Tropical rainfall and SST outlook: April to June 2009
During the March–May 2009 forecast period, a region of suppressed convection is likely in the southwest Pacific encompassing Tokelau, Tuvalu, and the Northern Cook Islands, with below average rainfall expected for those areas. Near to below average rainfall is expected for Eastern Kiribati and the Tuamotu Archipelago.
Enhanced convection is likely in the area around Papua New Guinea and Vanuatu, Fiji, Niue, and the Southern Cook Islands, with above average rainfall anticipated for the coming three month period. New Caledonia, the Austral Islands and Tonga are expected to receive near or above average rainfall. No clear precipitation guidance is offered for the Pitcairn, Samoa, Western Kiribati, Marquesas, the Society Islands, the Solomon Islands & Wallis and Futuna.
The prominent SST anomalies in the region that existed during the past few months are easing. Near or above average sea surface temperatures are forecast for eastern Papua New Guinea extending into the southwest Pacific, encompassing Vanuatu, Fiji, and New Caledonia, Wallis and Futuna, Tonga, Samoa, Niue, the Southern Cook Islands, the Society Islands, the Austral Islands, and Pitcairn Island. Near normal SSTs are forecast for the Marquesas and the Solomon Islands Average or below average SSTs are expected for Eastern Kiribati, Tuvalu, Western Kiribati, Tokelau, the Northern Cook Islands, and the Tuamotu Archipelago.
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 rainfall forecasts issued in April is 55%, 6% lower 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.