Rainfall outlook for November 2003 to January 2004
Enhanced convection in Papua New Guinea, the Solomon Islands and Samoa
Average or above average rainfall in parts of French Polynesia
Average or below average rainfall about the Date Line from Vanuatu to Niue
Below average rainfall in Eastern Kiribati and the Marquesas Islands
Enhanced convection in the equatorial western Pacific is likely to result in average or above average rainfall in areas from Papua New Guinea east to the Solomon Islands and Samoa. Another region of average or above average rainfall is expected over the Society Islands and Tuamotu Islands of French Polynesia.
Suppressed convection around the Date Line in the tropical Pacific is expected to result in average or below average rainfall from Vanuatu southeastwards to Niue, including Fiji and Tonga. Below average rainfall is the most likely outcome for Eastern Kiribati and the Marquesas Islands.
The forecast model skill confidence ranges from low to moderate for this seasonal forecast period as it coincides with the commencement of the wet and tropical cyclone season for the southern hemisphere.
Rainfall outlook map for November 2003 to January 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 | 15:45:40 | (Average or above average) | Moderate |
| Solomon Islands | 20:40:40 | (Average or above average) | Moderate |
| Samoa | 15:45:40 | (Average or above average) | Moderate |
| Society Islands | 20:40:40 | (Average or above average) | Moderate |
| Tuamotu Islands | 20:40:40 | (Average or above average) | Moderate |
| Western Kiribati | 25:50:25 | (Near average) | Low |
| Wallis and Futuna | 25:50:25 | (Near average) | Moderate – Low |
| Tuvalu | 10:60:30 | (Near average) | Low |
| Tokelau | 20:50:30 | (Near average) | Low |
| New Caledonia | 35:40:25 | (Near average) | Moderate |
| Northern Cook Islands | 15:50:35 | (Near average) | Moderate – Low |
| Southern Cook Islands | 30:50:20 | (Near average) | Moderate |
| Austral Islands | 30:40:30 | (Near average) | Moderate – Low |
| Tuamotu Islands | 25:50:25 | (Near average) | Low |
| Pitcairn Island | 20:50:30 | (Near average) | Moderate – Low |
| Vanuatu | 45:40:15 | (Average or below average) | Moderate – Low |
| Fiji | 40:40:20 | (Average or below average) | Moderate |
| Tonga | 50:40:10 | (Average or below average) | Moderate – Low |
| Niue | 40:40:20 | (Average or below average) | Moderate – Low |
| Eastern Kiribati | 50:20:30 | (Below averagel) | Moderate – Low |
| Marquesas Islands | 55:35:10 | (Below average) | 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.