Written by Sig Silber
We published the NOAA Long-Term Forecast Part I Saturday Night. Here we compare the NOAA forecast for Alaska and CONUS with the JAMSTEC forecast. Also provided are the JAMSTEC World Forecasts. For Alaska and CONUS there is a lot of disagreement – more relative to precipitation than temperature. It is easier to see the disagreements by comparing the maps but we have attempted to create a summary table. As we indicated in our Part I Report on Saturday Night, our level of confidence drops off rapidly after the Summer Season due to lack of confidence in the ability to forecast the ENSO phase into late Fall and Winter. That is not a criticism of either agency.
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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.
JAMSTEC works 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 for the first time period align perfectly and this is that month so that simplifies things. .
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 May 14, 2020, and we included it in Part I but we are repeating it here also.
May 14, 2020 Prediction issued on May 1, 2020
ENSO forecast:
Observation shows that almost all of the tropical Pacific Ocean is warmer-than-normal 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 the evolution of a moderately negative Indian Ocean Dipole from boreal summer.
The strong negative Indian Ocean Subtropical Dipole still persists. The model predicts that it will disappear from austral winter.
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 central part of U.S.A., California, northern part of the South American Continent, and West Africa. In contrast, most part of Southeast Asia, Philippines, Indonesia, India, eastern China, and the Korean Peninsula will experience a wetter-than-normal condition. In boreal autumn, a wetter-than-normal condition is predicted for northwestern coastal area of Canada, most part of the South American Continent, Philippines, and Indonesia. In contrast, northwestern part of southern Africa, southern part of West Africa, India, some parts of the Southeast Asia, southern 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 and autumn as a seasonal average.
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.
E. SINTEX Indices
I am showing these to illustrate how complex the SINTEX model is. They do not do a good job of labeling all of their indices. I am not sure I have the expertise and I am sure I do not have the time to relate the forecast of the indices to the weather forecast maps and there is no guarantee that the forecasts of the indices are correct. But it does provide some insight into what the JAMSTEC forecast is what it is.
