Tropical rainfall and SST outlook: August to October 2009

Rainfall outlook map for August to October 2009.
Sea surface temperature outlook map for August to October 2009.
During August – October 2009, a region of suppressed convection is likely in the southwest Pacific encompassing Tokelau, the Northern Cook Islands, and the Marquesas, with below average rainfall expected for those areas. Near to below average rainfall is expected for Papua New Guinea and the Society Islands. Near normal rainfall is forecast for Niue, the Tuamotu Archipelago, New Caledonia, and Pitcairn Island.

Rainfall outlook map for August to October 2009.
Sea surface temperature outlook map for August to October 2009.

During August – October 2009, a region of suppressed convection is likely in the southwest Pacific encompassing Tokelau, the Northern Cook Islands, and the Marquesas, with below average rainfall expected for those areas. Near to below average rainfall is expected for Papua New Guinea and the Society Islands. Near normal rainfall is forecast for Niue, the Tuamotu Archipelago, New Caledonia, and Pitcairn Island. Enhanced convection is likely along the Equator extending from Western to Eastern Kiribati, and in the area around the Southern Cook Islands and the Austral Islands. These regions are expected to receive near or above normal rainfall, with Western Kiribati forecast to receive above normal rainfall. No clear precipitation guidance is offered for Fiji, Vanuatu, Tuvalu, Tonga, Samoa, Wallis & Futuna, and the Solomon Islands. The global models have a exhibited an increase in the near equatorial Pacific sea surface temperatures for the northwest corner of the Southwest Pacific. For August – October 2009, above average temperatures are forecast for Eastern Kiribati. A region of near or above average sea surface temperatures are forecast around Papua New Guinea, the Solomon Islands, Western Kiribati, the Northern Cook Islands, the Marquesas and the Society Islands.  Near normal SSTs are forecast for the remainder of the southwest Pacific. The confidence in the multi-model ensemble forecast skill for this seasonal rainfall outlook is moderately high for most Pacific Island countries. In the past, the average region-wide hit rate for rainfall forecasts issued in August is 61%, equivalent to the long-term average for all months combined. The SST forecast confidence is mostly high for this period, but the greatest uncertainty localised around the Marquesas and Eastern Kiribati.