE TEMPERATURES (SSTS) ARE ABOVE-NORMAL ACROSS MOST OF THE EQUATORIAL PACIFIC BASIN, GENERALLY RANGING FROM +0.5 – +1.0 DEGREES C. THE MOST RECENT WEEKLY VALUES OF THE NINO4 AND NINO3.4 INDICES ARE NOW +0.9 AND +0.6 DEGREES C RESPECTIVELY. THIS SOMEWHAT RAPID CHANGE WAS CONSIDERABLY AIDED BY THE DEVELOPMENT OF A WESTERLY WIND BURST (WWB) AND EVOLUTION OF AN ONGOING MJO EVENT AND THE ASSOCIATED WESTERLY LOW-LEVEL WIND ANOMALIES. A STRONG DOWNWELLING OCEANIC KELVIN WAVE WAS INITIATED AS A RESULT OF THIS SIGNIFICANT WEAKENING OF THE PACIFIC BASIN TRADE WINDS DUE TO THESE EVENTS AND CONTINUES TO SHIFT EASTWARD ACROSS THE PACIFIC BASIN AT DEPTH. ACCORDINGLY, THE EQUATORIAL UPPER-OCEAN HEAT CONTENT HAS INCREASED CONSIDERABLY DURING SEPTEMBER AND EARLY OCTOBER MAKING THE DEVELOPMENT OF EL NINO SOMEWHAT MORE LIKELY. SPECIFIC NINO3.4 SST FORECASTS ARE REVIEWED IN THE SECTION BELOW.  

THE ATMOSPHERIC CONDITIONS ASSOCIATED WITH A DEVELOPING EL NINO EVENT REMAIN MODEST AT BEST. ALTHOUGH WESTERLY LOW-LEVEL WIND ANOMALIES ARE NOW PRESENT, ANY ORGANIZED AREAS OF ENHANCED CONVECTION ARE NOT YET PRESENT. THIS IS MOST LIKELY, HOWEVER, IN PART DUE TO THE COUNTER-ACTING EFFECT FROM LARGE SCALE SUBSIDENCE ASSOCIATED WITH THE SUPPRESSED CONVECTIVE PHASE OF THE MJO.  

TURNING TO CURRENT TERRESTRIAL CONDITIONS, WE NOTE MUCH ABOVE-NORMAL SOIL MOISTURE ANOMALIES FROM TEXAS TO THE MIDWEST, EASTWARD TO THE GREAT LAKES, MID-ATLANTIC AND PARTS OF THE NORTHEAST, WHILE DROUGHT CONDITIONS PERSIST ACROSS MANY AREAS OF THE WEST. AS WE ARE ENTERING THE LATE AUTUMN AND WINTER MONTHS, SOIL MOISTURE CONDITIONS, ALTHOUGH NEAR THE 99TH PERCENTILE IN MANY AREAS, IS NOT EXPECTED TO CONTRIBUTE ANY SIGNIFICANT IMPACT TO THE CLIMATE CONDITIONS OVER THE NEXT SEVERAL MONTHS. SNOW COVER ANOMALIES (BOTH NEGATIVE AND POSITIVE) FOR SEPTEMBER AND THE FIRST HALF OF OCTOBER ARE IMPORTANT TO NOTE. SNOWFALL OVER AREAS OF EURASIA AND ALASKA ARE CURRENTLY BELOW-NORMAL IN MANY AREAS, BUT SNOWFALL HAS BEEN SUBSTANTIALLY ABOVE-NORMAL FOR PORTIONS OF CENTRAL AND EASTERN CANADA.

PROGNOSTIC DISCUSSION OF SST FORECASTS

FORECASTS OF THE NINO3.4 SST ANOMALY HAVE NOT CHANGED VERY MUCH OVER THE PAST FEW MONTHS TO FIRST ORDER. THE CPC CONSOLIDATION NINO3.4 SST ANOMALY FORECAST MAINTAINS ITS RECENT PREDICTIONS OVER THE PAST SEVERAL MONTHS WITH A PEAK IN POSITIVE ANOMALY DURING NDJ 2018-2019 OF JUST UNDER +1.0 DEGREE C AND THEN SLOWLY DECREASES OVER THE COURSE OF THE WINTER AND SPRING MONTHS OF 2019, ALTHOUGH THE FORECAST IS TEMPERED BY AN OUTLIER FORECAST FROM THE CCA STATISTICAL MODEL. THIS MODEL FORECAST REMAINS IN ENSO-NEUTRAL TERRITORY THROUGH THE WINTER AND INCREASES THEREAFTER. THE NMME NINO3.4 SST ANOMALY MODEL GUIDANCE ALSO HAS REMAINED CONSISTENT OVER THE PAST FEW MONTHS AND CONTINUES TO INDICATE A SLIGHTLY STRONGER EVENT (ENSEMBLE MEAN PEAKING AND PERSISTING BETWEEN +1.0 – +1.2 DEGREES C) DURING THE WINTER AND SPRING MONTHS. THE OFFICIAL CPC-IRI ENSO OUTLOOK FAVORS EL NINO THIS WINTER AND SPRING AT A GREATER THAN 70% PROBABILITY THROUGH JFM 2019 AND THEN DECREASING TO NEAR 50% BY AMJ 2019.

