Tropical rainfall and SST outlook: June to August 2010
During June – August 2010, a region of suppressed convection is likely in the southwest Pacific encompassing Eastern Kiribati, the Marquesas, Pitcairn Island and Fiji. Near or below average rainfall is expected for those island groups, respectively. Enhanced convection is likely along the region close to the normal position of the South Pacific Convergence Zone. Above average rainfall is expected for Papua New Guinea, the Solomon Islands, and Samoa. Near or above average rainfall is forecast for The Northern Cook Islands, The Southern Cook Islands, The Austral Islands, Tuvalu, Tokelau, Vanuatu and Wallis & Futuna. Near normal rainfall is forecast New Caledonia, Tonga, and the Tuamotu Archipelago. No clear precipitation guidance is offered for Niue or Western Kiribati.
Most global models have shown a shift in the near equatorial Pacific sea surface temperatures to cold anomalies near Eastern Kiribati in the coming months. In a comparison to last months forecast information, the equatorial surface water cold tongue has extended from east to west, and is encroaching on or crossing the Dateline in some models. For June to August 2010, average or above average sea surface temperatures are forecast for Papua New Guinea, the Solomon Islands, Vanuatu, the Northern Cook Islands, The Austral Islands, Tuvalu and Tokelau. No clear SST guidance is offered for The Southern Cook 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 moderate to moderately high. In the past, the average region-wide hit rate for rainfall forecasts issued in June is 60%, 1% lower than the long–term average for all months combined. The SST forecast confidence is mostly moderately high, but the greatest uncertainty is localised around Western Kiribati and Eastern Kiribati.
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.