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Three-month outlook

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.