Tropical rainfall and SST outlook: December 2009 to February 2010

During December 2009 – February 2010, a region of suppressed convection is likely in the southwest Pacific encompassing Niue, Tonga, New Caledonia, and Vanuatu. Below average rainfall is expected for all of those island groups. Near or below normal rainfall is expected for Fiji, Wallis & Futuna, the Southern Cook Islands, the Marquesas, and Pitcairn Island. Enhanced convection is likely along the Equator extending from Western to Eastern Kiribati, and also near Tokelau, with an expectation of above rainfall for those islands. Near normal rainfall is forecast for Papua New Guinea, Samoa, the Tuamotu Archipelago, and the Austral Islands.

The global models are continuing to show elevated temperatures in the near equatorial Pacific sea surface for the northern half of the Southwest Pacific. Most SST anomalies are consistent with the projections from last month. Above average sea surface temperatures are forecast for Eastern Kiribati. A region of near or above average sea surface temperatures is forecast around Papua New Guinea, the Solomon Islands, Western Kiribati, the Northern Cook Islands, the Marquesas and the Tuamotu archipelago. Near normal SSTs are forecast for the remainder of the southwest Pacific, except for Fiji, with near or below average SSTs.

The confidence in the multi-model ensemble forecast skill for this seasonal rainfall outlook is moderate to moderately high. In the past, the average region-wide hit rate for rainfall forecasts issued in December is 67%, 6% higher than the long-term average for all months combined. The SST forecast confidence is mostly high, but the greatest uncertainty is localised around the Marquesas and Eastern Kiribati.

Rainfall outlook map for December 2009 to January 2010

SST outlook map for December 2009 to January 2010