Island Climate Update 31 - April 2003

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 31 – 7 April 2003
March’s climate: The El Niño episode is continuing to weaken. Enhanced convection persisted over Western Kiribati, but it was weaker than in most recent months.

ENSO Update
by Ashmita Gosai, Stuart Burgess, and Dr Jim Salinger, NIWA
The now-decaying El Niño event began to affect the South Pacific climate from about the middle of 2002, after the sea surface temperatures (SSTs) in the tropical and eastern equatorial Pacific warmed to about 1°C above normal.

Forecast validation
Forecast period: January to March 2003
The El Niño related region of enhanced convection over Western and Eastern Kiribati was expected to persist. Above average or average rainfall was also expected in Tuvalu, and across central French Polynesia to Pitcairn Island. A tendency towards below average rainfall was expected for a broad region from New Caledonia east to Niue, including Vanuatu, Fiji and Tonga, and also about the Marquesas Islands of northern French Polynesia.

ENSO and Sea Surface Temperatures
El Niño continues to weaken towards a neutral state
Equatorial Pacific SST anomalies eased further
The El Niño event in the tropical Pacific is nearing its end. Most of the leading El Niño Southern Oscillation (ENSO) models show that the event will weaken to a neutral state by early winter in southern hemisphere.
The NINO3 SST anomaly eased further to +0.4°C in March, and NINO4 remains near +1.0°C. The three month (January–March) means are about +0.7°C and +1.1°C for NINO3 and NINO4, respectively.

Climate developments in March 2003
Enhanced convection persists, but weaker than in most recent months over Western Kiribati
SPCZ further east, from the Cook Islands to the south of Pitcairn
The area of enhanced convection that has predominated over the warmer seas around Western Kiribati since August last year showed signs of weakening in March, with some westward movement to affect Nauru. This is related to the equatorial surface easterlies which strengthened further in March, reaching their highest frequency at Tarawa (92% of observations) since April 2002.

Rainfall outlook for April to June 2003
Above average rainfall in Western and Eastern Kiribati, average or above average rainfall expected in the Solomon Islands, Tokelau and Samoa
Average or below average rainfall in New Caledonia and Fiji and below average rainfall in the Marquesas Islands
Continuing enhanced convection in the equatorial Pacific is expected to result in above average rainfall in Western and Eastern Kiribati.

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