Three-month outlook
Rainfall outlook for February to April 2003
Above average or average rainfall in equatorial latitudes from west to east and the Solomon Islands trending southeast to Society Islands.
Below average or average rainfall from Vanuatu, Fiji, New Caledonia, trending east to the Marquesas Islands and Pitcairn Island.
Near average rainfall likely elsewhere.
Rainfall is expected to be above average in the equatorial Pacific from west to east due to continuing enhanced convection, resulting in above average rainfall in Western and Eastern Kiribati and the Solomon Islands. Average or above average rainfall is the likely outcome from Tuvalu trending east-southeast to Samoa, Northern Cook Islands and Society Islands.
Below average or average rainfall is likely from Vanuatu east to Austral Islands including Fiji and Tonga. Below average rainfall is expected in New Caledonia, the Marquesas and the Pitcairn Islands. Near average rainfall is expected elsewhere in the region.
The forecast model skills for the current outlook are generally moderate or high for most islands in the region.
Rainfall outlook map for February to April 2003
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 | Confidence in the Outlook | |
|---|---|---|---|
| Western Kiribati | 20:20:60 | (Above) | High |
| Eastern Kiribati | 20:20:60 | (Above) | High |
| Solomon Islands | 20:30:50 | (Above) | Moderate |
| Tuvalu | 20:35:45 | (Average or above average) | Moderate |
| Tokelau | 20:35:45 | (Average or above average) | Moderate |
| Wallis & Futuna | 15:45:40 | (Average or above average) | Moderate |
| Samoa | 15:40:45 | (Average or above average) | Moderate |
| Northern Cook Islands | 20:45:35 | (Average or above average) | Moderate |
| Society Island | 20:45:35 | (Average or above average) | Moderate |
| Papua New Guinea | 20:50:30 | (Near average) | Low |
| Niue | 30:50:20 | (Near average) | Moderate – High |
| Southern Cook Islands | 25:50:25 | (Near average) | Moderate |
| Vanuatu | 50:40:10 | (Average or below average) | Moderate |
| Fiji | 40:40:20 | (Average or below average) | Moderate – High |
| Tonga | 40:35:25 | (Average or below average) | Moderate |
| Austral Islands | 40:40:20 | (Average or below average) | Moderate |
| New Caledonia | 45:40:15 | (Below average) | Moderate |
| Marquesas | 50:30:20 | (Below averge) | Moderate |
| Pitcairn Island | 50:30:20 | (Below average) | 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.