Three-month outlook

Rainfall outlook for October to December 2002

Enhanced convection and above average rainfall in Western and Eastern Kiribati with above average or average rainfall in Tuvalu, Tokelau and the Marquesas Islands

Below average or near average rainfall from Papua New Guinea southeast to the Society Islands

Below average rainfall for New Caledonia

The El Niño related region of enhanced convection, presently affecting Western and Eastern Kiribati is expected to persist over the October to December 2002 period, resulting in continued above average rainfall in that region, with average or above average rainfall likely in Tuvalu, Tokelau and the Marquesas Islands. Below average or average rainfall is expected from Papua New Guinea to the Society Islands, including Vanuatu, Fiji and Southern Cook Islands. Below average rainfall is expected for New Caledonia. Near average rainfall is likely elsewhere.

Forecast model skills are generally moderate, with the transition to the southern hemisphere wet season. However, the model skills are high for Kiribati.

Rainfall outlook map for October to December 2002

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.

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.