Tropical rainfall outlook: February to April 2005
Enhanced convection is forecast in the equatorial region of Western and Eastern Kiribati and Tokelau, where rainfall is expected to be above average. Above average or near average rainfall is forecast for Tuvalu, Northern Cook Islands, Austral Islands, and Pitcairn Island.
Suppressed convection is likely over the Solomon Islands, Vanuatu, New Caledonia, Fiji and Samoa, where rainfall is expected to be near average or below average. Below average rainfall is forecast for the Marquesas Islands of French Polynesia.
Rainfall is expected to be near average elsewhere in the region.
Rainfall outlook map for February to April 2005
Probabilities of rainfall departures from average
Broad-scale rainfall patterns and anomalies in the southern tropical Pacific area are estimated from the state of large-scale regional climate factors, such as La Niña or El Niño, their effect on the South Pacific and Tropical Convergence Zones, surface and sub-surface sea temperatures, and computer models of the global climate.
Rainfall estimates for the next three months for Pacific Islands are given in the adjacent 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.
The probabilities shown express the expected shift in the distribution from the long-term average, based on predictions of oceanic and atmospheric conditions. The amount of inter-model forecast consistency is indicated by the levels of confidence expressed in the table.
| Island group | Rainfall outlook | Outlook confidence |
|---|---|---|
| Western Kiribati | 15:35:50 (Above average) | Moderate – high |
| Eastern Kiribati | 25:30:45 (Above average) | Moderate – high |
| Tokelau | 15:35:50 (Above average) | Moderate – high |
| Tuvalu | 15:40:45 (Above or near average) | Moderate – high |
| Northern Cook Islands | 15:40:45 (Above or near average) | Moderate |
| Austral Islands | 15:40:45 (Above or near average) | Moderate |
| Pitcairn Island | 15:40:45 (Above or near average) | Moderate |
| Papua New Guinea | 35:45:20 (Near average) | Moderate |
| Wallis and Futuna | 30:40:30 (Near average) | Moderate |
| Tonga | 35:45:20 (Near average) | Moderate |
| Niue | 20:45:35 (Near average) | Moderate |
| Southern Cook Islands | 20:45:35 (Near average) | Moderate |
| Society Islands | 20:50:30 (Near average) | Moderate |
| Tuamotu Islands | 25:45:30 (Near average) | Moderate |
| Solomon Islands | 45:40:15 (Below or near average) | Moderate – high |
| Vanuatu | 45:40:15 (Below or near average) | Moderate – high |
| New Caledonia | 40:40:20 (Below or near average) | Low – moderate |
| Samoa | 40:35:25 (Below or near average) | Low |
| Fiji | 40:35:25 (Below or near average) | Moderate – high |
| Marquesas Islands | 45:35:20 (Below) | Low – moderate |
Rainfall outcomes as estimated from models and historical records. The third column indicates the probability of bottom (below), middle (average) or top (above) tercile rainfall, where a percentage is given. The rainfall outlook (second column) is subjectively estimated from the probabilities of bottom, middle and top terciles.