Island Climate Update 33 - June 2003

Update on pacific island rainfall outlooks
Stuart Burgess, NIWA
More than 30 rainfall outlooks for the Southwest Pacific have been issued through the ICU, so we now have enough information to accurately assess how the forecasts have been faring over the past few years. Figure 1 indicates how often the forecasts have been correct, in a categorical sense.

Forecast validation
Forecast period: March to May 2003
Enhanced convection was expected over Western and Eastern Kiribati, possibly extending south to include Tuvalu. Below average rainfall was expected in the Marquesas Islands of northern French Polynesia, with average or below average rainfall in most areas from New Caledonia to the Austral Islands, including Fiji, Tonga, Samoa and Niue.

ENSO and Sea Surface Temperatures
Transition to La Niña like conditions in the equatorial Pacific
Negative SST anomalies (-2°C) along the South American coast
Sea surface temperature (SST) conditions in the equatorial Pacific indicate a rapid shift towards a La Niña like pattern. These conditions are likely to last through the southern hemisphere winter.
The NINO3 SST anomaly was -0.4°C in May, and NINO4 has eased back to +0.3°C. The three month (March – May) means are about -0.1°C and +0.6°C for NINO3 and NINO4, respectively.

An overview of the present climate in the tropical South Pacific Islands, with an outlook for the coming months, to assist in dissemination of climate information in the Pacific region.
Number 33 – 10 June 2003
May’s climate: The South Pacific Convergence Zone (SPCZ) was displaced further east than average, with enhanced convection and above average rainfall over Samoa and the Northern Cook Islands, and the Tuamotu Islands of French Polynesia. Rainfall totals were also above average in parts of Vanuatu and New Caledonia.

Climate developments in May 2003
SPCZ further east, from Samoa to the Tuamotu Islands
Reduced convection along the equator
The SPCZ was displaced further east than average, with enhanced convection over Samoa and the Northern Cook Islands, and the Tuamotu Islands of French Polynesia. May rainfall was at least 125% of average (totalling 200-300 mm at most locations) throughout much of this region.
Rainfall totals were also 125% or more of average in parts of Vanuatu and New Caledonia.

Rainfall outlook for June to August 2003
Average or above average rainfall is expected from Papua New Guinea to the Solomon Islands, also from Wallis and Futuna to the Society Islands
Average or below average rainfall in the Marquesas Islands
Based on the recent climatic transitions in the equatorial Pacific, rainfall is expected to be average or above average from Papua New Guinea to the Solomon Islands, and also from Wallis and Futuna across to the Northern Cook Islands and Society Islands, including Samoa and Tokelau.
Average or below average rainfall is likely in the Marquesas Islands.

Sources of South Pacific rainfall data
This bulletin is a multi-national project with important collaboration from the following Pacific nations:
American Samoa
Australia
Cook Islands
Fiji
French Polynesia
Kiribati
New Caledonia
New Zealand
Niue
Papua New Guinea
Pitcairn Island
Samoa
Solomon Islands
Tokelau
Tonga
Tuvalu
Vanuatu
Requests for Pacific island climate data should be directed to the Meteorological Services concerned.
Acknowledgements
This bulletin is made possible with financial support from the New Zealand Agency for International Development (NZAID), Wellington, New Zealand, wi