Rainfall outlook for August to October 2002
Above average or average rainfall in equatorial latitudes from west to east and Pitcairn Island
Below average or near average rainfall from Papua New Guinea to New Caledonia across to the Southern Cook Islands
Mainly average rainfall in other areas
The SPCZ extended east from the south of Tuvalu to the east of Samoa in August, but it continued to be weak with little activity further east in the Southwest Pacific.
Rainfall is projected to be above average in Western and Eastern Kiribati, while Tuvalu, Tokelau, Wallis & Futuna and Pitcairn Island are likely to receive above average or average rainfall for September to November period. Confidence is high throughout Kiribati as above average rainfall is usually well correlated to negative SOI indices at this time of year and almost all global climate models are predicting above average rainfall there.
Below average or average rainfall is expected in a broad region from Papua New Guinea southeast to New Caledonia, across to Tonga and the Southern Cook Islands. Average rainfall is expected elsewhere.
Confidence levels are lower for model skills at most stations south of 10°;S as the dry to wet season transition takes place.
Rainfall outlook map for September to November 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.
| Island Group | Rainfall Outlook | Confidence in the Outlook | |
|---|---|---|---|
| Western Kiribati | 15:25:60 | (Above) | High |
| Eastern Kiribati | 15:25:60 | (Above) | High |
| Wallis & Futuna | 15:35:50 | (Average or above average) | Moderate – High |
| Tuvalu | 10:40:50 | (Average or above average) | Moderate – High |
| Tokelau | 10:40:50 | (Average or above average) | Moderate |
| Pitcairn Island | 20:35:45 | (Average or above average) | Moderate |
| Solomon Islands | 30:45:25 | (Near average) | Moderate |
| Vanuatu | 25:50:25 | (Near average) | Moderate |
| Fiji | 30:40:30 | (Near average) | Moderate |
| Samoa | 30:50:20 | (Near average) | Moderate |
| Northern Cook Islands | 20:50:30 | (Near average) | Moderate |
| Society Islands | 30:55:15 | (Near average) | Moderate |
| Austral Island | 35:50:15 | ( Near average) | Moderate |
| Papua New Guinea | 40:35:25 | (Average or below average) | Moderate |
| New Caledonia | 50:40:10 | (Average or below average) | Moderate |
| Tonga | 40:40:20 | (Average or below average) | Moderate |
| Niue | 40:45:15 | (Average or below average) | Moderate |
| Southern Cook Islands | 40:50:10 | (Average or below average) | Moderate |
| Marquesas Islands | 45:40:15 | (Average or below average) | Low |
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.