30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2018

FORECASTS OF AUTUMN CLIMATE ARE ESPECIALLY DIFFICULT, AND THE NOVEMBER 2018 OUTLOOK IS NO EXCEPTION. LOW-FREQUENCY CLIMATE FORCING FROM ENSO IS EXPECTED TO GRADUALLY INCREASE DURING THE NEXT SEVERAL WEEKS, THOUGH THIS HAS LIMITED APPLICATIONS TO THE CURRENT OUTLOOK, ESPECIALLY WITH RESPECT TO TEMPERATURE. THE MJO HAS BEEN ACTIVE OVER THE PAST SEVERAL WEEKS, BUT IS NOT EXPECTED TO PLAY A MAJOR ROLE DURING NOVEMBER – THIS IS DUE TO BOTH UNCERTAIN MJO FORCING ITSELF AS WELL AS ONLY MODEST EXTRATROPICAL TELECONNECTIONS AT THIS POINT IN THE SEASONAL CYCLE. THE FORECAST IS THEREFORE INFORMED FIRSTLY BY A BLEND OF CALIBRATED DYNAMICAL GUIDANCE FROM THE NMME AND STATISTICAL GUIDANCE THAT LARGELY UTILIZES LONG-TERM TRENDS. THIS IS AUGMENTED BY ADDITIONAL DYNAMICAL GUIDANCE FROM THE ECMWF, THE WEEKS 3-4 GUIDANCE, AND THE CURRENT EVOLUTION OF DYNAMICAL MODEL FORECASTS THROUGH THE EXTENDED RANGE (~DAYS 10-16) PERIOD.

Temperature

LONG-TERM TRENDS GENERALLY FAVOR ABOVE-NORMAL TEMPERATURES OVER MUCH OF THE CONUS DURING THIS TIME OF YEAR, STRETCHING FROM THE SOUTHWEST TO THE NORTHEAST, WITH RELATIVE WEAKNESSES IN THE NORTHWEST AND SOUTHEAST, RESPECTIVELY. AT THIS POINT, ENSO TELECONNECTIONS ARE NOT A MAJOR PLAYER IN THE TEMPERATURE FORECAST FOR TWO REASONS: THE CONVECTIVE RESPONSE TO THE DEVELOPING ENSO EVENT HAS BEEN SLOW TO EMERGE TO THIS POINT, AND EVEN IN THE PRESENCE OF A SUBSTANTIAL EVENT THE SIGNAL-TO-NOISE RATIO IS QUITE LOW FOR NOVEMBER (CORRELATIONS NEAR OR LESS THAN 0.2). THE CALIBRATED NMME MODEL OUTPUT FAVORS ABOVE-NORMAL TEMPERATURES OVER NEARLY ALL OF NORTH AMERICA, WITH THE LOWEST PROBABILITIES OVER THE SOUTHEASTERN QUARTER OF THE CONUS. THE CFS HAS CONSISTENTLY BEEN FORECASTING ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE CONUS AND MUCH OF ALASKA, WITH BELOW-NORMAL TEMPERATURES CONFINED TO MUCH OF NORTHEASTERN CANADA. THE AFOREMENTIONED FACTORS POINT TO AN INITIAL ‘FIRST GUESS’ THAT FAVORS ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE FORECAST DOMAIN, WITH THE HIGHEST PROBABILITIES OVER NORTHERN AND WESTERN ALASKA AND PARTS OF THE WESTERN CONUS. HOWEVER, PROBABILITIES ARE TEMPERED BY TWO MAIN FACTORS OVER THE CENTRAL AND EASTERN U.S. FIRST, THE ECMWF IN BOTH ITS LONG-RANGE ENSEMBLE SYSTEM AND EXTENDED RANGE (WEEKS 3-4) SYSTEM FAVOR NEAR- TO BELOW-NORMAL TEMPERATURES CENTERED OVER THE CENTRAL AND SOUTHEASTERN CONUS, AND RUN-TO-RUN CONTINUITY HAS BEEN GOOD IN THIS REGARD.  SECONDLY, THIS APPEARS SUPPORTED BY A FORECAST PATTERN CHANGE OVER THE HIGH LATITUDES TOWARD A NEGATIVE PHASE OF THE NAO/AO DURING THE NEXT WEEK TO 10 DAYS. THE LATEST EVOLUTION OF THE GEFS FROM DAYS 11 TO 16 FAVORS A CONTINUATION OF POSITIVE HEIGHT ANOMALIES OVER NORTHERN LATITUDES AND ANOMALOUS TROUGHING SOMEWHERE OVER THE CENTRAL/EASTERN CONUS HEADING INTO THE VERY BEGINNING OF NOVEMBER. THESE COMPOUNDING FACTORS LEAD TO A REDUCTION IN PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES OVER MOST OF THE CENTRAL AND EASTERN CONUS. HOWEVER, GIVEN THE LARGE SCALE CLIMATE FACTORS AT PLAY, THEY ARE NOT SUFFICIENT TO REVERSE THE SIGN OF THE EXPECTED CLIMATE ANOMALIES.

