Tropical rainfall outlook: December 2005 to February 2006
A large region of enhanced convection is expected from the Solomon Islands southeast to the Austral Islands including Vanuatu, Wallis and Futuna, Samoa, Fiji Tonga, Niue, Southern Cook Islands, and Society Islands.
Near or below average rainfall is likely over Tuvalu, Tokelau, and Pitcairn Island. Suppressed convection resulting in below average rainfall is likely in the equatorial region of Western and Eastern Kiribati, the Northern Cook Islands, and the Marquesas Islands.
The Southwest Pacific tropical cyclone season began in November, and so far there have been no occurrences. However, on average, there is a 70% chance that at least one tropical cyclone will occur in the southwest Pacific before 1 January. Last season the first tropical cyclone occurred about Christmas Day. Tropical cyclone risk increases, to average two to three occurrences per month, in January and February. On the basis of previous ENSO-neutral seasons, about nine tropical cyclones can be expected, on average, for the complete season over the entire Southwest Pacific region (see ICU issue no. 61 for more detail). The January issue of the ICU will provide information on relating to any occurrences of tropical cyclones in the region.
| Island group | Rainfall outlook | Outlook confidence |
|---|---|---|
| Solomon Islands | 15:40:45 (Near or above average) | Moderate |
| Vanuatu | 20:40:40 (Near or above average) | Moderate |
| Wallis & Futuna | 20:40:40 (Near or above average) | Moderate |
| Samoa | 20:40:40 (Near or above average) | Moderate |
| Fiji | 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 |
| Papua New Guinea | 20:50:30 (Near average) | Moderate |
| New Caledonia | 35:35:30 (Near average) | Low – moderate |
| Pitcairn Island | 20:45:35 (Near average) | Moderate |
| Tuvalu | 40:40:20 (Near or below average) | Moderate |
| Tokelau | 40:40:20 (Near or below average) | Moderate |
| Tuamotu Islands | 40:40:20 (Near or below average) | Moderate |
| Western Kiribati | 50:30:20 (Below average) | Moderate |
| Eastern Kiribati | 50:30:20 (Below average) | Moderate |
| Northern Cook Islands | 45:30:25 (Below average) | Moderate |
| Marquesas Islands | 50:30:20 (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: September to November 2005
Enhanced convection with above average rainfall was expected over the Solomon Islands, with average or above average rainfall over Papua New Guinea, as well as Samoa, Niue, the Southern Cook Islands, Tuamotu Islands, and Marquesas Islands. Suppressed convection was expected over Eastern Kiribati, extending to Tuvalu, Vanuatu, and Fiji. Near average rainfall was forecast elsewhere in the region.
Areas of enhanced convection or above average rainfall affected Papua New Guinea and the northwest of the Solomon Islands, as well as the region from Niue east to the Southern Cook Islands. Suppressed convection or below average rainfall occurred in Western and Eastern Kiribati, Tuvalu, Tokelau, and the Northern Cook Islands. Rainfall was higher than expected in Tonga, and lower than forecast in New Caledonia, Tokelau, and the Society Islands. The overall 'hit' rate for the September – November 2005 rainfall outlook was very high, being about 75%. Outcomes for the Solomon Islands (based on OLR anomalies) have been consistent with forecasts for ten consecutive months.