Rainfall outlook for June to August 2004
Above average rainfall in Papua New Guinea and the Austral Islands
Average or below average just west and northeast of the Date Line
Enhanced convection is expected in the equatorial west Pacific over Papua New Guinea, the Solomon Islands and Western Kiribati where rainfall is likely to be average or above average.
Another region of enhanced convection, with average or above average rainfall, is expected over French Polynesia
Rainfall is expected to be average or below average over Vanuati, Fiji, Tuvalu, Tokelau, Samoa and Eastern Kiribati. The skill level of seasonal rainfall forecast is generally between low to moderate during this time of the year.
Rainfall outlook map for June to August 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 | |
|---|---|---|---|
| Papua New Guinea | 20:30:50 | (Above average) | Moderate |
| Austral Islands | 15:35:50 | (Above average) | Low – Moderate |
| Solomon Islands | 15:40:45 | (Average or above) | Moderate |
| Western Kiribati | 15:40:45 | (Average or above) | Moderate |
| Southern Cook Islands | 25:40:35 | (Average or above) | Moderate |
| Society Islands | 20:40:40 | (Average or above) | Moderate |
| Tuamotu Islands | 20:45:35 | (Average or above) | Moderate |
| New Caledonia | 30:45:25 | (Near average) | Moderate |
| Wallis and Futuna | 30:40:30 | (Near average) | Moderate |
| Tonga | 25:45:30 | (Near average) | Moderate |
| Niue | 30:45:25 | (Near average) | Moderate |
| Northern Cook Islands | 25:50:25 | (Near average) | Moderate |
| Pitcairn Island | 25:40:30 | (Near average) | Low – Moderate |
| Marquesas | 20:50:30 | (Near average) | Moderate |
| Eastern Kiribati | 35:40:25 | (Average or below) | Moderate |
| Vanuatu | 40:45:15 | (Average or below) | Moderate |
| Tuvalu | 35:40:25 | (Average or below) | Moderate |
| Tokelau | 35:40:25 | (Average or below) | Moderate |
| Fiji | 35:40:25 | (Average or below) | Low – Moderate |
| Samoa | 45:35:20 | (Average or 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.