Precipitation

THE PRECIPITATION FORECAST FOR NOVEMBER 2018 HAS MUCH REDUCED COVERAGE COMPARED TO THE TEMPERATURE OUTLOOK, AS IS EXPECTED GIVEN THE LIMITED PREDICTABILITY FOR THIS TYPE OF FORECAST. THE FORECAST IS INFORMED BY THE DYNAMICAL MODEL CONSENSUS AND NINO 3.4 REGRESSIONS, WHICH JUST ABOUT REVEAL THE SAME GENERAL PATTERN. ABOVE-MEDIAN PRECIPITATION IS FAVORED OVER PARTS OF THE SOUTHERN TIER OF THE CONUS AS WELL AS MUCH OF ALASKA. A MODEST AREA DEPICTING BELOW-MEDIAN PRECIPITATION IS INDICATED OVER THE PACIFIC NORTHWEST AND NORTHERN ROCKIES. AREAS SHOWN IN WHITE LABELED EC DEPICT A FORECAST WHERE THE PROBABILITIES FOR EITHER OF THREE CATEGORIES, BELOW-, NEAR- OR ABOVE-MEDIAN MONTHLY TOTAL PRECIPITATION ARE NOT SIGNIFICANTLY DIFFERENT FROM CLIMATOLOGICAL PROBABILITIES.

BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS

THIS SET OF OUTLOOKS UTILIZED TYPICAL IMPACTS ASSOCIATED WITH EL NINO EVENTS, ALBEIT WITH THE UNDERSTANDING THAT THIS MOST LIKELY WILL BE A WEAK EVENT AND NOTING THE CONFIDENCE IN THIS IMPACTS IN INTENSITY AND LOCATION IS SOMEWHAT LOW.  MOREOVER, IT IS NOTED THAT DUE TO ITS LIKELY WEAK NATURE, THE VARIANCE EXPLAINED IN THE MID-LATITUDES OVER THE EARLY PORTION OF THIS SET OF OUTLOOKS FROM THE TROPICAL PACIFIC COULD VERY WELL BE LOW. OTHER FACTORS FROM BOTH THE TROPICS (E.G., MJO) AND HIGH/POLAR LATITUDES (E.G., AO/NAO, NPO, ETC.) ARE LIKELY TO FAVOR HIGH VARIABILITY OVER THE WINTER AND EARLY SPRING SEASONS AND LIKELY WILL EXPLAIN CONSIDERABLY MORE VARIANCE IN THE UPCOMING SEASONAL MEANS IN TEMPERATURE AND PRECIPITATION.  

LOCAL COASTAL SSTS AND CONSIDERATIONS OF AREAS OF ANOMALOUS SNOWFALL WERE CONSIDERED IN MAKING THE OUTLOOKS.

