Tropical rainfall outlook: May to July 2006.
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%.