The IRI Experimental Forecast Division has prepared this Climate Outlook for Asia for October 1998 - March 1999. Of relevance in the preparation of this Outlook have been the continued evolution of cooler than average conditions in the eastern and central equatorial Pacific Ocean (La Niņa), and the persistence of warmer than average conditions in the western equatorial Pacific. The sea-surface temperatures of the central and western tropical Indian Ocean have been cooling from record high temperatures, and this trend is expected to continue. 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 during the forecast period.

METHODS -

This Outlook was prepared using the following procedures and information:

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 continued development of moderate La Niņa conditions, 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: CPC, the Queensland Department of Natural Resources, and ECMWF

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. This Outlook has been prepared using all information that was reasonably accessible. Inclusion of other climate information and guidance requires further arrangements. The IRI is engaged in establishing such collaborative arrangements with the goal of improving its capability to provide the best and most complete global climate guidance. The Climate Outlook for October 1998 - March 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 spread in coupled model predictions concerning the evolution of SSTs. This spread in predictions is a source of uncertainty in the Outlook provided here, which assumes that tropical Pacific SST's will continue to decline at a modest rate, resulting in moderate La Niņa conditions by the end of the year. Also, it is known that Indian Ocean SSTs may play some role in modulating precipitation changes over parts of Asia. Thus, the uncertainties in Indian Ocean SST values during the forecast period may lead to additional uncertainty over some parts of the region.

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: October - December 1998 and January - March 1999. Maps are given showing expected tercile probabilities of precipitation. The maps 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 marked "D" experience their dry season during the forecast period, typically receiving less than 15% of their annual precipitation total during the three months. Otherwise, for example, in the case of southern India in October - December 1998 (Map A), there is a 25% probability that the precipitation will be in the wettest third of the years, a 35% chance it will be in the near-normal third of the years, and a 40% 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.

October - December 1998:

PRECIPITATION

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

P.A) enhanced probabilities of below-normal precipitation in the former Soviet republics of Central Asia, Kazakhstan and western Siberia;

P.B) enhanced probabilities of above to near-normal precipitation over parts of central Siberia west to 120E;

P.C) enhanced probabilities of near-normal precipitation over eastern part of central Siberia and Sakhalin;

P.D) enhanced probabilities of above to near-normal precipitation over eastern Siberia;

P.E) enhanced probabilities of above to near-normal precipitation over Japan, with higher probabilities of above-normal precipitation over the northern part of the country (a slightly enhanced risk of extreme precipitation is indicated over this region);

P.F) greatly enhanced probabilities of above-normal precipitation in the Philippines, Indonesia excluding Sumatra, eastern Malaysia (a greatly enhanced risk of extremely wet conditions is indicated over the Philippines and central Indonesia);

P.G) slightly enhanced probabilities of below-normal precipitation over southern part of India and Ceylon.

TEMPERATURE

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

T.A) enhanced probabilities of above to near-normal temperatures over most of western and central Siberia, former Soviet republics of Central Asia, Kazakhstan, western half of Mongolia, and most parts of western and central China;

T.B) enhanced probabilities of warmer than normal conditions over eastern parts of Mongolia, north-eastern parts of China, Korea and Japan

T.C) enhanced probabilities of above-normal temperature over the Philippines, Malaysia and a part of south-east Asia;

T.D) enhanced probabilities of above-normal temperatures over central Vietnam, southern Laos, Northern Cambodia, central Thailand, and southern Burma;

T.E) enhanced probabilities of near-normal temperatures over northern Vietnam, northern and central Laos, northern Thailand, and eastern Burma.

T.F) slightly enhanced probabilities of above to near-normal temperature over India and Ceylon;

T.G) enhanced probabilities of normal conditions over Pakistan and Afghanistan.

January - March 1999:

PRECIPITATION

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

P.i) enhanced probabilities of above-normal precipitation over the Philippines and central Indonesia;

P.ii) slightly enhanced probabilities of above-normal precipitation over Malaysia and northern part of Sumatra;

P.iii) enhanced probabilities of below-normal precipitation over south-east China;

P.iv) slightly enhanced probabilities of above-normal precipitation over Afghanistan, Pakistan, former Soviet republics of Central Asia and southern parts of Kazakhstan.

TEMPERATURE

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

T.i) slightly enhanced probabilities of below to near-normal temperatures over western half of Siberia and northern parts of Kazakhstan;

T.ii) enhanced probabilities of above-normal temperatures over Japan, the Philippines, Malaysia, Borneo, southern half of India, most of Burma, Thailand, Vietnam, Laos and Cambodia.

Cutoffs and Max/Min extremes for OND and JAS.

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