CONTRIBUTIONS TO THE OUTLOOKS ALSO INCLUDED BIAS-CORRECTED AND CALIBRATED DYNAMICAL MODEL GUIDANCE FROM THE NMME AND IMME ENSEMBLE SUITES (BOTH ENSEMBLE MEAN AND THEIR PARTICIPANT MODELS) THROUGH MAM 2019. EMPIRICAL AND STATISTICAL FORECAST MODELS ALSO PLAYED A LARGE ROLE THROUGHOUT ALL FORECAST LEADS. THESE INCLUDED GUIDANCE FROM A COMBINED ENSO-OCN TOOL, THE CCA, THE CA, AND “BRIDGING” TECHNIQUES. MOREOVER, CONSOLIDATION FORECAST GUIDANCE PRODUCTS FROM STATISTICAL ONLY, DYNAMICAL MODEL ONLY, AND COMBINED STATISTICAL AND DYNAMICAL FORECAST TOOLS WAS HEAVILY UTILIZED. OCN ALSO WAS UTILIZED OFTEN THROUGHOUT THE OUTLOOK LEADS FOR BOTH TEMPERATURE AND PRECIPITATION.  

PROGNOSTIC DISCUSSION OF OUTLOOKS – NDJ 2018 TO NDJ 2019

SUMMARY OF THE OUTLOOK FOR November – December 2018 and January 2019

THIS SECTION OF THE SEASONAL OUTLOOK MESSAGE SUMMARIZES THE FIRST FORECAST IN THE SET, THE NOVEMBER-DECEMBER-JANUARY (NDJ) 2018-2019 SEASONAL OUTLOOK. DESCRIPTION OF THE SUBSEQUENT OUTLOOKS, CLIMATE FACTORS CONSIDERED, AND SPECIFIC FORECAST RATIONALE FOR ALL OUTLOOKS ARE PROVIDED IN THE LAST TWO SECTIONS OF THE MESSAGE.

THE NDJ 2018-2019 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL SEASONAL MEAN TEMPERATURES FOR MUCH OF THE FORECAST DOMAIN TO INCLUDE ALL OF ALASKA AND MOST OF THE WESTERN AND NORTHERN CONTIGUOUS U.S. THE GREATEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE INDICATED FOR WESTERN AND NORTHERN ALASKA AND TO A LESSER DEGREE THE PACIFIC NORTHWEST. FOR SEASONAL TOTAL PRECIPITATION AMOUNTS DURING NDJ 2018-2019, THERE ARE MODESTLY ELEVATED CHANCES OF ABOVE-NORMAL PRECIPITATION FOR MOST OF THE SOUTHERN TIER OF THE CONTIGUOUS U.S., THE CENTRAL EASTERN SEABOARD, AND SOUTHERN ALASKA.

TEMPERATURE

 IN REVIEWING THE FIRST FOUR FORECAST LEADS THROUGH THE WINTER 2018-2019 AND EARLY SPRING MONTHS IN 2019, THE NDJ AND DJF 2018-2019 TEMPERATURE OUTLOOKS ARE SIMILAR AND DEPICT ELEVATED ODDS OF ABOVE-NORMAL TEMPERATURES FOR ALASKA AND MUCH OF THE WESTERN AND NORTHERN CONUS WITH EC NOTED FOR THE SOUTHEAST. AS WE PROGRESS THROUGH THE WINTER INTO THE EARLY SPRING, THE FORECAST SEQUENCE DEPICTS A TENDENCY FOR THE ODDS OF ABOVE-NORMAL TEMPERATURES TO DECREASE ALONG WITH FORECAST COVERAGE FIRST FOR THE OHIO VALLEY AND MID-ATLANTIC AND THEN LATER IN THE GREAT LAKES AND NORTHEAST BY FMA 2019 WHERE EC IS FORECAST. IN  ADDITION, OVER THE SAME TIME, THERE IS AN EASTERN EXPANSION OF ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS THE SOUTHERN PLAINS INTO THE SOUTHEAST CONUS. FOR THESE LEADS, OTHER THAN AREAS IN ALASKA AND THE PACIFIC NORTHWEST, THE PROBABILITIES ARE QUITE MODEST.

THIS DEPICTED EVOLUTION (VARIATION OF AREAS DENOTED AS EC) IN THE FORECAST OF SEASONAL MEAN TEMPERATURES IS A RESULT OF CHANGING AREAS WITH THE GREATEST UNCERTAINTY AND SO LOWER FORECAST CONFIDENCE. UNDERSTANDING THE WEAK NATURE OF EL NINO ANTICIPATED THIS WINTER AND CONFRONTED BY CONSIDERABLE CONFLICTING FORECAST TOOL INFORMATION IN THESE AREAS, EC IS FORECAST AT THIS TIME. DURING NDJ AND DJF 2018-2019, DYNAMICAL MODEL GUIDANCE FROM THE NMME DEPICTS CALIBRATED PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES NEARLY UNANIMOUSLY ACROSS MUCH OF THE NORTH IN AGREEMENT WITH THE AFOREMENTIONED STATISTICAL FORECAST TOOLS AND OBJECTIVE, SKILL WEIGHTED CONSOLIDATION GUIDANCE PRODUCTS.  

