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Climate Outlook

ASIA April - September 2000

Issued: March 2000

The IRI has prepared this Climate Outlook for Asia for April - September 2000. Of relevance in the preparation of this Outlook has been the current La Niņa conditions (lower than average sea-surface temperatures (SSTs) in the central equatorial Pacific Ocean) that had been amplifying through the end of 1999. Thus, weakening La Niņa conditions are in effect for the first season of the forecast, April-May-June 2000, and a return to near-normal conditions is expected for the second forecast season, July-August-September 2000. The SSTs of the tropical Indian Ocean were assumed to remain near-normal. The forecast of tropical North Atlantic SSTs suggests a cooling trend through June 2000.

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 a rapid weakening of La Niņa conditions and a return to near-average conditions by the middle of 2000. The end of La Nina conditions is consistent with some, but not all, numerical and statistical forecasts of central and eastern Pacific SSTs.

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) Other sources of information include ( 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 the region. Thus, this product may differ from the official forecasts issued in those areas. The Climate Outlook for April - September 2000 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 concerning the evolution of SSTs. 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: April - June 2000 and July - September 2000. Maps are given showing 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 within the 1961-90 period (top number), the middle third of the years (middle number), and the driest third of the years (bottom number). 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 region I in April - June 2000 (Map B), there is a 25% probability that the precipitation will be in the wettest third of the years, a 30% chance it will be in the near-normal third of the years, and a 45% chance that the precipitation will be in the driest third of the years.

An additional precipitation 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. Climatologically, there is a 15% probability of being within the extremely wet category, and a 15% probability of being within the extremely dry category, leaving a 70% probability that the precipitation will not be extreme. The maps indicate areas of risk of extreme low or high precipitation totals. Three levels of increased risk are defined: slightly enhanced risk, enhanced risk, and greatly enhanced risk. For slightly enhanced risk, there is a 25-40% probability that precipitation will be within the indicated extreme, i.e. wet or dry. This represents an approximate doubling of the climatological risk. For enhanced risk, there is a 40-50% probability that precipitation will be within the indicated extreme. This represents an approximate tripling of the climatological risk. For greatly enhanced risk, the probability that precipitation will be within the indicated extreme exceeds 50%, i.e. the indicated extreme is the most likely outcome.

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 (Map A). 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.

April - June 2000:

PRECIPITATION

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

Region I) enhanced probabilities of below-normal precipitation over south-western Kazakhstan, and eastern Uzbekistan;

Region II) slightly enhanced probabilities of normal precipitation over central and southern Kazakhstan, Kygyzstan, Tajikistan, central and eastern Uzbekistan, eastern Turkmenistan, Afghanistan, and eastern Iran;

Region III) slightly enhanced probabilities of below-normal precipitation over Pakistan, and north-western India;

Region IV) slightly enhanced probabilities of below-normal precipitation over Taiwan and part of south-eastern China;

Region V) greatly enhanced probabilities of above-normal precipitation over much of Thailand and Cambodia, southern Myanmar, and the southernmost part of Vietnam;

Region VI) enhanced probabilities of above-normal precipitation over most of the Philippines (a slightly enhanced risk of extremely wet conditions is indicated);

Region VII) enhanced probabilities of below-normal precipitation over suthern Sumatra, southern Borneo, and most of the Celebes;

Region VIII) greatly enhanced probabilities of below-normal precipitation over Java;

Region IX) slightly enhanced probabilities of normal precipitation over Indonesian New Guinea;

Region X) enhanced probabilities of normal to above-normal precipitation over the Solomon Islands, and eastern and central Papua New Guinea;

Region XI) greatly enhanced probabilities of below-normal precipitation over Nauru and Kiribati.

TEMPERATURE

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

Region I) slightly enhanced probabilities of normal temperatures over western Mongolia;

Region II) enhanced probabilities of above-normal temperatures over southern Pakistan, and western India;

Region III) enhanced probabilities of above-normal temperatures over the Tibet region;

Region IV) greatly enhanced probabilities of above-normal temperatures over Sri Lanka, and the southernmost part of India;

Region V) greatly enhanced probabilities of above-normal temperatures over the south-eastern half of Myanmar, Thailand, Laos, Cambodia, and Vietnam;

Region VI) enhanced probabilities of above-normal temperatures over Taiwan and south-eastern China;

Region VII) greatly enhanced probabilities of above-normal temperatures over Japan and the Korean peninsula;

Region VIII) greatly enhanced probabilities of above-normal temperatures over an area including much of Indonesia, Papua New Guinea, the Solomon Islands, and extending northwards to the Northern Mariana Islands;

Region IX) greatly enhanced probabilities of above-normal temperatures over southern and central Philippines, eastern Malaysia, and northern-central Indonesia;

Region X) slightly enhanced probabilities of normal temperatures over southern Indonesia;

Region XI) greatly enhanced probabilities of below-normal temperatures over Nauru and Kiribati.

July - September 2000:

PRECIPITATION

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

Region X) slightly enhanced probabilities of above-normal precipitation over south-eastern Pakistan, and western and central India;

Region XI) slightly enhanced probabilities of below-normal precipitation over Sri Lanka and the far south-eastern part of India;

Region XII) enhanced probabilities of below-normal precipitation over western Malaysia, and part of western Indonesia;

Region XIII) slightly enhanced probabilities of normal precipitation over much of New Guinea and the Solomon Islands.

TEMPERATURE

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

Region XIII) slightly enhanced probabilities of below-normal temperatures over part of central and southern India;

Region XIV) enhanced probabilities of above-normal temperatures over Japan and the Korean peninsula;

Region XV) slightly enhanced probabilities of above-normal temperatures over much of extending from eastern China southwards to Sumatra, Malaysia, and the Philippines;

Region XVI) slightly enhanced probabilities of below-normal temperatures over the southern Indonesia.

OBSERVED CLIMATOLOGY DATA for Apr-May-Jun and Jul-Aug-Sep

CLIMATOLOGICAL AVERAGE: Temperature Precipitation

TERCILE THRESHOLDS (33%-ile & 67%-ile): Temperature Precipitation

EXTREME THRESHOLDS (15%-ile & 85 %-ile): Temperature Precipitation


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