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Tropical rainfall and SST outlook: February to April 2012

A La Nina pattern continues to be evident in the ensemble of global climate forecasts.

Suppressed convection is expected in the southwest Pacific near Tuvalu, Tokelau, and the Northern Cook Islands which are forecast to receive below normal rainfall in the coming three months.

Despite intermittent rainfall, significant drought that has existed in Tuvalu, Tokelau and the Northern Cook Islands is expected to continue through this period. Average or below average rainfall is expected for the Tuamotu Archipelago, Eastern Kiribati, Western Kiribati, the Society Islands, Samoa, Pitcairn Island.

The SPCZ is likely to be displaced southwest of normal during the forecast period. Above normal rainfall is likely for Vanuatu, Fiji, and Tonga. Near or above average rainfall is forecast for Papua New Guinea, the Solomon Islands, New Caledonia, Niue, the Southern Cook Islands and the Austral Islands. Near normal rainfall is expected for the Marquesas and Wallis & Futuna.
For the coming three months, cool sea surface anomalies are expected along and south of the Equator and also to the east of the Dateline encompassing Eastern Kiribati, Western Kiribati, the Northern Cook Islands, Tokealu and the Marquesas.

Below normal SSTs are expected for those island groups. Normal or below normal SSTs are forecast for Wallis & Futuna, Tuvalu, the Tuamotu Archipelago, the Society Islands, and Samoa.

Above normal SSTs are forecast for the Austral Islands and Southern Cook Islands. Near normal or above normal sea surface temperatures are forecast for Papua New Guinea, the Solomon Islands, New Caledonia, Vanuatu, Fiji, Tonga and Niue. Near normal SSTs are forecast for and Pitcairn Island.

The confidence for the rainfall outlook is moderately high. The average region–wide hit rate for rainfall forecasts issued in February is 66%, three percent higher than the long–term average for all months combined. The SST forecast uncertainty is greatest near the Marquesas and Eastern Kiribati. 

Rainfall anomaly outlook map for February to April 2012
SST anomaly outlook map for February to April 2012
Rainfall and sea surface termperature estimates for Pacific Islands for the next three months are given in the tables above. The tercile probabilities (e.g., 20:30:50) are derived from the averages of several global climate models. They correspond to the odds of the observed rainfall or sea surface temperatures being in the lowest one third of the distribution, the middle one third, or the highest one third of the distribution. For the long term average, it is equally likely (33% chance) that conditions in any of the three terciles will occur. *If conditions are climatology, we expect an equal chance of the rainfall being in any tercile.