During September – November 2010, a region of suppressed convection is likely in the southwest Pacific encompassing Eastern Kiribati, Tuvalu, the Marquesas and Western Kiribati.
Below average rainfall is expected for those island groups. Pitcairn Island, Tokelau, and the Tuamotu Archipelago are expected to receive near or below normal rainfall. Enhanced convection is likely along the Southwest Pacific Convergence Zone displaced southwest of its normal position, and Fiji, New Caledonia, Niue, Samoa, Tonga and Vanuatu expected to receive above normal rainfall during Austral spring. Near or above average rainfall is forecast for the Northern Cook Islands, the Southern Cook Islands Wallis & Futuna, and the Austral Islands. Near normal rainfall is forecast for the Society Islands and the Solomon Islands. No clear precipitation guidance is offered for Papua New Guinea.
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 across the Date line. Above average SSTs are forecast for Niue and Tonga, while average or above average sea surface temperatures are forecast for Papua New Guinea, New Caledonia, Vanuatu, the Northern Cook Islands, the Austral Islands, Fiji, Wallis & Futuna, and the Southern Cook Islands. Near or below normal SSTs are forecast for the Northern Cook Islands, Tuvalu and Tokelau, while below normal SSTs are expected for Western Kiribati, Eastern Kiribati, and the Marquesas. 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 September is 67%, 6% higher than all months combined. The SST forecast confidence is mostly moderately high, but the greatest uncertainty is localised around the International Date Line, the Solomon Islands and French Polynesia.
Rainfall outlook map for September to November 2010
SST outlook map for September to November 2010
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 he 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.