Rainfall outlook for December 2003 to February 2004
Average or above average from Western Kiribati southeast to the Tuamotu Islands
Trending below average in New Caledonia, Eastern Kiribati and the Marquesas Islands
Enhanced convection is expected in the equatorial region just west of the Date Line, resulting in average or above average rainfall from Western Kiribati across to the Tuamotu Islands, including the Solomon Islands, Tuvalu, Tokelau and Wallis and Futuna. Average or below average rainfall is forecast for New Caledonia and the Marquesas Islands. Rainfall is expected to be below average in Eastern Kiribati.
Near average rainfall is likely elsewhere in the region. Seasonal forecast model skills are expected to range from moderate to high for the coming three months as the wet season commences.
Rainfall outlook map for December 2003 to February 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 | |
|---|---|---|---|
| Western Kiribati | 20:40:40 | (Average or Above) | Low |
| Solomon Islands | 10:50:40 | (Average or Above) | Moderate |
| Tuvalu | 20:40:40 | (Average or Above) | Moderate – High |
| Wallis and Futuna | 10:50:40 | (Average or Above) | Moderate – High |
| Tokelau | 10:50:40 | (Average or Above) | Moderate |
| Tuamotu Island | 10:40:50 | (Average or Above) | Moderate |
| Papua New Guinea | 20:50:30 | (Near average) | Moderate |
| Vanuatu | 20:60:20 | (Near average) | Moderate – High |
| Fiji | 30:45:25 | (Near average) | Moderate – High |
| Tonga | 25:60:15 | (Near average) | Moderate – High |
| Niue | 25:60:15 | (Near average) | Moderate – High |
| Samoa | 20:60:20 | (Near average) | Moderate |
| Northern Cook Islands | 25:60:15 | (Near average) | Moderate |
| Southern Cook Islands | 20:50:30 | (Near average) | Moderate – High |
| Society Islands | 20:45:35 | (Near average) | Low |
| Austral Islands | 20:45:35 | (Near average) | Low |
| Pitcairn Island | 15:60:25 | (Near average) | Moderate |
| New Caledonia | 40:40:20 | (Below or Average) | Moderate |
| Marquesas Islands | 50:40:10 | (Below or Average) | Moderate |
| Eastern Kiribati | 50:20:30 | (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.