Tropical rainfall and SST outlook: August to October 2012

The Tropical Pacific is currently on the brink of El Niño, but the atmosphere is still not fully coupled to the ocean and atmospheric circulation anomalies typical of El Niño are not yet present. Convection and rainfall is still higher than normal in the western Pacific over the Maritime Continent.

The ITCZ is south of its normal position to the east of the Dateline, with above normal rainfall over the Equator and below normal rainfall further north.

For the period August to October 2012, the dynamical models used in METPI indicate near or above normal rainfall for Western and Eastern Kiribati, Tonga, and Pitcairn Island.

Near normal rainfall is expected for the Austral Islands, the Cook Islands, New Caledonia, Papua New Guinea, Tuvalu, the Marquesas, and Vanuatu.

Normal or below normal rainfall is forecast for Fiji, Samoa, the Society Islands, the Tuamotu Islands and Wallis & Futuna. No clear guidance is offered for the Solomon Islands and Niue.

The global model ensemble continues to show the development of El Niño–like sea surface temperature (SST) signals, with east to west extension of warm anomalies in the equatorial region to the east of the Dateline in the coming three months.

Above normal SSTs are forecast for Eastern Kiribati, while near normal or above normal SSTs are forecast for Western Kiribati, the Austral Islands, the Northern Cook Islands, Niue, Papua New Guinea, the Solomon Islands and the Tuamotu Islands.

Near normal SSTs are forecast for the Southern Cook Islands, Fiji, the Marquesas, New Caledonia, PItcairn Island, Samoa, the Society Islands, Tokelau, Tonga, Tuvalu, Vanuatu and Wallis & Futuna.

The confidence for the rainfall outlook is moderate to high. The average region–wide hit rate for rainfall forecasts issued in August is 60%, 3 points lower than the long–term average for all months combined.

The SST forecast confidence is moderate to high across the region, and uncertainty is greatest near Eastern and Western Kiribati. 

Rainfall anomaly outlook map for August to October 2012
SST anomaly outlook map for August to October 2012
Rainfall and sea surface temperature 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.