Tropical rainfall outlook: July to September 2008
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.