Tropical rainfall outlook: October to December 2006
The seasonal rainfall forecast patterns in the Pacific region are consistent with the developing El Niño conditions in equatorial Pacific Ocean.
Enhanced convection is likely in the equatorial region of Western and Eastern Kiribati and Tuvalu where rainfall is expected to be above average. Rainfall is expected to be near or above average over Tokelau, Northern Cook Islands and Pitcairn Island.
Suppressed convection with below average rainfall is likely over New Caledonia while near or below average rainfall is expected over Papua New Guinea, Vanuatu, Fiji, Tonga, Niue, and the Marquesas Islands.
Near average rainfall is expected elsewhere in the region.
Confidence in the forecast model is around moderate to high for this time of the year.
| Island group | Rainfall outlook | Outlook confidence |
|---|---|---|
| Western Kiribati | 20:30:50 (Above average) | Moderate - high |
| Eastern Kiribati | 20:30:50 (Above average) | Moderate - high |
| Tuvalu | 25:30:45 (Above average) | Moderate - high |
| Tokelau | 20:40:40 (Average or above) | Moderate |
| Northern Cook Islands | 20:40:40 (Average or above) | Moderate |
| Pitcairn Island | 20:40:40 (Average or above) | Moderate |
| Solomon Islands | 20:45:35 (Near average) | Moderate |
| Samoa | 35:45:20 (Near average) | Moderate |
| Wallis & Futuna | 30:40:30 (Near average) | Moderate |
| Tuamotu Islands | 30:45:25 (Near average) | Moderate |
| Southern Cook Islands | 30:40:30 (Near average) | Moderate |
| Society Islands | 25:50:25 (Near average) | Moderate |
| Austral Islands | 25:45:30 (Near average) | Moderate |
| Papua New Guinea | 45:40:15 (Average or below) | Moderate |
| Vanuatu | 40:40:20 (Average or below) | Moderate |
| Fiji | 40:40:20 (Average or below) | Moderate |
| Tonga | 40:40:20 (Average or below) | Moderate |
| Niue | 40:40:20 (Average or below) | Low – moderate |
| Marquesas Islands | 45:40:15 (Average or below) | Moderate – high |
| New Caledonia | 45:30:25 (Below average) | 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.
Forecast validation: July to September 2006
Areas of suppressed convection and below average rainfall were expected over Tuvalu and the Marquesas Islands, and near or below average rainfall was expected over Tokelau. A large region of enhanced convection and average or above average rainfall was expected to extend from Papua New Guinea southeast to Pitcairn Island, including the Solomon Islands, Vanuatu, Wallis and Futuna, Fiji, Tonga, Niue, the Southern Cook Islands, the Society Islands, and the Austral Islands. Near average rainfall was expected elsewhere.
Areas of enhanced convection or above average rainfall affected the region near Papua New Guinea and over the Solomon Islands, as well as parts of French Polynesia and the Southern Cook Islands. Below average rainfall occurred over New Caledonia and the Northern Cook Islands. Rainfall was higher than expected in parts of French Polynesia and Samoa and lower than expected in Fiji, Tonga, and Niue. The ‘hit’ rate for the July-September 2006 outlook was about 70%.