Summary and interpretation for January to March 2011
Tropical situations including oceanic conditions in recent months
- In November 2010, the SST deviation from a sliding 30-year mean SST averaged over the NINO.3 region was -1.6°C for August. The five-month running-mean value of the NINO.3 SST deviations was -1.3°C for September. The Southern Oscillation Index for November was +1.5. In November, remarkably negative SST anomalies prevailed over most of the equatorial Pacific, except near Indonesia.
- Subsurface temperature anomalies were positive in the western equatorial Pacific, and were remarkably negative in the central and the eastern parts. In the equatorial Pacific, convective activities near the date line were below normal. Easterly wind anomalies in the lower troposphere prevailed in the western and the central equatorial Pacific. The oceanic and atmospheric features mentioned above reflect La Niña conditions.
- In the equatorial Pacific, persistent easterly anomalies in the lower troposphere maintained the negative subsurface temperature anomalies in the central and the eastern parts. The negative subsurface temperature anomalies will, in turn, keep SSTs below normal.
- The JMA's El Niño prediction model predicts that the NINO.3 SST will be below normal during boreal winter, and will gradually become near normal during boreal spring.
- Considering all the above, La Niña conditions are likely to decay during boreal winter or spring.
- It is likely that the SST in the NINO.WEST will be above normal during boreal winter, and will gradually become near normal during boreal spring.
Interpretation of ensemble prediction products for January to March 2011
- The NINO.3 SST deviation is predicted to be below normal and the La Niña conditions will continue almost through the predicted period.
- In association with the SST anomaly pattern, the predicted ensemble averaged atmospheric circulation anomaly pattern by the model is also similar to that of observed La Niña events in the tropics and the sub-tropics especially in January as stated below.
- In the lower tropospheric (850-hPa) stream function field, a cyclonic circulation anomaly is predicted around Japan. It suggests that cold air is likely to flow into Japan.
- In the upper tropospheric (200-hPa) stream function field, an anti-cyclonic circulation anomaly is predicted to the south of China, followed by a cyclonic one centered west of Japan in January. The anomaly pattern seems to form a stationary Rossby wave train which is forced by the divergent flow associated with the precipitation anomalies, and propagates along the Asia jet stream. The predicted wave train causes the large-scale southward shift of the jet over Japan, which tends to bring cold weather around Western Japan and Okinawa/Amami in January. On the other hand, cyclonic circulation anomalies are not predicted around Japan in February and March.
- Zonally-averaged tropospheric air temperature in the middle latitudes of the Northern Hemisphere is predicted to be higher than normal. It indicates that warm air is expected to be predominant in the mid-latitudes including Japan.
- In the mid- and high-latitudes, the neutral phase of the Arctic Oscillation (AO) is predicted. The positive (negative) phase of AO tends to cause weak (strong) winter monsoon, and above-normal (below-normal) temperature in Northern Japan. However, the spread among each ensemble member is large and hindcasting suggests that the model does not have a sufficient level of skill to predict AO accurately, so the model results should be interpreted with caution.
Summary of the outlooks for Japan (January to March 2011)
- Three-month mean temperatures are expected to be above normal with 50% probability in Northern Japan and both near-normal and above normal with 40% probabilities in Eastern Japan. In January, monthly mean temperature is expected to be both near-normal and below normal with 40% probabilities in Western Japan and Okinawa/Amami.
- Three-month total precipitation is expected to be both near-normal and below normal with 40% probabilities on the Sea of Japan side of Northern Japan.
| Forecast Period | 3 months | 1st month | 2nd month | 3rd month |  |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jan-Mar | Jan | Feb | Mar | ||||||||||
| category | – | 0 | + | – | 0 | + | – | 0 | + | – | 0 | + | |
| Northern Japan | 20 | 30 | 50 | 20 | 40 | 40 | 20 | 40 | 40 | 20 | 30 | 50 | |
| Eastern Japan | 20 | 40 | 40 | 30 | 40 | 30 | 20 | 40 | 40 | 20 | 30 | 50 | |
| Western Japan | 30 | 40 | 30 | 40 | 40 | 20 | 30 | 30 | 40 | 20 | 40 | 40 | |
| Okinawa and Amami | 30 | 40 | 30 | 40 | 40 | 20 | 30 | 30 | 40 | 20 | 40 | 40 | |
| Forecast Period | 3 months | 1st month | 2nd month | 3rd month |  |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jan-Mar | Jan | Feb | Mar | |||||||||||
| category | – | 0 | + | – | 0 | + | – | 0 | + | – | 0 | + | ||
| Northern Japan | Sea of Japan side | 40 | 40 | 20 | 40 | 30 | 30 | 40 | 30 | 30 | 40 | 40 | 20 | |
| Pacific side | 30 | 40 | 30 | 30 | 30 | 40 | 30 | 40 | 30 | 30 | 40 | 30 | ||
| Eastern Japan | Sea of Japan side | 30 | 40 | 30 | 30 | 40 | 30 | 30 | 40 | 30 | 30 | 40 | 30 | |
| Pacific side | 30 | 40 | 30 | 30 | 40 | 30 | 30 | 40 | 30 | 30 | 40 | 30 | ||
| Western Japan | Sea of Japan side | 30 | 40 | 30 | 30 | 30 | 40 | 30 | 40 | 30 | 30 | 40 | 30 | |
| Pacific side | 30 | 40 | 30 | 40 | 30 | 30 | 30 | 40 | 30 | 30 | 40 | 30 | ||
| Okinawa and Amami | 30 | 40 | 30 | 40 | 30 | 30 | 30 | 40 | 30 | 30 | 40 | 30 | ||
| Forecast Period | 3 months |  |
|||
|---|---|---|---|---|---|
| Jan-Mar | |||||
| category | – | 0 | + | ||
| Northern Japan | Sea of Japan side | 50 | 30 | 20 | |
| Eastern Japan | Sea of Japan side | 30 | 40 | 30 | |
| Western Japan | Sea of Japan side | 30 | 40 | 30 | |
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