Tropical rainfall and SST outlook: January to March 2011

During January – March 2011, a region of suppressed convection is likely in the southwest Pacific encompassing...

During January – March 2011, a region of suppressed convection is likely in the southwest Pacific encompassing Eastern Kiribati, Tuvalu, Tokelau, the Northern Cook Islands and Western Kiribati. Below average rainfall is expected for those island groups. Average or below average rainfall is expected for the Marquesas, Pitcairn Island, the Society Islands, Tuamotu, the Solomon Islands, and Papua New Guinea. Enhanced convection is likely along the Southwest Pacific Convergence Zone, which is expected to be displaced to the southwest of normal. Fiji, New Caledonia, Niue, Tonga, and

Vanuatu are expected to receive above normal rainfall for the coming three month period. Near or above average rainfall is forecast for Wallis & Futuna, the Southern Cook Islands, and the Austral Islands. No clear precipitation guidance is offered for Samoa.

The ensemble of global models show negative equatorial Pacific sea surface temperature anomalies in the coming months, but the warm signal in the sub-tropics appears weaker than in previous months forecasts. Above average SSTs are forecast for New Caledonia and the Austral Islands. Average or above average sea surface temperatures are forecast for Papua New Guinea, Vanuatu, Fiji, Tonga, and Niue. Near or below normal SSTs are forecast for the Northern Cook Islands, the Southern Cook Islands, the Society Islands, the Tuamotu Archipelago, Tuvalu and Tokelau. Below normal SSTs are anticipated for Western Kiribati, Eastern Kiribati, and the Marquesas. Near normal SSTs are forecast for Samoa, the Solomon Islands, Wallis & Futuna, and Pitcairn Island.

The forecast confidence for the rainfall outlook is moderately high. The average region–wide hit rate for rainfall forecasts issued in January is 58%, 2% lower than all months combined. The SST forecast confidence is mostly high or moderate-to- high, with uncertainty localised near Eastern Kiribati and the Marquesas.

Rainfall anomaly outlook map for January to March 2011



SST anomaly outlook map for January to March 2011


NOTE: 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.