Tropical rainfall and SST outlook: October to December 2010

During October – December 2010, a region of suppressed convection is likely in the southwest Pacific encompassing...

During October – December 2010, a region of suppressed convection is likely in the southwest Pacific encompassing Eastern Kiribati, Tuvalu, the Marquesas, the Northern Cook Islands and Western Kiribati. Below average rainfall is expected for those island groups. Tokelau is expected to receive near or below normal rainfall. Enhanced convection is likely along the Southwest Pacific Convergence Zone displaced southwest of its normal position. Papua New Guinea, New Caledonia, Niue, the Southern Cook Islands, Tonga and Vanuatu expected to receive above normal rainfall during this time. Near or above average rainfall is forecast for Fiji, Wallis & Futuna, Samoa and the Austral Islands. Near normal rainfall is forecast for the Society Islands and the Solomon Islands. No clear precipitation guidance is offered for Pitcairn Island or the Tuamotu Archipelago.  

Many global models continue to show strong near equatorial Pacific sea surface temperature anomalies in the coming months, and a cold tongue extending from east to west across the Date line. Above average SSTs are forecast for Vanuatu, New Caledonia, Fiji, the Southern Cook Islands and the Austral Islands. Average or above average sea surface temperatures are forecast for Papua New Guinea, Niue, Tonga, Wallis & Futuna, the Society Islands, and Pitcairn Island. 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 Samoa, the Solomon Islands and the Tuamotu Archipelago.  

The forecast confidence for this rainfall outlook is moderately high. The average region-wide hit rate for rainfall forecasts issued in October is 64%, 3% higher than all months combined. The SST forecast confidence is mostly moderately high, but the greatest uncertainty is localised around the Equator.

Rainfall outlook map for October to December 2010


SST outlook map for October to December 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 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.