The IRI Experimental Forecast Division has prepared this Climate Outlook for Asia for January - June 1999. Of relevance in the preparation of this Outlook have been the continuation of cooler than average sea-surface temperatures (SSTs) in the eastern and central equatorial Pacific Ocean (La Niña), and the persistence of warmer than average conditions in the western Pacific. The SSTs of the central tropical Indian Ocean have cooled from record high temperatures in 1998. The SSTs there are currently below average, and negative anomalies are expected to persist. It has been assumed that the northern and tropical Atlantic Ocean will remain warmer than normal, and that sea-surface temperatures in the South Atlantic will increase slightly during the forecast period.

METHODS -

A) Coupled ocean-atmosphere model predictions of tropical Pacific SST covering the forecast period. Particularly heavy weighting has been given to predictions from the coupled model operated by the NOAA National Centers for Environmental Prediction, Climate Modeling Branch. This model suggests the continuation of moderate La Niña conditions, slowly decaying by the end of the forecast period, with the persistence of positive sea-surface temperature anomalies in the region of Indonesia. This sea-surface temperature forecast is consistent with most other numerical and statistical forecasts.

B) Forecasts of the tropical Indian and Atlantic oceans using statistical models developed by the IRI and CPTEC respectively.

C) Global atmospheric circulation model (GCM) predictions of the atmospheric response to the present and predicted sea-surface temperature patterns.

D) Statistical analyses of the observed climate over Asia.

E) Other sources of information include (ECMWF ; UKMO).

The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in Asia. Thus, this product may differ from the official forecasts issued in those areas. The Climate Outlook for January - June 1999 is dependent on the quality of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is some uncertainty between coupled model predictions concerning the detailed evolution of SSTs. This spread in global SST predictions is a source of uncertainty in the Outlook provided here.

It is stressed that the current status of seasonal-to-interannual climate forecasting allows prediction of spatial and temporal averages, and does not fully account for all factors that influence regional and national climate variability. This Outlook is relevant only to seasonal time scales and relatively large areas; local variations should be expected. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.

OUTLOOK -

This Outlook covers two seasons: January - March 1999 and April - June 1999. Maps are given showing expected tercile probabilities of precipitation and temperature. The maps for precipitation indicate the probabilities that the seasonal precipitation will fall into the wettest third of the years (top number), the middle third of the years (middle number), or the driest third of the years (bottom number). An additional map is provided for the first season indicating probabilities for extreme precipitation anomalies. Extremes are defined as anomalies that fall within the top and bottom 15th percentile of the observed records. Maps of temperature show expected probabilities that the seasonal temperatures will fall into the warmest third of the years, the middle third of the years, or the coldest third of the years. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category.

Areas that are marked by "D" represent regions experiencing their dry season (less than 15% of annual precipitation) and for which less than 5cm of precipitation typically occurs over the season. Otherwise, for example, in the case of the Philippines in January - March 1999 (Map A), there is a 65% probability that the precipitation will be in the wettest third of the years, a 25% chance it will be in the near-normal third of the years, and a 10% chance that the precipitation will be in the driest third of the years. The numbers for each region on the temperature maps indicate the probabilities of temperatures to fall in each of the three categories, above-, near-, and below-normal. Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.

January - March 1999:

PRECIPITATION

The following regions of enhanced probabilities of precipitation anomalies are indicated:

P.A) slightly enhanced probabilities of below-normal precipitation over northern Kazakhstan / southern Siberia, Pakistan, and Afghanistan;

P.B) slightly enhanced probabilities of below-normal precipitation over south-eastern China;

P.C) enhanced probabilities of near-normal precipitation over central Indonesia and eastern Malaysia (over Borneo and Celebes);

P.D) enhanced probabilities of near-normal to above-normal precipitation over northern Sumatra and the Malay Peninsula;

P.E) slightly enhanced probabilities of above normal precipitation over Korea, the Japanese islands of Honshu and Kyushu, and over much of south-east Asia;

P.F) greatly enhanced probabilities of above-normal precipitation over the Philippines (there is an indication of an enhanced risk of extremely wet conditions).

TEMPERATURE

The following regions of enhanced probabilities of temperature anomalies are indicated:

T.A) enhanced probabilities of above-normal temperatures over much of eastern Asia, west of about 70E, covering the northern half of China and the southern half of Siberia, and a slight enhancement of probability of above-normal temperatures over the rest of Siberia and northern Russia;

T.B) enhanced probabilities of near-normal temperatures over India and Sri Lanka;

T.C) enhanced probabilities of near-normal temperatures over the Marshall Islands;

T.D) slightly enhanced probabilities of above-normal temperatures over much of south-east Asia, from Burma to Vietnam, and including Malaysia, northern Indonesia, and the Philippines.

April - June 1999:

PRECIPITATION

The following regions of enhanced probabilities of precipitation anomalies are indicated:

P.i) slightly enhanced probabilities of below-normal precipitation over the former Soviet republics of Central Asia, extending over Afghanistan and into western China;

P.ii) slightly enhanced probabilities of below-normal precipitation over south-eastern India and Sri Lanka;

P.iii) slightly enhanced probabilities of above-normal precipitation over much of south-east Asia including Thailand,

Laos, Cambodia, Vietnam, most of Malaysia, and the Philippines;

TEMPERATURE

The following regions of enhanced probabilities of temperature anomalies are indicated:

T.i) slightly enhanced probabilities of above-normal temperatures over north-western China and the Japanese islands of Honshu and Kyushu;

T.ii) enhanced probabilities of above-normal temperatures for the Philippines, western Borneo.

Cutoffs and Max/Min extremes for JFM and AMJ.

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