Three-month outlook

Tropical rainfall and SST outlook: January to March 2009

Rainfall outlook map for January to March 2009. (Click for enlargement)

Sea surface temperature outlook map for January to March 2009. (Click for enlargement)

During the January–March 2009 forecast period, a region of suppressed convection is likely to encompass the central and eastern Southwest Pacific, extending from Western Kiribati to Eastern Kiribati, including Tuvalu, Tokelau, the Northern Cook Islands, and the Tuamotu archipelago. Below normal rainfall is expected. Near–to–below normal rainfall is expected for Samoa.

Enhanced convection is expected to extend southeast from, Vanuatu and New Caledonia, to the Austral Islands, includingTonga, Fiji, Wallis & Futuna, and Niue, with above averagerainfall projected. No precipitation guidance is offered for Pitcairn Island, Papua New Guinea, the Solomon Islands, the Marquesas, or the Society Islands for the three-month forecast period.

SSTs are expected to be above normal in a band extending from near Papua New Guinea, southeast to Vanuatu and New Caledonia, including the Solomon Islands, and above normal SSTs are also expected for Niue and Tonga. Near–to–above normal SSTs are forecast for Fiji, the Southern Cook Islands, the Society Islands, the Austral Islands, and Pitcairn Island. 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 to have normal–to–below normal SSTs.

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 January is 56%, 5% lower than the long-term average for all months combined. The SST forecast confidence is moderate–to–high for this period.

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.