Tropical rainfall and SST outlook: December 2008 to February 2009
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.
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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.