AS WE PROGRESS THROUGH THE WINTER, POSITIVE TEMPERATURE TRENDS IN MANY AREAS NO LONGER EXIST AND CALIBRATED DYNAMICAL MODEL GUIDANCE PROBABILITIES DECREASE SUBSTANTIALLY, ALONG WITH LITTLE HISTORICAL FORECAST SKILL INDICATED. AN ADDITIONAL FACTOR IS THAT THE ECMWF SEASONAL PREDICTION FAVORS BELOW-NORMAL TEMPERATURES FOR A CONSIDERABLE AREA THAT STRETCHES FROM THE SOUTHERN PLAINS AND PARTS OF THE SOUTHEAST CONUS IN NDJ 2018-2019 TO AN EXPANDED AREA THAT INCLUDES THE CENTRAL PLAINS, CENTRAL MISSISSIPPI VALLEY, OHIO VALLEY, AND MID-ATLANTIC. MOREOVER, THE ENSO-OCN TOOL AND OBJECTIVE, SKILL WEIGHTED CONSOLIDATION FORECAST TOOLS INDICATE A VARYING MIXTURE OF QUITE MODEST PROBABILITIES FOR EITHER OF THE THREE FORECAST CATEGORIES.

IN ADDITION, UNCERTAINTIES IN THE PREDOMINATE PHASE OF THE AO/NAO AND MJO ACTIVITY ESPECIALLY FROM MID-WINTER INTO EARLY SPRING MAKE A FORECAST OF EC NOT AN UNREASONABLE CHOICE AS VARIABILITY OVERALL IS LIKELY TO BE HIGH AND DEPEND ON CONSIDERABLE IMPACTS ASSOCIATED WITH BOTH TROPICAL AND HIGH LATITUDE SUBSEASONAL VARIABILITY WHICH IS DIFFICULT TO PREDICT AT THESE FORECAST LEADS.  

FOR ALASKA AND THE WESTERN CONUS, THERE IS LITTLE SUPPORT FOR ANY OTHER FORECAST BESIDES ELEVATED ODDS FOR ABOVE-NORMAL TEMPERATURES FOR THIS PORTION OF THE SET OF OUTLOOKS AS WELL AS THE REMAINING OUTLOOKS THROUGH NDJ 2019-2020. THE PRIMARY DRIVER FOR THE OUTLOOKS FROM MJJ 2019 THROUGH NDJ 2019-2020 WERE OCN, ENSO-OCN, AND STATISTICAL OBJECTIVE, SKILL WEIGHTED CONSOLIDATION FORECAST TOOLS.

PRECIPITATION

THE OUTLOOKS FOR SEASONAL TOTAL PRECIPITATION AMOUNTS UTILIZED INFORMATION CONSISTENT WITH AN ANTICIPATED (ALBEIT WEAK) EL NINO EVENT FROM NDJ 2018-2019 THROUGH MAM 2019. DYNAMICAL MODEL GUIDANCE FROM THE NMME AND IMME CONTRIBUTED TO THE OUTLOOKS AS WELL THROUGH MAM 2019. GIVEN THE RANGE OF SOLUTIONS AND GENERALLY WEAK INDICATORS FROM MANY OF THE FORECAST TOOLS, PROBABILITIES FOR EITHER FORECAST CATEGORY (ABOVE- OR BELOW-NORMAL PRECIPITATION) ARE QUITE MODEST, NOT REACHING 50% PROBABILITY FROM THE CLIMATOLOGICAL PROBABILITY OF 33% UNTIL DJF 2018-2019 AND JFM 2019 WHEN A SMALL AREA FAVORING ABOVE-NORMAL PRECIPITATION IS INDICATED FOR AN AREA IN SOUTHERN GEORGIA AND NORTHERN FLORIDA. THIS AREA IS A PART OF A LARGER REGION OF FAVORED ABOVE-NORMAL PRECIPITATION ACROSS THE SOUTHERN TIER OF THE CONUS THROUGH MAM 2019. PRIMARILY SUPPORTED BY DYNAMICAL MODEL GUIDANCE, AN INCREASE IN COVERAGE OF THIS REGION IN THE CENTRAL ROCKIES AND CENTRAL PLAINS DURING JFM AND FMA 2019 IS FORECAST.  

