Rainfall outlook for September to November 2003
Normal or above normal rainfall is expected in Papua New Guinea and the Austral Islands Normal or below normal rainfall in the equatorial region and Tuvalu, Fiji, and the Tuamotu and Marquesas Islands
Neutral ENSO conditions suggest a near normal rainfall pattern over many countries in the region. However, enhanced convection is likely over Papua New-Guinea and in the Austral Islands where rainfall is expected to be normal or above normal for the three month forecast period.
Suppressed convection is expected to continue in the equatorial region of Western and Eastern Kiribati resulting in normal or below normal rainfall. Rainfall is also expected to be normal or below normal in Tuvalu, Fiji, and the Tuamotu and Marquesas Islands.
Near normal rainfall is likely elsewhere in the region.
The skill of most of the forecast models is moderate to low for this time of the year as the region transits from the dry to the wet season.
Rainfall outlook map for September to November 2003
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, rainfall is equally likely (33% chance) in any tercile.
The probabilities shown express the expected shift in the distribution from normal, 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 | |
|---|---|---|---|
| Papua New Guinea | 15:45:40 | (Normal or above normal) | Moderate |
| Austral Islands | 20:40:40 | (Normal or above normal) | Low |
| Solomon Islands | 20:50:30 | (Near normal) | Moderate – Low |
| Vanuatu | 25:50:25 | (Near normal) | Moderate – Low |
| New Caledonia | 35:40:25 | (Near normal) | Moderate – Low |
| Wallis and Futuna | 20:50:30 | (Near normal) | Moderate – Low |
| Tonga | 25:50:25 | (Near normal) | Moderate – Low |
| Niue | 25:50:25 | (Near normal) | Moderate – Low |
| Tokelau | 25:50:25 | (Near normal) | Low |
| Samoa | 20:50:30 | (Near normal) | Low |
| Northern Cook Islands | 25:50:25 | (Near normal) | Low |
| Southern Cook Islands | 20:50:30 | (Near normal) | Moderate – Low |
| Society Islands | 15:50:35 | (Near normal) | Low |
| Pitcairn Island | 25:45:30 | (Near normal) | Moderate – Low |
| Eastern Kiribati | 40:40:20 | (Normal or below normal) | Low |
| Western kiribati | 40:40:20 | (Normal or below normal) | Low |
| Tuvalu | 35:40:25 | (Normal or below normal) | Moderate – Low |
| Fiji | 40:40:20 | (Normal or below normal) | Moderate – Low |
| Tuamotu Islands | 40:50:10 | (Normal or below normal) | Moderate – Low |
| Marquesas Islands | 35:40:25 | (Normal or below normal) | 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.