Written by Sig Silber
Edited at 4:40 pm EDT June 21, 2021 to correct one spelling error and add a little more explanation at the very end of the article.
We published the NOAA Long-Term Forecast Part I on June 17, 2021. Tonight we compare the NOAA forecast for Alaska and CONUS with the JAMSTEC forecast. For comparison we show the maps side by side in a table with a summary. Obviously, the farther out you look, the less confidence you have in the forecasts and thus also 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. 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 July 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
C1. The Comparison
Below is the comparison of the NOAA and JAMSTEC temperature and precipitation forecast maps for the month of July and then three time-periods. In the Summary Table we show the NOAA forecast for Alaska and CONUS (the contiguous mid-latitude U.S) and right next to it the JAMSTEC forecast 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 normally works only with three-month seasons: Summer JJA, Fall SON, and Winter DJF (and when.appropriate Spring MAM). Out of each three months, there is normally just one where the months in the two forecasts align perfectly for the first time period. But all of a sudden they have changed the process so I have forecast maps from JAMSTEC for JAS and SON in addition to Winter DJF. I think this is an improvement even though there is some overlap between the JAS and SON maps. But I am now able to match up the NOAA and JAMSTEC maps exactly. And we also have a separate July forecast from JAMSTEC. We have not usually had single-month JAMSTEC forecasts. I gather they make them but do not show them on their website. But they sent me a document with the seasonal forecasts and also three monthly forecasts: July, August and September. So in addition to comparing seasonal forecasts starting with JJA, we are tonight also able to compare the July forecasts.
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 | |
July 2021 |  |  |
Late Summer JAS 2021 |  |  |
Fall SON 2021 |  |  |
Winter DJF 2021/2022 |  |  |
Precipitation*
| NOAA Alaska Plus CONUS | JAMSTEC North America | |
July 2021 |  |  |
| Late Summer JAS 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, They may have but there has been no announcement from JAMSTEC that they have updated their Climate Normals. This makes the comparisons a bit more difficult.
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 July forecast.
July 2021
| Temperature |
 |
| Precipitation |
 |
Late Summer which is JAS 2021
| Temperature |
 |
| Precipitation |
 |
JAMSTEC says: “On a seasonal scale, the SINTEX-F predicts that most parts of the globe will experience a hotter-than-normal condition in boreal summer (austral winter) except for northern parts of the South American Continent, some parts of India, Indonesia, and northwestern Russia.”…”As regards to the seasonally averaged rainfall in boreal summer (austral winter), a drier-than-normal condition is predicted for central parts of the North American Continent, southern parts of the South American Continent, most parts of the Eurasian Continent, southern part of the Sahara Desert. In contrast, southern Alaska, the western coastal area of Canada, southeastern U.S.A., northern parts of the South American Continent, Philippines, Indonesia, some parts of West Africa, some parts of Central Africa, northern parts of the Eurasian Continent, India, some parts of the Indochina Peninsula, eastern China, and the Korean Peninsula will experience a wetter-than-normal condition.”…”The model predicts most parts of Japan will experience a hotter-than-normal condition in summer as a seasonal average. As regards to the seasonally averaged rainfall, Hokkaido will experience a slightly wetter-than-normal condition in summer. Monthly prediction suggests a wetter-than-normal condition in August.”
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 tropical Pacific returned to a neutral state. The SINTEX-F predicts that a weak La Niña Modoki-like state will appear in boreal autumn.
Indian Ocean forecast:
Observation shows that the central/eastern tropical Indian Ocean is warmer-than-normal. The SINTEX-F predicts that a negative Indian Ocean Dipole will occur in boreal summer and autumn.
Regional forecast:
On a seasonal scale, the SINTEX-F predicts that most parts of the globe will experience a hotter-than-normal condition in boreal summer (austral winter) except for northern parts of the South American Continent, some parts of India, Indonesia, and northwestern Russia. In boreal autumn (austral spring), the model still predicts most parts of the globe will experience a warmer-than-normal condition, except for Alaska, northern parts of the South American Continent, some parts of Indonesia, India, Indochina, eastern China, Saudi Arabia, and the Middle East.
As regards to the seasonally averaged rainfall in boreal summer (austral winter), a drier-than-normal condition is predicted for central parts of the North American Continent, southern parts of the South American Continent, most parts of the Eurasian Continent, southern part of the Sahara Desert. In contrast, southern Alaska, the western coastal area of Canada, southeastern U.S.A., northern parts of the South American Continent, Philippines, Indonesia, some parts of West Africa, some parts of Central Africa, northern parts of the Eurasian Continent, India, 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 western coastal area of Canada, most parts of the South American Continent, eastern Australia, eastern parts of southern Africa, northern parts of Europe, northern parts of the Eurasian Continent, India, Philippines, and Indonesia. In contrast, most parts of U.S.A., La Plata Basin, western parts of southern Africa, some parts of West Africa, southern parts of Europe, and eastern China will experience a drier-than-normal condition. Extremely wetter-than-normal conditions in Indonesia will be mostly due to the evolving negative Indian Ocean Dipole.
The model predicts most parts of Japan will experience a hotter-than-normal condition in summer and autumn as a seasonal average. As regards to the seasonally averaged rainfall, Hokkaido will experience a slightly wetter-than-normal condition in summer. Monthly prediction suggests a wetter-than-normal condition in August.
ENSO Assumptions
First I present what we reported on after the NOAA Update on June 10, 2019 plus the JAMSTEC assumptions and a couple of forecasts from the Australian Bureau of Meteorology (B0M). Then I report some recent information that as usual confuses the picture a bit.
C2. Assumptions that we believe impacted the NOAA and JAMSTEC forecasts.
We have covered some of this when we reported on the IRI/CPC analysis on June 10, 2021. I show this because it is the information that NOAA works from in producing the Four-Season Forecast.
ENSO Update
Now we have the JAMSTEC models.
First the standard Nino 3.4 model
Then the Modoki Model
The Southern Oscillation Index or SOI being above 7 confirms that the Atmosphere is in tune with the Sea Surface Temperatures in the Pacific along the Equator. At least temporarily the SOI Index is in neutral territory. This is another graphic that we have not frozen.
Let’s take a closer look at the Equator in the Pacific Ocean
Below is the graphic above but also one issued a month earlier. (I believe these images are five-day averages centered on the date shown.)
| Prior Version | Updated Version |
 |
|
Here is the BOM (Australia Bureau of Meteorology) Nino3.4 tracker.
Here is the BOM current forecast.
Indian Ocean Dipole
JAMSTEC Forecast
BOM Forecast
C.3 Some recent information from IRI/CPC which seems to delight in confusing the recently released NOAA Seasonal Outlook.
And they also released this graphic:
D. Conclusion
As usual, there is a disagreement between NOAA and JAMSTEC. The differences are substantial especially with respect to precipitation.
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.
| Shorter Term | Intermediate-Term | |
| NOAA | Deterministic | Statistical |
| JAMSTEC | Deterministic | Deterministic (may also use statistical methods) |
| Assessment | Generally Considered to be reliable for 14 to 28 days | Errors build up in deterministic models and statistical models generally have insufficient historical data to be reliable |
So it is kind of a pick your poison choice. But both agencies have great skill at employing approaches that have inherent limitations. The following is an addition to what I published last night. Statistical methods may not handle Modokis very well. There are not that many ENSO events to begin with. If you subdivide them into more and more groups, the sample size gets smaller and thus the confidence interval gets wider. But JAMSTEC is not able to escape the same problem by usine deterministic methods since the problem will show up with attempts to calibrate the model.
