Tropical rainfall and SST outlook: March to May 2009
During the March–May 2009 forecast period, a region of suppressed convection is likely to encompass the central and eastern Southwest Pacific, extending to the southeast from Tuvalu to the Northern Cook Islands, including Tokelau, where below normal rainfall is expected. Near–to–below normal rainfall is expected for Samoa, Eastern Kiribati, and Western Kiribati.
Enhanced convection is expected to extend southeast from, Papua New Guinea, and include New Caledonia, Vanuatu, Tonga, the Southern Cook Islands and the Austral Islands, where above normal rainfall is forecast. Near or above normal rainfall is forecast for the Fiji and Niue. Normal rainfall is anticipated for the Marquesas, Pitcairn Island, and also the Society Islands. No clear precipitation guidance is offered for the Solomon Islands, Tuamotu, or Wallis & Futuna for the three-month forecast period.
SSTs are expected to be above normal around eastern Papua New Guinea, and surrounding Vanuatu, Fiji and New Caledonia. Near normal or above normal SSTs are also expected for Niue, Tonga, Wallis & Futuna, the Southern Cook Islands, the Society Islands, Austral Islands, and Pitcairn Island. Near normal or below normal SSTs are forecast for the Tuamotu archipelago, the Northern Cook Islands, Tuvalu, Tokelau, and Eastern & Western Kiribati.
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 March is 63%, 1% 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.