Three-month outlook

Rainfall outlook for April to June 2002

Above average rainfall in Kiribati and Vanuatu

Average to below average rainfall from the Solomon Islands to the Marquesas, including the Northern Cook Islands and central French Polynesia

The South Pacific Convergence Zone moved south in March, lying over Fiji, Tonga and the Southern Cook Islands: displaced further to the southwest than usual in areas west of the dateline. Rainfall is projected to be above average in Western and Eastern Kiribati and Vanuatu, and average to above average in New Caledonia, Fiji, Niue and Pitcairn Island. Average to below average rainfall is projected for much of the region from the Solomon Islands east to the Marquesas including the Northern Cooks, and central French Polynesia. Average rainfall is more likely in other areas. Forecast skill for most rainfall outlook models is usually lowest at the onset of the South Pacific dry season.

Rainfall outlook map for April to June 2002

Probabilities of rainfall departures from average

Broad-scale rainfall patterns and anomalies in the southern tropical Pacific area 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 terciles (e.g. 20:30:50) are derived from the interpretation of several global climate models. They correspond to the lowest (driest) one third of the rainfall distribution, the middle one third, and 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.