Tropical rainfall outlook: March to May 2006.
ENSO indicators in the equatorial Pacific are showing weakening La Niña conditions for the coming months. Global climate models are echoing this in the coming three month rainfall forecast patterns.
Suppressed convection is expected in the equatorial region around the Date Line where rainfall is expected to be below average for Western Kiribati and Tuvalu. Near or below average rainfall is likely over Eastern Kiribati and Tokelau.
A large region of enhanced convection with near or above average rainfall is expected from Papua New Guinea southeastwards to Pitcairn Island, including Vanuatu, Wallis & Futuna, Tonga, Niue, the Southern Cook Islands, as well as Society and Austral Islands.
Near average rainfall is likely elsewhere in the region. As this is the transition period from the wet to dry season, the forecast model skills are expected to be low or moderate for most countries in the region.
| Island group | Rainfall outlook | Outlook confidence |
|---|---|---|
| Papua New Guinea | 15:45:40 (Near or above average) | Moderate |
| Vanuatu | 15:40:45 (Near or above average) | Moderate |
| Wallis & Futuna | 15:45:40 (Near or above average) | Low – moderate |
| Tonga | 20:40:40 (Near or above average) | Low – moderate |
| Niue | 20:40:40 (Near or above average) | Low – moderate |
| Southern Cook Islands | 20:40:40 (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 |
| Solomon Islands | 30:40:30 (Near average) | Moderate |
| New Caledonia | 25:45:30 (Near average) | Moderate |
| Fiji | 20:45:35 (Near average) | Low – moderate |
| Samoa | 30:40:30 (Near average) | Moderate |
| Northern Cook Islands | 25:45:30 (Near average) | Moderate |
| Tuamotu Islands | 30:45:25 (Near average) | Moderate |
| Marquesas Islands | 30:45:25 (Near average) | Moderate |
| Eastern Kiribati | 40:40:20 (Near or below average) | Moderate |
| Tokelau | 40:40:20 (Near or below average) | Moderate |
| Western Kiribati | 45:35:20 (Below average) | Moderate |
| Tuvalu | 45:30:25 (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: January to March 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, including Tokelau, the Northern Cook Islands, and the Tuamotu Islands. A large region of near or above average rainfall was expected from Vanuatu southeast to Pitcairn Island including Samoa, Fiji, Tonga, Niue, the Society Islands, the Austral Islands, and the Southern Cook Islands. Near average rainfall was expected elsewhere in the region.
Areas of enhanced convection and above average rainfall affected the Solomon Islands, Samoa, parts of Fiji, Tonga, Southern Cook Islands, Niue, and the Austral Islands. Suppressed convection or below average rainfall occurred over Western and Eastern Kiribati, Vanuatu, Tuvalu, the Northern Cook Islands, and Tuamotu Islands. Rainfall was higher than expected in the Solomon Islands, and lower than forecast in Vanuatu. The overall rainfall outcome was similar to what was expected, with a very high 'hit' rate for the January-March 2006 outlook of about 80%.