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Three-month outlook

Tropical rainfall outlook: August to October 2006

Rainfall outlook map for August to October 2006. (Click for enlargement)

Enhanced convection is expected to prevail over the Solomon Islands, where rainfall is likely to be above average.

Another large region of near or above average rainfall is expected from Vanuatu southeast to Pitcairn Island, including Wallis and Futuna, Tonga, Niue, the Southern Cook Islands, and the Society and Austral Islands.

Near or below average rainfall is likely over Tuamotu and the Marquesas Islands.

Suppressed convection is expected over Tuvalu and Tokelau, where rainfall is expected to be below average.

Near average rainfall is likely for the other countries in the region.

Confidence in the forecast model skill for this time of the year is about moderate for all the Pacific Island countries.

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

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.

Forecast validation: May to July 2006

Suppressed convection with below average rainfall was expected over Tokelau, with near or below average rainfall in Western and Eastern Kiribati, extending to Tuvalu, the Northern Cook Islands, and the Marquesas Islands. Average or above average rainfall was expected to extend from Papua New Guinea southeast to the Austral Islands, including Vanuatu, Tonga, and the Society Islands, with above average rainfall in Niue and the Southern Cook Islands. Near average rainfall was expected elsewhere in the region.

Areas of enhanced convection or above average rainfall affected the region near Papua New Guinea and the Solomon Islands, as well Niue, parts of Fiji, the Southern Cook Islands, and the Society and Austral Islands. Suppressed convection or below average rainfall occurred over New Caledonia, Wallis and Futuna, Tokelau, Eastern Kiribati, and Northern French Polynesia. Rainfall was higher than expected in the Solomon Islands and parts of Fiji, and lower than expected in Wallis and Futuna. Otherwise the overall rainfall anomaly pattern was similar to what was expected. The 'hit' rate for the May-July 2006 outlook was about 70%.