Tropical rainfall and SST outlook: February to April 2013

The tropical Pacific is currently slightly cooler than normal along the Equator to the east of the Dateline, and warmer to the west. The dynamical models indicate that both the ITCZ and the SPCZ will be situated south of their climatological positions for February 2012 – April 2013.

Slightly drier than normal conditions are likely to affect areas south of the Equator to the east of the Dateline, while wetter than normal conditions are likely in the western equatorial Pacific.

Near or above normal rainfall is forecast the Federated States of Micronesia, Pitcairn Island and Tonga.

Near normal rainfall is expected for the Austral islands, the Southern Cook Islands, Fiji, New Caledonia, Niue, Papua New Guinea, Samoa, the Solomon Islands, Wallis & Futuna and Vanuatu.

Normal or below normal rainfall is forecast the Tuamotu archipelago, Tuvalu, Eastern Kiribati and Western Kiribati and Tokelau. Below normal rainfall is forecast for the Northern Cook Islands and the Marquesas. No clear guidance is available for the Society Islands.

The global model ensemble shows patterns similar to a weak La Niña in the SST field along the Equator. Cooler than normal SST are forecast the eastern Pacific Ocean while warmer than normal SSTs are expected west of the Dateline.

Near normal or above normal SSTs are forecast for Papua New Guinea, the Solomon Islands, Fiji, Niue, Tonga and Vanuatu.

Near normal or below normal SSTs are forecast for the Marquesas and eastern Kiribati. Normal SSTs are forecast elsewhere.

The confidence for the rainfall outlook is moderate to high. The average region–wide hit rate for rainfall forecasts issued in February is 66%, three points higher than the long–term average for all months combined.

The SST forecast confidence is high across the region except for the Marquesas and Eastern Kiribati, where uncertainty is greater. 

Rainfall anomaly map for February to April 2013
SST anomaly outlook map for February to April 2013
NOTE: Rainfall and sea surface termperature estimates for Pacific Islands for the next three months are given in the tables below. 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.