Tropical rainfall outlook: January to March 2006
A large area of enhanced convection is expected from Vanuatu east southeast to Pitcairn Island, including Samoa, Fiji, Tonga, Niue, and the Society and Austral Islands, where rainfalls are likely to be near or above average. The Southern Cook Islands is expected to experience above average rainfall.
Near or below average rainfall is likely from Tuvalu east to the Marquesas Islands, including Tokelau, the Northern Cook Islands, and the Tuamotu Islands. Below average rainfall is expected over Western and Eastern Kiribati. Near average rainfall is expected elsewhere in the region.
The Southwest Pacific tropical cyclone season is well underway, although there have been no occurrences to date. In both January and February, risk increases, as there are usually two to three tropical cyclone occurrences per month. About nine tropical cyclones can be expected on average, for the complete season over the entire Southwest Pacific region in ENSO-neutral seasons similar to the present. The February issue of the ICU will provide information on any occurrences of tropical cyclones in the region.
| Island group | Rainfall outlook | Outlook confidence |
|---|---|---|
| Southern Cook Islands | 20:30:50 (Above average) | Moderate |
| Vanuatu | 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 | 10:40:50 (Near or above average) | Moderate |
| Society Islands | 15:40:45 (Near or above average) | Moderate |
| Austral Islands | 15:40:45 (Near or above average) | Moderate |
| Pitcairn Island | 20:40:40 (Near or above average) | Moderate |
| Papua New Guinea | 30:50:20 (Near average) | Moderate |
| Solomon Islands | 30:50:20 (Near average) | Moderate |
| Wallis & Futuna | 20:45:35 (Near average) | Moderate |
| New Caledonia | 35:35:30 (Climatology) | Moderate |
| Tuvalu | 45:40:15 (Near average or below) | Moderate |
| Tokelau | 45:40:15 (Near average or below) | Moderate |
| Northern Cook Islands | 40:40:20 (Near average or below) | Moderate |
| Tuamotu Islands | 40:40:20 (Near average or below) | Moderate |
| Marquesas Islands | 40:40:20 (Near average or below) | Moderate |
| Western Kiribati | 50:30:20 (Below average) | Moderate |
| Eastern Kiribati | 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: October to December 2005
Enhanced convection, with average or above average rainfall, was expected over Papua New Guinea and the Solomon Islands, as well as from Samoa to central and southern French Polynesia, including Niue and the Northern and Southern Cook Islands. Suppressed convection was expected over the equatorial region of Eastern Kiribati with below average rainfall. Near or below average rainfall was expected in Western Kiribati and Tuvalu. Near average rainfall was expected elsewhere in the region.
Areas of average or above average rainfall affected Papua New Guinea and the Solomon Islands, as well as Fiji, Tonga, American Samoa, and the Marquesas Islands. Suppressed convection, or below average rainfall, occurred over Western and Eastern Kiribati, extending to Vanuatu and New Caledonia, as well as the Northern Cook Islands and central French Polynesia. Rainfall was higher than expected in Tonga and the Marquesas Islands, and lower than forecast in New Caledonia, Vanuatu, Wallis and Futuna, and the Society Islands. The overall 'hit' rate for the October to December 2005 rainfall outlook was about 70%. Outcomes for the Solomon Islands (based on OLR anomalies) have been consistent with forecasts for 11 consecutive months.