Tropical rainfall outlook: June to August 2005
The Pacific region will continue to see the lingering effects of the warm event which dissipated earlier this year, especially on the rainfall patterns.
Based on the model guidance, enhanced convection is expected over Eastern Kiribati, where rainfall is forecast to be above average. Western Kiribati and Tuvalu are expected to experience near or above average rainfall.
Near or below average rainfall is expected over Fiji and the Marquesas Islands of French Polynesia. Near average rainfall is forecast for the rest of the countries in the region.
The skill of the models is reduced during this time of the year, as the dry season commences.
Rainfall outlook map for June to August 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 |
|---|---|---|
| Eastern Kiribati | 20:30:45 (Above) | Low – moderate |
| Western Kiribati | 15:45:40 (Near average or above) | Low – moderate |
| Tuvalu | 15:45:40 (Near average or above) | Low – moderate |
| Papua New Guinea | 20:45:35 (Near average) | Low – moderate |
| Solomon Islands | 20:45:35 (Near average) | Low – moderate |
| Vanuatu | 25:45:30 (Near average) | Low – moderate |
| New Caledonia | 35:35:30 (Near average/climatology) | Low |
| Wallis & Futuna | 20:45:35 (Near average) | Low – moderate |
| Tokelau | 30:45:25 (Near average) | Low – moderate |
| Samoa | 25:45:30 (Near average) | Low – moderate |
| Northern Cook Islands | 25:45:30 (Near average) | Moderate |
| Tonga | 25:50:25 (Near average) | Low – moderate |
| Niue | 25:45:30 (Near average) | Low – moderate |
| Southern Cook Islands | 25:50:25 (Near average) | Low – moderate |
| Society Islands | 20:50:30 (Near average) | Moderate |
| Austral Islands | 25:55:20 (Near average) | Moderate |
| Tuamotu Island | 25:55:20 (Near average) | Moderate |
| Pitcairn Island | 20:50:30 (Near average) | Moderate |
| Fiji | 40:40:20 (Near average or below) | Low – moderate |
| Marquesas Islands | 40:45:15 (Near average or 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.