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Three-month outlook

Tropical rainfall and SST outlook: December 2008 to February 2009

Rainfall outlook map for December 2008 to February 2009. (Click for enlargement)

Sea surface temperature outlook map for December 2008 to February 2009. (Click for enlargement)

During the December 2008–February 2009 forecast period, a region of suppressed convection is likely to encompass the central and eastern Southwest Pacific, in a region extending from Western Kiribati to the Marquesas Islands, including Tuvalu, Tokelau, Wallis & Futuna, Samoa, the Northern Cook Islands, and the Tuamotu archipelago. Below normal rainfall is expected for those countries. Near–to–below normal rainfall is expected for the Society Islands, Pitcairn Island, and Eastern Kiribati.

Enhanced convection is expected to extend southeast from Papua New Guinea, encompassing the Solomon Islands, Vanuatu, New Caledonia, Tonga, and Niue with above average rainfall. Near–to–above average rainfall is forecast for Fiji, Wallis & Futuna, the Southern Cook Islands, and the Austral Islands for the next three-month period.

SSTs are expected to be near–to–above normal in a band extending from near Papua New Guinea, southeast to Fiji, including Vanuatu, New Caledonia, the Solomon Islands, Niue, the Southern Cook Islands, the Austral Islands, and Pitcairn Island. Normal to below normal SSTs are forecast for the northeastern sector of French Polynesia, including the Tuamotu archipelago and the Society Islands, Tuvalu, Tokelau, and Eastern Kiribati. Western Kiribati is projected for normal SSTs during this time.

The confidence in the forecast model skill for this seasonal rainfall outlook is moderately high for most Pacific Island countries. In the past, the average region-wide hit rate for forecasts issued in December is 67%, 6% higher than the long-term average for all months combined. The SST forecast confidence is moderate–to–high for this period.

Island group Rainfall outlook Outlook confidence
Papua New Guinea 20:35:45 (Above) Moderate - high
New Caledonia 20:35:45 (Above) High
Niue 20:35:45 (Above) High
Tonga 20:35:45 (Above) High
Vanuatu 20:35:45 (Above) High
Solomon Islands 20:35:45 (Above) Moderate - high
Fiji 20:40:40 (Near or above) Moderate - high
Austral Islands 20:40:40 (Near or above) High
Cook Islands (Southern) 20:40:40 (Near or above) High
Wallis & Futuna 25:35:40 (Near or above) Moderate
Kiribati (Eastern) 40:40:20 (Near or below) Moderate - high
Society Islands 45:35:20 (Near or below) Moderate
Marquesas Islands 45:35:20 (Below) Moderate
Pitcairn Islands 45:35:20 (Below) Moderate - high
Cook Islands (Northern) 40:35:25 (Below) Moderate - high
Tuamotu Islands 50:30:20 (Below) Moderate - high
Samoa 50:30:20 (Below) Moderate
Kiribati (Western) 50:30:20 (Below) Moderate - high
Tokelau 50:30:20 (Below) High
Tuvalu 50:30:20 (Below) Moderate - high
Island group SST Outlook Outlook confidence
Fiji 25:35:40 (Near or above) Moderate - high
New Caledonia 25:35:40 (Near or above) Moderate - high
Papua New Guinea 25:35:40 (Near or above) Moderate - high
Vanuatu 25:35:40 (Near or above) Moderate - high
Cook Islands (Southern) 25:35:40 (Near or above) Moderate - high
Austral Islands 25:40:35 (Near or above) Moderate - high
Pitcairn Islands 25:40:35 (Near or above) Moderate - high
Samoa 25:40:35 (Near or above) Moderate - high
Wallis & Futuna 25:40:35 (Near or above) Moderate - high
Niue 25:40:35 (Near or above) Moderate - high
Solomon Islands 25:40:35 (Near or above) Moderate - high
Tonga 25:40:35 (Near or above) Moderate - high
Society Islands 25:40:35 (Near or above) Moderate - high
Kiribati (Western) 30:40:30 (Near normal) Moderate
Tuamotu Islands 30:40:30 (Near or below) Moderate - high
Cook Islands (Northern) 35:40:25 (Near or below) Moderate - high
Marquesas Islands 35:40:25 (Near or below) Moderate
Tokelau 35:40:25 (Near or below) Moderate - high
Tuvalu 35:40:25 (Near or below) Moderate - high
Kiribati (Eastern) 40:40:20 (Near or below) Moderate

NOTE: Rainfall estimates for Pacific Islands for the next three months are given in the table. The tercile probabilities (e.g., 20:30:50) are derived from the interpretation of several global climate models. They correspond to the odds of the observed rainfall being in the lowest (driest) one third of the rainfall distribution, the middle one third, or the highest (wettest) one third of the distribution. On the long-term average, rainfall is equally likely (33% chance) in any tercile.