May 22, 2021 Seasonal Forecasts: Part II, NOAA Comparison with JAMSTEC

Written by Sig Silber

We published the NOAA Long-Term Forecast Part I on May 20, 2021. Tonight we compare the NOAA forecast for Alaska and CONUS with the JAMSTEC forecast. It is easier to see the agreement and disagreement by comparing the maps which we show side by side in a table with a summary of the comparison. Obviously, the farther out you look, the less confidence you have in the forecasts and thus the differences in the forecasts. Also provided are the JAMSTEC World Forecasts. JAMSTEC has sent us their forecast privately as their website is still not functional and what they have sent us includes a monthly forecast for each of the first three months so we are also able to compare the NOAA and JAMSTEC June forecasts this time. As usual, there are some significant differences between the two forecasts but also a lot of agreement.

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C. Comparison of the NOAA and JAMSTEC Forecasts

Below is the comparison of the NOAA and JAMSTEC temperature and precipitation forecast maps for the month of June and then three time-periods and from left to right the NOAA forecast for Alaska and CONUS (the contiguous mid-latitude U.S) and then JAMSTEC for North America (which includes Canada and part of Mexico). The NOAA forecast maps can be clicked on to enlarge. The JAMSTEC maps in the table are not set up to be clicked on to enlarge (because we do not have a larger version of them). We have concluded that these smaller images work fine for comparison purposes.  Later in the article, we show the World Forecasts.

JAMSTEC works only with three-month seasons: Summer JJA, Fall SON, and Winter DJF. Out of each three months, there is one where the months in the two forecasts align perfectly for the first time period. This is one of those months so for the first period we are comparing JJA for both JAMSTEC and NOAA. But we also have a separate June forecast from JAMSTEC. We have not usually had a single-month JAMSTEC forecast. I gather they make them but do not show them on their website. But they sent me two documents one containing the seasonal forecasts and one containing three monthly forecasts. So even though we are comparing seasonal forecasts starting with JJA, we are also able tonight to compare the June forecasts.

JAMSTEC is currently running a somewhat simplified version of their updated model. It is based on a 36 member ensemble, not 100, (apparently this version of the model was described in an article Doi et al. 2017, J. Climate). But they are using the new features which we had also been using in recent articles where we compared the two forecasts. One of the new features is a model of the temperature of the oceans by layers at various depths. This probably helps to incorporate the changing phases of ENSO into the forecast.

In addition to the value of comparing the JAMSTEC and NOAA forecasts, the JAMSTEC forecast by showing North America provides more context for the Alaska and CONUS Forecasts as the temperature and precipitation patterns cover North America, not just Alaska and CONUS.

Map Comparisons and our Comments

Temperature*

	NOAA Alaska Plus CONUS	JAMSTEC North America
June 2021
Summer JJA 2021
Fall SON 2021
Winter DJF 2021/2022

Precipitation*

	NOAA Alaska Plus CONUS	JAMSTEC North America
June 2021
Summer JJA 2021
Fall SON 2021
Winter DJF 2021/2022

* It is important to keep in mind that NOAA reports probabilities of being warmer or cooler than Climatology and JAMSTEC reports the degrees of temperature and millimeters of precipitation variation from Climatology (Normal). So they are not exactly comparable. Also please keep in mind that NOAA is now using a redefinition of Climatology which is the mean of the most recent three decades of weather namely 1991 to 2020. We do not believe that JAMSTEC has updated their definition of Climatology since the date of their forecast is May 1 which is prior to the time that NOAA did their update and there has been no announcement from JAMSTEC that they have updated their Climate Normals. This makes the comparisons more difficult. Where appropriate, we comment on this when discussing the comparison. 

JAMSTEC World Forecasts

This month our comments for Summer and Fall (Northern Hemisphere Seasons) are taken directly from the JAMSTEC discussion. We do not have a JAMSTEC discussion for the June forecast.

June 2021

Temperature

Precipitation

Summer which is JJA 2021

Temperature

Precipitation

Fall which is SON 2021

Precipitation

“

And Winter 2021/2022 which is DJF

Temperature

Precipitation

Here is the JAMSTEC Discussion

We provided the full JAMSTEC Discussion in Part I. We repeat it here.

ENSO forecast:

As predicted earlier, observation shows that the La Niña Modoki-like state decayed from boreal spring. The SINTEX-F predicts that a neutral state will persist in this year.

Indian Ocean forecast:

Observation shows that the western tropical Indian Ocean is warmer-than-normal. The SINTEX-F predicts that the present state will persist in boreal summer and autumn. However, there is a large uncertainty in the prediction.

Regional forecast:

On a seasonal scale, the SINTEX-F predicts that most part of the globe will experience a hotter-than-normal condition in boreal summer (austral winter) except for northern part of the South American Continent and some parts of Northern Europe. In boreal autumn (austral spring), the model still predicts most part of the globe will experience a warmer-than-normal condition, except for northern part of the South American Continent, some parts of northern Africa, and Ukraine.