BELOW-NORMAL PRECIPITATION IS FAVORED FOR PARTS OF PACIFIC NORTHWEST AND NORTHERN ROCKIES IN NDJ 2018-2019 AND THEN PRIMARILY CENTERED ACROSS MONTANA DURING JFM AND FMA 2019. SIMILARLY, BELOW NORMAL PRECIPITATION IS FAVORED FOR PARTS OF THE GREAT LAKES AND LATER THE OHIO VALLEY OVER THE SEASONS FROM DJF 2018-2019 TO FMA 2019. EL NINO CONSIDERATIONS AND CONSISTENT DYNAMICAL MODEL GUIDANCE FAVORED ELEVATED ODDS OF ABOVE-NORMAL PRECIPITATION FOR SOUTHERN ALASKA THROUGH FMA 2019. THERE WAS CONSIDERABLE CONFLICTING FORECAST TOOL INFORMATION (SEVERAL SOURCES) FOR THE EARLY LEADS ACROSS CALIFORNIA SO EC WAS INDICATED AT THIS TIME FOR THIS REGION EXCEPT FOR A SMALL AREA IN SOUTHERN CALIFORNIA.

FROM AMJ 2019 THROUGH NDJ 2019-2020, THE OUTLOOKS ARE BASED PREDOMINATELY ON LONG TERM TRENDS AS DIAGNOSED BY OCN FOR EACH FORECAST SEASON. TO THIS END, THE MOST BROAD AND CONSISTENT SIGNALS FOR THIS ARE ELEVATED ODDS FOR BELOW-NORMAL PRECIPITATION IN THE NORTHERN ROCKIES FROM MJJ 2019 THROUGH JAS 2019 AND A LARGER AREA FOR FAVORED ABOVE-NORMAL PRECIPITATION FOR PARTS OF THE GREAT LAKES, NORTHEAST, OHIO VALLEY, AND MID-ATLANTIC FROM MJJ 2019 THROUGH OND 2019.

Week 3-4 Forecast Discussion Valid Sat Nov 03 2018-Fri Nov 16 2018

An interesting circulation setup appears in play for the upcoming Weeks 3-4 outlook. Model guidance has converged on the Arctic Oscillation (AO)/North Atlantic Oscillation (NAO) becoming sharply negative, following a prolonged period in its positive phase. Associated with this evolution is a prominent anomalous ridge over the North Atlantic that is anticipated to persist into the outlook period somewhere south of Greenland or Iceland. Elsewhere, the transition towards El Nino in the Pacific continues to appear likely, while the active phase of the MJO is approaching the Maritime Continent. Whether an active MJO can cross the Maritime Continent is a frequent question in these scenarios, further compounded by adjustments to the equatorial trades and warm pool from the building low frequency state. The resulting forecast looks to primarily leverage the evolving AO, given its e-folding time scale lying within the Weeks 3-4 period and consistent evolution from the Week-2 outlook. The ECMWF model is favored among dynamical model guidance for its AO representation and greatest persistence with the North Atlantic block, given empirical evidence of dynamical models often breaking down these features too rapidly. Also of note is the constructed analogue tool, conditioned upon the observed 200-hPa streamfunction across the Northern Hemisphere, represents a similarly realistic evolution of the extratropical circulation in line with the ECMWF guidance.

The forecast 500-hPa circulation field of the ECMWF model depicts the aforementioned block south of Greenland, with widespread positive height anomalies at the polar latitudes. Upstream of the block, anomalous troughing is forecast to extend from the Northern Plains through New England, shifting closer to the east coast by Week-4. Anomalous ridging over the northeastern Pacific is forecast to approach the West Coast by Week-3, and become established through the Great Basin by Week-4. Across the Pacific, a negative North Pacific Oscillation is forecast with ridging over the Bering Strait and troughing south of the Aleutians. Among the other models, the CFS fails to maintain the negative AO or the North Atlantic block, even by Week-3, which is highly suspect. The JMA maintains the negative AO and North Atlantic block, but retrogrades the block towards the Hudson Bay which results in a warmer (cooler) forecast over the eastern (western) CONUS. Subseasonal experiment models without the CFS feature the North Atlantic block and negative height anomalies along the eastern seaboard and ridge across the West, but also feature a substantial trough in the North Pacific that is much closer to North America than the other guidance.

