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Three-month outlook

Tropical rainfall outlook: July to September 2008

Rainfall outlook map for July to September 2008. (Click for enlargement)

La Niña conditions have dissipated, but residual effects are still likely to have an influence on rainfall patterns during the July–September 2008 forecast period. A large region of suppressed convection is very likely in the southwest Pacific encompassing the Northern Cook Islands, Tuamotu, the Society Islands, the Austral Islands, and the Marquesas. Average rainfall is likely for New Caledonia and Samoa.

Enhanced convection is likely from Papua New Guinea extending southeastward toward Vanuatu, through to the Southern Cook Islands, including Fiji, Niue, and Tonga. Above average rainfall is expected in those countries for the coming three-month period. No clear precipitation guidance is offered for Eastern Kiribati, Pitcairn Island, the Solomon Islands, and Wallis & Futuna.

The confidence in the forecast model skill for this seasonal outlook is moderate to moderately high for most Pacific Island countries. In the past, the average region-wide hit rate for forecasts issued in July is 67%, 6% higher than the long-term average for all months combined.

Island group Rainfall outlook Outlook confidence
Tonga 20:30:50 (Above) Moderate - high
Cook Islands (Southern) 20:35:45 (Above) Moderate - high
Niue 20:35:45 (Above) Moderate - high
Papua New Guinea 20:35:45 (Above) Moderate - high
Kiribati (Western) 30:30:40 (Above) Moderate
Tokelau 30:30:40 (Above) Moderate
Tuvalu 30:30:40 (Above) Moderate
Fiji 25:35:45 (Near to above) Moderate - high
Vanuatu 20:40:40 (Near to above) Moderate - high
New Caledonia 30:40:30 (Near normal) Moderate
Samoa 30:40:30 (Near normal) Moderate
Kiribati (Eastern) 30:35:35 (Climatology*) Moderate
Pitcairn Islands 30:35:35 (Climatology*) Moderate
Solomon Islands 35:35:30 (Climatology*) Moderate - high
Wallis & Futuna 35:35:30 (Climatology*) Moderate - high
Austral Islands 45:30:25 (Below) Moderate
Society Islands 45:35:20 (Below) Moderate
Tuamotu Islands 50:30:20 (Below) Moderate
Marquesas Islands 55:30:15 (Below) Moderate - high
Cook Islands (Northern) 60:30:10 (Below) Moderate - high

NOTE: Rainfall estimates for Pacific Islands for the next three months are given in the table. The tercile probabilities (e.g., 20:30:50) are derived from the interpretation of several global climate models. They correspond to the odds of the observed rainfall being in the lowest (driest) one third of the rainfall distribution, the middle one third, or the highest (wettest) one third of the distribution. On the long-term average, rainfall is equally likely (33% chance) in any tercile.