Tropical rainfall and SST outlook: August to October 2010

During August – October 2010, suppressed convection is likely in the southwest Pacific encompassing the Marquesas, the Tuamotu Archipelago, Eastern Kiribati, Pitcairn Island, and Western Kiribati.

Near or below average rainfall is expected for those island groups, except for Eastern Kiribati and Western Kiribati where below normal rainfall is forecast. Enhanced convection is likely near the Equator in the far western Southwest Pacific, with Papua New Guinea, the Solomon Islands, Vanuatu, Wallis & Futuna and Samoa expected to receive above normal rainfall. Near or above average rainfall is forecast for the Northern Cook Islands, the Southern Cook Islands, Niue, Fiji and New Caledonia. Near normal rainfall is forecast for Tuvalu and the Austral Islands. No clear precipitation guidance is offered for Tokelau or the Society Islands.

Many global models continue to show strengthening in the near equatorial Pacific sea surface temperature anomalies in the coming months, and propagation of a cold tongue from east to west toward the Date line. Above average SSTs are forecast for the Southern Cook Islands, New Caledonia and Vanuatu, while average or above average sea surface temperatures are forecast for Papua New Guinea, the Northern Cook Islands, the Austral Islands, Tokelau, Tuvalu and Wallis & Futuna. Below normal SSTs are forecast for the Marquesas, Eastern Kiribati, and Western Kiribati. is expected to experience below normal SSTs. No clear SST guidance is offered for Fiji, Niue, the Society Islands, and Tonga. Near normal SSTs are forecast for the remainder of the southwest Pacific.

The forecast confidence for this rainfall outlook is moderately high. The average region-wide hit rate for rainfall forecasts issued in August is 61%, equal to the long–term average for all months combined. The SST forecast confidence is mostly moderately high, but the greatest uncertainty is localised around the International Date Line and near the Equator..

Rainfall outlook map for August to October 2010

SST outlook map for August to October 2010