Written by Sig Silber
We published the NOAA Long-Term Forecast Part I on August 19, 2021. Tonight we compare the NOAA forecast for Alaska and CONUS with the JAMSTEC forecast. 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. They are worth looking at. 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 September forecasts this time. Surprisingly the amount of disagreement is pretty significant.
Coping With Weak Signals with Respect to ENSO.
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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 September and then three season defined 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: Right now that is Fall: SON, Winter: DJF and 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. This is a month where the two forecasts line up perfectly. But in addition, all of a sudden, JAMSTEC has changed the process so I have forecast maps from JAMSTEC for September, October, and November. I think this is an improvement. So I am now able to match up the NOAA and JAMSTEC maps exactly plus also compare the single month of September.
It is important to remember that the NOAA forecast is dated August 19 so it was probably prepared on August 17 or 18 and the JAMSTEC forecast is dated August 1. That is important when comparing assumptions when things are changing rapidly. |
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 | |
September 2021 | ||
Fall SON 2021 | ||
Winter DJF 2021-2022 | ||
Spring MAM 2022 |
Precipitation*
NOAA Alaska Plus CONUS | JAMSTEC North America | |
September 2021 | ||
Fall SON 2021
| ||
Winter DJF 2021-2022 | ||
Spring MAM 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 Fall and Winter (Northern Hemisphere Seasons) are taken directly from the JAMSTEC discussion.
September 2021
Temperature |
Precipitation |
Fall which is SON
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 autumn (austral spring) except for northern parts of the South American Continent”..”As regards to the seasonally averaged rainfall in boreal autumn (austral spring), a drier-than-normal condition is predicted for California, southern parts of the South American Continent, most parts of southern Africa, some parts of West Africa, some parts of Europe, some parts of Indochina, and most parts of China. In contrast, most parts of Alaska, the western coastal area of Canada, Central America, northern parts of the South American Continent, some parts of Central Africa, India, Philippines, and Indonesia will experience a wetter-than-normal condition. Some parts of West Africa will also experience a wetter-than-normal condition due to the evolving Atlantic Niño. Extremely wetter-than-normal conditions in Indonesia will be mostly due to the evolving negative Indian Ocean Dipole.”
Winter which is DJF 2021-2022
Precipitation |
“ |
Spring which is MAM 2022
Precipitation |
“ |
I do not usually present this and I am doing it in a way that you have three seasons shown in one image rather than three separate (and thus larger) images but I think you can see some things.
Here is the JAMSTEC Discussion
ENSO forecast:
Observation shows that the tropical Pacific is in a neutral state. The SINTEX-F predicts that a weak La Niña Modoki-like state will appear in boreal autumn.
Indian Ocean forecast:
As predicted earlier, observation shows occurrence of a negative Indian Ocean Dipole. The SINTEX-F ensemble mean predicts that the Indian Ocean will return to a neutral state in boreal autumn. However, there is a large uncertainty in the predictions, and the SINTEX-F2-3DVAR, which predicted most recent IOD events, predicts that a weakly negative Indian Ocean Dipole will persist in boreal 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 autumn (austral spring) except for northern parts of the South American Continent. In boreal winter (austral summer), the model still predicts most parts of the globe will experience a warmer-than-normal condition, except for northern parts of the South American Continent and some parts of Europe.
As regards to the seasonally averaged rainfall in boreal autumn (austral spring), a drier-than-normal condition is predicted for California, southern parts of the South American Continent, most parts of southern Africa, some parts of West Africa, some parts of Europe, some parts of Indochina, and most parts of China. In contrast, most parts of Alaska, the western coastal area of Canada, Central America, northern parts of the South American Continent, some parts of Central Africa, India, Philippines, and Indonesia will experience a wetter-than-normal condition. Some parts of West Africa will also experience a wetter-than-normal condition due to the evolving Atlantic Niño. Extremely wetter-than-normal conditions in Indonesia will be mostly due to the evolving negative Indian Ocean Dipole. In boreal winter (austral summer), a wetter-than-normal condition is predicted for Alaska, northern parts of the South American Continent, Philippines, and Indonesia. In contrast, most parts of Australia, some parts of southern Africa, and some parts of Europe will experience a drier-than-normal condition.
The model predicts most parts of Japan will experience a warmer-than-normal condition in autumn and winter as a seasonal average. As regards to the seasonally averaged rainfall, the model predicts almost neutral conditions over most parts of Japan in autumn. In winter, Okinawa and southern parts of Japan will experience a drier-than-normal condition
C2. ENSO Assumptions
Now 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. We have covered some of this when we reported on the IRI/CPC analysis on July 8, 2021. I have added the JAMSTEC assumptions and also the Australian Bureau of Meteorology Assumptions.
So it is useful to look at the model runs of another weather agency the Australian Bureau of Meteorology
ENSO UPDATE (what we reported with our August 19 Part I Article with some updates)
But then August 19 comes around and CPC/IRI decides to publish again.
Below is a NOAA graphic that is not part of the release of information by NOAA when they discuss ENSO. It is a cross-section of the Equatorial Pacific right along the Equator. What counts is the surface temperature and this only shows the Equator and the actual calculation is based on the temperature anomaly from 170W to 120W but including 5 degrees north and south of the Equator. I have a different graphic that shows that but just the surface and this one is probably more accurate for the area shown. The water is anomalously cold east of 170W. So that look like La Nina to me. We will get the interpretation from NOAA on September 9, 2021 so that is quite a while from now.
But to take a closer look I snip the top part which shows the temperature anomalies and compare it to what it looked like just five days ago.
August 11, 2021 | August 16, 2021 |
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.
Here is the BOM (Australia Bureau of Meteorology) Nino3.4 tracker.
Here is their current forecast.
D. Conclusion
As usual, there is a disagreement between NOAA and JAMSTEC. The differences are substantial with respect to both temperature and 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.