With a ridge-trough pattern favored across the West and East, respectively, above- and below-normal temperatures are broadly forecast across each region. The highest confidence for above-normal temperatures across the West lies near the Pacific Coast, with the anomalous ridge axis in the vicinity for Week-3 and slightly inland for Week-4. The greatest confidence for below-normal temperatures is across the Midwest, in association with the anomalous trough upstream of the North Atlantic block. Enhanced probabilities for below-normal temperatures are forecast to extend from the Southern Plains northeastward through the interior of New England. Above-normal temperatures are also favored across the Florida Peninsula due to concerns about how far south the colder air associated with the anomalous trough will make it. Anomalous ridging forecast across Alaska, coupled with the relatively warm sea surface temperatures suggesting slow development of sea ice around the state, leads to above-normal temperatures being favored here as well. The largest probabilities for above-normal temperatures in Alaska are near the Gulf of Alaska and Bering Sea, given the relatively warm waters and implications for sea ice growth.

An active storm track is favored across the Gulf and East Coasts, tied to the southern and eastern flanks of the anomalous trough. This yields enhanced probabilities for above-median precipitation for these areas. Odds are also increased for above-median precipitation in southern Alaska, with the storm track shifted northward away from the CONUS, and into Alaska instead. This shifted storm track leads to increased probabilities for below-median precipitation across much of the West, tied to the anomalous ridging anticipated here. Below-median precipitation is also forecast across the Great Plains through the western Great Lakes, given limited moisture availability behind the forecasted trough axis.

Relatively warm and wet conditions continue to be favored across the Hawaiian islands given the anomalously warm sea surface temperatures in the vicinity of the archipelago. Enhanced rainfall is also typically associated with the transition towards El Nino, before drier conditions prevail during the bulk of the wet season.

B. Now we begin our comparison of the NOAA and JAMSTEC Forecasts (Focus on next nine months i.e. three seasons)

In this Update, we compare the JAMSTEC temperature and precipitation forecast maps, which are for the World, with the NOAA temperature and precipitation forecast maps that cover only CONUS and Alaska. We do this primarily for educational purposes.

JAMSTEC works in three-month intervals which correspond to seasons and does not change the selection of months each time they update but does so every three months. At that time they drop one season and add another season further in the future. So for JAMSTEC we now have  Winter (DJF), Spring (MAM), and Summer (JJA)  to work with and we have the corresponding maps from NOAA. NOAA also provides a NDJ 2018 – 2019 map that overlaps Fall and Winter and we discussed that earlier but do not use that map for comparison with JAMSTEC as JAMSTEC only provides three sets of maps and they only change every three months.

I show the NOAA Maps first followed by the JAMSTEC maps. I extract North America from the Worldwide JAMSTEC map and use that to compare with the NOAA Maps. I also extract Europe including parts of North Africa and Western Asia from the Worldwide JAMSTEC maps and include those excerpted maps in the summary table at the beginning of this article.

Winter DJF 2018/2019

Temperature

NOAA

And here is the DJF 2018/2019  temperature forecast for North America that I extracted from the JAMSTEC World Forecast.

And now the JAMSTEC WORLD FORECAST (for this graphic my comments are mostly related to areas other than Alaska and CONUS as those comments appear with the larger graphics above)

Precipitation

NOAA

And here is the DJF 2018/2019 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast.

JAMSTEC WORLD FORECAST

Spring (MAM – 2019)

Temperature

NOAA

And here is the MAM – 2019 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast.

 JAMSTEC WORLD FORECAST

NOAA

And here is the MAM – 2019 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast.

JAMSTEC WORLD FORECAST

Summer  (JJA 2019)

Temperature

NOAA

And here is the JJA 2019 Temperature Forecast for North America that I extracted from the JAMSTEC World Forecast.

JAMSTEC WORLD FORECAST

NOAA

And here is the JJA 2019 Precipitation Forecast for North America that I extracted from the JAMSTEC World Forecast

JAMSTEC WORLD FORECAST

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.

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 three-month average compared to today and that is below. These graphics can be clicked on to enlarge.

Three Month Average Anomaly	Current Anomaly
By this point La Nina is gone neutral conditions prevail	We see shades of red all across the Equatorial Pacific now.

