Rainfall outlook for June to August 2003
Average or above average rainfall is expected from Papua New Guinea to the Solomon Islands Average or below average rainfall in Western and Eastern Kiribati
Recent oceanic and atmospheric changes in the equatorial region suggest that July to September rainfall is likely to be average or above average from Papua New Guinea to Samoa including Tuvalu, Wallis and Futuna and Tokelau.
The cooling of SSTs in the equatorial region just east of the Date Line is likely to result in average or below average rainfall in both Western and Eastern Kiribati over the coming three months.
Rainfall is expected to be near average for the rest of the South Pacific region.
The skill of most of the forecast models is reduced during this time of the year.
Rainfall outlook map for July to September 2003
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 subsurface 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 | 20:40:40 | Average or above average | Moderate |
| Solomon Islands | 20:40:40 | Average or above average | Moderate |
| Tuvalu | 20:40:40 | Average or above average | Moderate – Low |
| Wallis and Futuna | 20:40:40 | Average or above average | Moderate – Low |
| Tokelau | 15:40:45 | Average or above average | Moderate – Low |
| Samoa | 15:45:40 | Average or above average | Moderate – Low |
| Vanuatu | 25:50:25 | Near average | Moderate – Low |
| New Caledonia | 30:40:30 | Near average | Low |
| Fiji | 30:40:30 | Near average | Low |
| Tonga | 20:50:30 | Near average | Low |
| Niue | 20:50:30 | Near average | Low |
| Northern Cook Islands | 10:60:30 | Near average | Moderate – Low |
| Southern Cook Islands | 20:50:30 | Near average | Low |
| Society Islands | 15:50:35 | Near average | Low |
| Austral Islands | 20:50:30 | Near average | Low |
| Tuamotu Islands | 20:50:30 | Near average | Moderate |
| Marquesas Islands | 20:60:20 | Near average | Low |
| Pitcairn Island | 25:50:25 | Near average | Moderate – Low |
| Western Kiribati | 40:45:15 | Average or below average | Moderate – Low |
| Eastern Kiribati | 50:35:15 | Below average | Low |
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.