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Three-month outlook

Tropical rainfall outlook: May to July 2006.

Rainfall outlook map for May to July 2006. (Click for enlargement)

Although equatorial SSTs have returned to a neutral ENSO state, there is a lag in atmospheric conditions and rainfall in the southwest Pacific region still depicts La Niña like patterns.

Enhanced convection is expected over Niue and the Southern Cook Islands, where rainfall is expected to be above average. A large region of near or above average rainfall is expected from Papua New Guinea extending eastwards to the Austral Islands, including Vanuatu, Tonga, and the Society Islands.

Suppressed convection is likely over Tokelau, where rainfall is forecast to be below average. Near or below average rainfall is expected in the equatorial region of Western Kiribati east to the Marquesas Islands, including Eastern Kiribati, Tuvalu, and the Northern Cook Islands.

As the tropical cyclone season ends and the dry season approaches, the rainfall forecast model skills are expected to be in the low to moderate range.

Island group Rainfall outlook Outlook confidence
Niue 15:30:55 (Above average) Moderate
Southern Cook Islands 15:35:50 (Above average) Moderate
Papua New Guinea 10:40:50 (Near or above average) Moderate
Vanuatu 15:40:45 (Near or above average) Moderate
Tonga 15:40:45 (Near or above average) Low – moderate
Society Islands 20:40:40 (Near or above average) Low – moderate
Austral Islands 20:40:40 (Near or above average) Low – moderate
Solomon Islands 20:45:35 (Near average) Low
New Caledonia 25:40:35 (Near average) Low
Wallis & Futuna 25:50:25 (Near average) Moderate
Fiji 25:45:30 (Near average) Low – moderate
Samoa 25:50:25 (Near average) Moderate
Tuamotu Islands 30:40:30 (Near average) Low – moderate
Pitcairn Island 20:50:30 (Near average) Moderate
Western Kiribati 40:40:20 (Near or below average) Low
Eastern Kiribati 45:40:15 (Near or below average) Low – moderate
Tuvalu 40:40:20 (Near or below average) Low – moderate
Northern Cook Islands 45:40:15 (Near or below average) Low – moderate
Marquesas Islands 40:40:20 (Near or below average) Low – moderate
Tokelau 55:25:20 (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: February to April 2006

Suppressed convection with below average rainfall was expected in the equatorial region of Western and Eastern Kiribati, with near or below average rainfall from Tuvalu east to the Marquesas Islands. A large region of near or above average rainfall was expected over Fiji east to the Austral Islands, including Tonga, Niue, the Northern and Southern Cook Islands, and the Society Islands. Near average rainfall is expected elsewhere in the region.

Areas of enhanced convection and above average rainfall affected Samoa, parts of Tonga, Niue, and the Austral and Marquesas Islands. Suppressed convection or below average rainfall occurred over Western Kiribati, Tuvalu, and the Tuamotu Islands. Rainfall was higher than expected in Eastern Kiribati, Samoa, and Niue, and lower than forecast in parts of Fiji. The 'hit' rate for the February-April 2006 outlook was about 70%.