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 east to Land. The temperature threshold for El Nino is currently being met everywhere in the Nino 3.4 Measurement Area and the warm anomaly extends west to 160E and in many places extends down to 250 meters. So this El Nino criteria will be met for some time. But the seems to be a dividing line that defines the end of this El Nino

The 29C Isotherm is now at 170W. The 28C Isotherm at 155W. The 27C Isotherm is at 145W and the 25C Isotherm is now at 120W. The 20C Isotherm no longer reaches the surface but the 23C Isotherm does so at 110W.

Tracking the change over a period of a year

The next graphic basically averages out the anomalies by longitude. It averages the anomalies from the surface down to 300 meters.

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.

…………………………………….170W.|…A….|….B…|…C….|…D….|…E…|120W………………………

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 the history

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. We will discuss this in detail in our Saturday 15 Month Forecast Update (15 months by NOAA, three seasons by JAMSTEC). As you can see the odds for El Nino are high. 

Forecasts from Other Meteorological Agencies.

We have shown the JAMSTEC Index forecasts earlier. Here is their Discussion

Oct. 15, 2018 Prediction from 1st Oct., 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 late winter. This El Niño is more or less of Modoki-type and we need to be careful of its impact that may be different from that of the canonical El Niño.

Indian Ocean forecast:

As predicted earlier, the positive Indian Ocean Dipole (IOD) has actually emerged in July and the amplitude was enhanced in September. The model predicts the positive IOD to continue in fall and quickly decay in winter. In accord to the positive IOD evolution, sea level anomalies are expected to be negative (positive) in the eastern (western) tropical Indian Ocean. We also expect the Ningaloo Niña off the west coast of Australia to continue through winter.

Regional forecast:

On a seasonal scale, SINTEX-F predicts that most part of the globe will experience a warmer-than-normal condition in boreal winter, while most parts of U.S.A., central Russia, and U.K. will experience a colder-than-normal condition.

As regards to the seasonally averaged rainfall in boreal winter, a wetter-than-normal condition is predicted for most part of the western coast of Canada, eastern U.S.A., northeastern Brazil, a central part of the South American Continent, a northeastern part of South Africa, western Europe, and eastern China. In contrast, northwestern/central U.S.A., Central America, a northern part of the South American Continent, northwestern Brazil, Australia, a western part of southern Africa, northern Mozambique, eastern Tanzania, Turkey, a northwestern part of Northern Europe, western Russia, a southern part of Southeast Asia, the Philippines, and a western part of Indonesia 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 co-occurrence of a positive Indian Ocean Dipole and an El Niño/El Niño Modoki-like state.

The model predicts most part of Japan will experience warmer and wetter-than-normal condition in 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 October 9, 2018

El Nino ALERT; positive Indian Ocean Dipole likely underway

The Bureau’s ENSO Outlook has been raised to El Nino ALERT. This means there is approximately a 70% chance of El Nino occurring in 2018-around triple the normal likelihood. Similarly, in the Indian Ocean, a positive Indian Ocean Dipole (IOD) may have started.

When combined, these two events in spring increase the possibility of a dry and warm end to the year. It also raises the risk of heatwaves and bushfire weather in the south, but reduces the risk of tropical cyclone activity in the north.

The tropical Pacific Ocean has warmed in recent weeks due to weakening of the trade winds, while the Southern Oscillation Index has fallen to typical El Nino levels. Models suggest further warming of the Pacific is likely. Four of eight models predict El Nino thresholds will likely be exceeded in the coming months, with another two falling just short.

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

The Indian Ocean Dipole is different than ENSO but there are interactions between the two cycles.

Indian Ocean IOD (It updates every two weeks)

Indian Ocean Dipole outlooks (October 9, 2018)

The Indian Ocean Dipole (IOD) has been displaying signs of a positive IOD event for a number of weeks. The weekly index value to 7 October was +0.58 degC. The IOD index has now remained above the positive IOD threshold value (+0.4 C) for four weeks. Along with warm SST anomalies across most of the northern Indian Ocean and cool anomalies near the Indonesian island of Sumatra, this strongly suggests that a positive IOD event is currently underway; nevertheless, these values need to persist until at least November for this to be considered an event.

Four of the six international climate models surveyed by the Bureau suggest that index values will remain above positive IOD thresholds for the remainder of October. All models expect a return to neutral by December. The IOD typically has little influence on Australian climate from December to April.

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

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

4. The Surface Air Pressure that Confirms the Nino 3.4 Index

And of course Queensland Australia is the official keeper of the SOI measurements.

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).