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Tropical rainfall and SST outlook: June to August 2012

The Pacific is currently in an ENSO–neutral state and is forecast to remain so, or transition towards El Niño conditions, over the next three months.

Precipitation anomalies experienced over the past three months are easing off. However rainfall amounts for June–August are still expected to be higher than normal over the Equator, as well as – to a lesser extent – in the southern part of the southwest Pacific, over and South of Tonga.

Lower than normal rainfall could still affect the region extending from Tuvalu to the Society Islands. Near or above normal rainfall is forecast for Western and Eastern Kiribati, Tonga, Niue and Papua New Guinea. Near normal rainfall is expected for the Solomon Islands, Vanuatu, New Caledonia, Fiji, the Southern Cook Islands, the Tuamotu Archipelago, the Marquesas and Pitcairn. Normal or below normal rainfall is expected for Tuvalu, Samoa, Tokelau, the Northern Cook Islands, the Society Islands and Wallis & Futuna.

The global model ensemble shows sea surface temperature signals that indicate the development of El Niño conditions, with warm anomalies in the equatorial region to the east of the Dateline. Normal or below normal SSTs are forecast for Western Kiribati, the Tuamotu Archipelago, the Society Islands, the Northern Cook Islands, Tokealu, and the Marquesas. Above normal SSTs are expected for Fiji, Niue and Tonga. Near normal or above normal sea surface temperatures are forecast for Papua New Guinea, the Solomon Islands, New Caledonia, Vanuatu, the Austral Islands and the Southern Cook Islands. Near normal SSTs are forecast for Eastern Kiribati, Pitcairn Island, Wallis & Futuna, Tuvalu, and Samoa.

The confidence for the rainfall outlook is moderate to high. The average region–wide hit rate for rainfall forecasts issued in June is 63%, equal with the long–term average for all months combined.

The SST forecast confidence is moderate to high across the region, and uncertainty is greatest near the Marquesas and Solomon Islands.

SST anomaly outlook map for June to August 2012
Rainfall and sea surface temperature estimates for Pacific Islands for the next three months are given in the tables below. The tercile probabilities (e.g., 20:30:50) are derived from the averages of several global climate models. They correspond to the odds of the observed rainfall or sea surface temperatures being in the lowest one third of the distribution, the middle one third, or the highest one third of the distribution. For the long term average, it is equally likely (33% chance) that conditions in any of the three terciles will occur. If conditions are climatology, we expect and equal change of the rainfall being in any tercile.