Written by Sig Silber
We published the NOAA Long-Term Forecast Saturday Night. Here we compare the NOAA forecast for Alaska and CONUS with the JAMSTEC forecast. Also provided are the JAMSTEC World Forecasts. The two forecasts differ in minor ways with respect to temperature for Alaska and CONUS. But with respect to precipitation, the differences are drastic and could have serious consequences for the United States if JAMSTEC is correct.
Please share this article – Go to the very top of the page, right-hand side for social media buttons. Please feel free to send this article to anyone who you think might find it interesting and or useful.
Comparison of the NOAA and JAMSTEC Forecasts
Below (in what I call the “Summary”) is the comparison of the NOAA and JAMSTEC 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) and then JAMSTEC for North America (which includes Canada and Mexico). The NOAA forecasts can be clicked on to enlarge*. The JAMSTEC graphics in the Summary Table are not set up to be clicked on to enlarge (because we have no 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. Since we eliminated the Europe cut-outs from the World maps, the images in the summary matrix are larger.
* If for some reason that does not work, right-click and then click on view image and that should work. I checked it for all the NOAA images and four work by clicking on them and the other two will work if you right-click and then click view image. There are many mysteries to the Internet.
JAMSTEC works with three-month seasons as they view Summer as JJA (meteorological Summer) so from their perspective, it is time to focus on Summer JJA, Fall SON and Winter DJF. Out of each three months, there is one where the months in the two forecasts for the first time period align perfectly but this is not that month. The Summer maps for JAMSTEC are JJA. For NOAA we are also comparing their JJA forecast with the JAMSTEC forecast so that could be a bit confusing if you do not realize what is being compared but we think this is a more realistic comparison. The MJJ NOAA forecast is shown in Part I of this report which can be accessed here.
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.
Here is the Summary of our findings.
Temperature
| NOAA Alaska Plus CONUS | JAMSTEC North America | |
Summer JJA 2020 |  |  |
Fall SON 2020 |  |  |
Winter DJF 2020- 2021 |  | |
Precipitation
| NOAA Alaska Plus CONUS | JAMSTEC North America | |
Summer JJA 2020 |  |  |
Fall SON 2020 |  |  |
Winter DJF 2020 – 2021 |  |  |
We provided the full NOAA Discussion in Part I. The much shorter JAMSTEC Discussion was published on April 16, 2020, and we included it in Part I but we are repeating it here also.
ENSO forecast:
Observation shows a mixture of the El Niño Modoki-type and the canonical-type at present. The SINTEX-F predicts that the tropical Pacific will return to a neutral-state from summer.
Indian Ocean forecast:
Observation shows that the tropical Indian Ocean is warmer-than-normal at present. The model predicts that the present state will persist through the latter half of this year. However, there is a large uncertainty in the prediction (30% of the ensemble members actually predict a positive IOD event).
The strong negative Indian Ocean Subtropical Dipole still persists. The model predicts that it will disappear from summer.
Regional forecast:
On a seasonal scale, the SINTEX-F predicts that most part of the globe will experience a warmer-than-normal condition in boreal summer and autumn.
As regards to the seasonally averaged rainfall in boreal summer, a drier-than-normal condition is predicted for most part of U.S.A., northern part of the South American Continent, South Africa, southern part of West Africa, Indonesia, and southwestern China. In contrast, Mexico, most part of Southeast Asia, Philippines, India, and Sri Lanka will experience a wetter-than-normal condition. In boreal autumn, a wetter-than-normal condition is predicted for most part of Southeast Asia, India, Philippines, and Indonesia. In contrast, central U.S.A., Mexico, most part of the South American Continent, southern Africa, southern part of West Africa, and some parts of China will experience a drier-than-normal condition.
The model predicts most part of Japan will experience warmer and wetter-than-normal condition in summer as a seasonal average. In autumn, most part of Japan will be warmer and slightly wetter-than-normal.
JAMSTEC World Forecasts
This month our comments are taken directly from the JAMSTEC discussion.
Summer which is JJA
| Temperature |
 |
| Precipitation |
 |
Fall which is SON
 |
| Precipitation |
 |
And Winter which is DJF
| Temperature |
 |
| Precipitation |
 |
D. Conclusion
As usual, there is substantial disagreement between NOAA and JAMSTEC 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.
It may or may not be too early for NOAA to comment on the North American Monsoon but JAMSTEC does although it is difficult now to locate places down to the state level on the JAMSTEC maps. They used to show the state boundaries but no longer. Their forecast for the area that will be wet in JJA 2020 is very suggestive of good news for the western part of the Monsoon area but not for New Mexico or the Central Plains. NOAA is predicting an average Monsoon.
E. SINTEX Indices
I am showing these to illustrate how complex the SINTEX model is. They do not do a good job of labeling their indices.
