Rainfall outlook for April to June 2004
Above average rainfall over the Solomon Islands
Suppressed convection in the equatorial eastern Pacific – Eastern Kiribati, the Marquesas Islands and parts of central French Polynesia
Enhanced convection is expected with above average rainfall over the Solomon Islands and average or above average rainfall in Papua New Guinea and Western Kiribati. Another smaller region of enhanced convection is expected near the Date Line resulting in average or above average rainfall in Tonga and Niue. Below average rainfall is likely over the Marquesas Islands. Suppressed convection is also expected over Eastern Kiribati and the Society and Tuamotu Islands where rainfall is likely to be average or below average. The model forecast skill is generally low to moderate at this time of the year.
Rainfall outlook map for April to June 2004
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 | |
|---|---|---|---|
| Solomon Islands | 20:30:50 | (Above average) | Moderate |
| Papua New Guinea | 20:45:35 | (Average or above) | Low |
| Western Kiribati | 20:40:40 | (Average or above) | Low – Moderate |
| Tonga | 20:40:40 | (Average or above) | Moderate |
| Niue | 20:40:40 | (Average or above) | Moderate |
| Vanuatu | 25:45:30 | (Near average) | Low – Moderate |
| New Caledonia | 30:45:25 | (Near average) | Low – Moderate |
| Tuvalu | 25:50:25 | (Near average) | Moderate |
| Wallis and Futuna | 20:45:35 | (Near average) | Moderate |
| Fiji | 30:45:25 | (Near average) | Low – Moderate |
| Tokelau | 30:45:25 | (Near average) | Moderate |
| Samoa | 20:45:35 | (Near average) | Low – Moderate |
| Northern Cook Islands | 20:50:30 | (Near average) | Moderate |
| Southern Cook Islands | 20:50:30 | (Near average) | Moderate |
| Austral Islands | 30:50:20 | (Near average) | Moderate |
| Pitcairn Island | 30:50:20 | (Near average) | Low – Moderate |
| Eastern Kiribati | 35:40:25 | (Average or below) | Moderate |
| Society Islands | 40:40:20 | (Average or below) | Moderate |
| Tuamotu Islands | 40:40:20 | (Average or below) | Moderate |
| Marquesas | 50:30:20 | (Below) | 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.