Rainfall outlook for July to September 2002
Above average rainfall in equatorial latitudes from Nauru to Kiribati
Average to above average rainfall for the Solomon Islands, Vanuatu and Tuvalu
Average to below average rainfall in New Caledonia, Fiji, Samoa Tokelaus and Marquesas
Mainly around average rainfall in other areas
In the Western Pacific, the South Pacific Convergence Zone (SPCZ) extended east from Solomon Islands to Tuvalu and was virtually non-exsistent further east during June. The SPCZ lay just north of Solomon Islands and Tuvalu, which is further north than its normal position for June.
Rainfall is forecast to be above average in Western and Eastern Kiribati. Average or above average rainfall is expected in Solomon Islands, Vanuatu and Tuvalu.
Below average or average rainfall has been forecast for New Caledonia, Fiji, Samoa, Tokelau and Marquesas Islands.
Other areas are expected to receive around average rainfall for the upcoming three months.
Rainfall outlook map for July to September 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 | |
|---|---|---|---|
| Western Kiribati | Above | 20:20:60 | High |
| Eastern Kiribati | Above | 20:20:60 | High |
| Solomon Islands | Average – Above | 20:40:40 | Moderate – Low |
| Vanuatu | Average – Above | 20:40:40 | Moderate – Low |
| Austral Islands | Average | 15:50:35 | Moderate – Low |
| Niue | Average | 25:50:25 | Low |
| Northern Cook Islands | Average | 20:60:20 | Moderate – Low |
| Papua New Guinea | Average | 20:60:20 | Moderate – Low |
| Pitcairn Island | Average | 25:50:25 | Moderate – Low |
| Society Islands | Average | 20:50:30 | Moderate – Low |
| Southern Cook Islands | Average | 20:60:20 | Moderate – Low |
| Tonga | Average | 25:50:25 | Low |
| Fiji | Below – Average | 35:45:20 | Low |
| Marquesas | Below – Average | 40:40:20 | Moderate – Low |
| New Caledonia | Below – Average | 35:45:20 | Moderate – Low |
| Samoa | Below – Average | 40:40:20 | Moderate – Low |
| Tokelau | Below – Average | 35:45:20 | Moderate – Low |
| Tuvalu | Below – Average | 35:45:20 | Moderate – Low |
| Wallis & Futuna | Below – Average | 40:40:20 | Moderate – 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.