Tropical rainfall outlook: March to May 2005
Weakening El Niño conditions are expected to continue influencing the climate patterns in the Pacific region over the coming months.
Enhanced convection is expected over the equatorial Pacific region, where rainfall is forecast to be above average for Western Kiribati. Enhanced convection with average or above average rainfall is over Eastern Kiribati, Tokelau and Tuvalu, as well as the Austral Islands and Pitcairn Island.
Suppressed convection is likely over Fiji and the Marquesas Islands, where rainfall is expected to be near or below average.
Rainfall is forecast to be near average for the rest of the region, with generally moderate model skills for this time of the year.
Rainfall outlook map for March to May 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 | 25:30:45 (Above) | Moderate – high |
| Eastern Kiribati | 15:45:40 (Near average or above) | Moderate |
| Tuvalu | 20:40:40 (Near average or above) | Moderate |
| Tokelau | 20:40:40 (Near average or above) | Moderate |
| Austral Islands | 20:40:40 (Near average or above) | Moderate |
| Pitcairn Island | 20:40:40 (Near average or above) | Moderate |
| Papua New Guinea | 30:45:25 (Near average) | Moderate |
| Solomon Islands | 30:50:20 (Near average) | Moderate |
| Vanuatu | 30:45:25 (near average) | Moderate |
| Wallis and Futuna | 25:50:25 (Near average) | Moderate |
| Samoa | 20:50:30 (Near average) | Moderate |
| Tonga | 30:45:25 (Near average) | Moderate |
| Niue | 25:45:30 (Near average) | Moderate |
| Northern Cook Islands | 25:45:30 (Near average) | Moderate |
| Southern Cook Islands | 20:50:30 (Near average) | Moderate |
| Society Islands | 30:45:25 (Near average) | Moderate |
| New Caledonia | 35:40:25 (Near average) | Low – moderate |
| Tuamotu Islands | 35:40:25 (Near average) | Moderate |
| Fiji | 40:40:20 (Below or near average) | Low – moderate |
| Marquesas Islands | 40:35:25 (Below or near 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.