As regards to the seasonally averaged rainfall in boreal summer (austral winter), a drier-than-normal condition is predicted for central/eastern U.S.A., southern part of the South American Continent, some parts of the Eurasian Continent, and Gabon.

In contrast, Mexico, northern part of the South American Continent, Philippines, some parts of Indonesia, some parts of West Africa, northern part of the Eurasian Continent, some parts of the Indochina Peninsula, eastern China, and the Korean Peninsula will experience a wetter-than-normal condition. In boreal autumn (austral spring), a wetter-than-normal condition is predicted for the South American Continent, central Africa, India, Philippines, and Indonesia. In contrast, most part of U.S.A., La Plata Basin, some parts of West Africa, and some parts of China will experience a drier-than-normal condition.

The model predicts most part of Japan will experience a hotter-than-normal condition in summer and autumn as a seasonal average. As regards to the seasonally averaged rainfall, most part of Japan will experience a slightly wetter-than-normal condition in summer and autumn as a seasonal average. Monthly prediction suggests an active rainy season (Baiu) in June.

D. Conclusion

As usual, there is a disagreement between NOAA and JAMSTEC. The differences are substantial this month but perhaps less substantial than usual.

It is difficult to relate the differences in the forecast to differences in assumptions on ENSO. But JAMSTEC tends to consider other factors that may not be considered by NOAA. On the other hand, the new versions of the JAMSTEC model are early in their usage and may not have been fully calibrated. I do not think I have gone into it in detail but when it comes to models we need to recognize that there are limitations and NOAA and JAMSTEC use very different approaches which I have summarized in the below table.

So it is kind of a pick your poison choice. But both agencies have great skill at employing approaches that have inherent limitations.

E. Additional Information

ENSO Phase

We showed some of this information in Part A on May 20, 2021. I am repeating it with some additions here.

Let us look at the NOAA recent ENSO Update. This happens every month on the second Thursday. I show this because it is the information that NOAA works from in producing the Four-Season Forecast.

Below is the probability analysis from mid-April and the probability analysis released on May 13, 2021

With respect to forecasts, this is interesting

It comes from the article written by Emily Becker and some may find that article very interesting. That forecast suggests a return of La Nina for next winter. This time of the year is not the best time to make predictions but the so-called Spring Prediction Barrier SPB applies more to predicting El Nino than predicting La Nina.

May 2021 ENSO update: bye for now, La Niña! Click to read

Here is the NOAA proprietary forecast which they rarely use.

 Here are the two JAMSTEC ENSO forecasts.

 When it differs from the Nino 3.4 forecast, the JAMSEC Modoki forecast becomes very important.

Sea Surface Temperature anomalies is probably the more important criteria for ENSO but the atmospheric response is also important and if the two do not agree, it is not possible to draw a conclusion that we are in an El Nino or La Nina state. After all, we are mostly interested in the atmosphere. Historically the Southern Oscillation Index has been what is relied on to measure the atmospheric response. Although it might not be the best index, the Australian SOI Index is what is generally most relied on. 

The Southern Oscillation Index or SOI being above 7 combined with the Nino 3.4 Index under -0.5 would confirm that the Atmosphere is in tune with the Sea Surface Temperatures in the Pacific along the Equator. At least temporarily the SOI Index is (barely) in neutral territory and is not confirming a La Nina but is sort of confirming ENSO Neutral. This is another graphic that we have not frozen.

Let us look at the part of the Pacific along the Equator from the surface down to 450 meters.

Below is the graphic above but also one issued last month. (I believe these images are five-day averages centered on the date shown.)

Prior Version	Updated Version

Here is the BOM Nino3.4 tracker.

Here is the BOM current forecast and I will let this graphic auto-update also. But it only updates every two weeks. But today is two weeks since May 8 and given the difference in time zones I am surprised that this graphic has not yet updated. After it updates I will freeze it so that this article will make more sense if read sometime in the future.

This is the IOD which is very important for the Indian Ocean. It is projected by JAMSTEC to be difficult to forecast through October.

Here is the BOM Forecast for the same Index.

F. Postscript.

The coordination between NOAA and IRI/CPC sucks to use a word that is fully descriptive of the situation.

NOAA issues their Seasonal Outlook on May 20 at the crack of dawn and IRI/CPC issued their second report of the month the day before on May 19. It is clear (by reading the NOAA Discussion) that NOAA did not utilize the second report from IRI/CPC and the methodology of the second report is different from the methodology of the first report of the month. So one wonders what gives? Is IRI/CPC trying to discredit NOAA or create confusion? This has been an ongoing problem and probably someone needs to be fired.

It is not that what they publish is not of interest. It is of great interest. And here it is:

And also

 We will know more on June 10, 2021 which is when we get the next formal NOAA ENSO Update. .