Tropical rainfall outlook: January to March 2005
The tropical Pacific Ocean is still in a weak El Niño state and this will continue to influence rainfall patterns in the Pacific region over the next three months.
Enhanced convection is expected in the equatorial region of Western and Eastern Kiribati and Tuvalu where rainfall is forecast to be above average. Rainfall is likely to be near or above average in Tokelau, the Northern Cook Islands, and the Society Islands of French Polynesia.
Suppressed convection is expected over New Caledonia and the Marquesas Islands, where rainfall is likely to be below average.
The region of near or below average rainfall is expected to be exceptionally large for the coming three months from Papua New Guinea extending east southeast to the Southern Cook Islands, including Vanuatu, Fiji, Tonga, Niue, and Samoa.
Near average rainfall is likely for the rest of the forecast region.
Rainfall outlook map for January to March 2005
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 | Outlook confidence |
---|---|---|
Western Kiribati | 20:20:60 (Above) | High |
Eastern Kiribati | 20:30:50 (Above) | Moderate – high |
Tuvalu | 20:30:50 (Above) | Moderate – high |
Tokelau | 15:40:45 (Near average or above) | Moderate – high |
Northern Cook Islands | 15:45:40 (Near average or above) | Moderate |
Society Islands | 15:45:40 (Near average or above) | Moderate |
Solomon Islands | 35:45:20 (Near average) | Low – Moderate |
Wallis and Futuna | 35:45:10 (Near average) | Moderate |
Austral Islands | 30:50:20 (Near average) | Moderate |
Tuamotu Islands | 20:45:35 (Near average) | Moderate |
Pitcairn Island | 30:50:20 (Near average) | Moderate |
Papua New Guinea | 40:40:20 (Near average or below) | Moderate |
Vanuatu | 40:45:15 (Near average or below) | Moderate |
Fiji | 40:45:15 (Near average or below) | Moderate |
Tonga | 40:45:15 (Near average or below) | Moderate |
Niue | 40:40:20 (Near average or below) | Moderate |
Samoa | 40:45:15 (Near average or below) | Low – moderate |
Southern Cook Islands | 40:45:15 (Near average or below) | Low – moderate |
New Caledonia | 50:35:15 (Below) | Moderate |
Marquesas Islands | 50:30:20 (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.