Rainfall outlook for May to July 2004
Enhanced convection over the Solomon Islands
Suppressed convection over the Marquesas Islands
Enhanced convection is expected just west of the Date Line over the region of the Solomon Islands where rainfall is forecast to be above average. Average or above rainfall is likely over Western and Eastern Kiribati, Samoa, the Northern Cook Islands, the Society Islands and the Austral Islands.Average or below average rainfall is expected over Tuvalu and the Tokelau Islands. Suppressed convection over the Marquesas Islands is likely to result in below average rainfall there.
Near average rainfall is expected elsewhere in the region. The forecast model skills are generally moderate to low during this time of the year.
Rainfall outlook map for May to July 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 | 20:35:45 | (Above average) | Moderate – High |
| Western Kiribati | 25:40:35 | (Average or above) | Moderate |
| Eastern Kiribati | 25:40:35 | (Average or above) | Low – Moderate |
| Samoa | 20:40:40 | (Average or above) | Low – Moderate |
| Northern Cook Islands | 15:40:45 | (Average or above) | Low – Moderate |
| Society Islands | 20:40:40 | (Average or above) | Moderate |
| Austral Islands | 30:30:40 | (Average or above) | Moderate |
| Papua New Guinea | 15:55:30 | (Near average) | Moderate |
| New Caledonia | 35:45:20 | (Near average) | Low – Moderate |
| Vanuatu | 30:45:25 | (Near average) | Low – Moderate |
| Wallis and Futuna | 20:50:30 | (Near average) | Low – Moderate |
| Fiji | 30:45:25 | (Near average) | Low – Moderate |
| Tonga | 20:45:35 | (Near average) | Moderate |
| Niue | 20:45:35 | (Near average) | Moderate |
| Southern Cook Islands | 30:40:30 | (Near average) | Low |
| Tuamotu Islands | 30:40:30 | (Near average) | Moderate |
| Pitcairn Island | 30:50:20 | (Near average) | Moderate |
| Tuvalu | 35:40:25 | (Average or below) | Moderate |
| Tokelau | 40:35:25 | (Average or below) | Moderate |
| Marquesas | 55:30:15 | (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.