Island Climate Update 35 - August 2003

ENSO Update
The current atmospheric and oceanic observations show a near neutral El Niño Southern Oscillation (ENSO) state in the tropical Pacific region.
In March 2003, the equatorial Pacific (NINO3 and NINO4) seas surface temperature (SST) started cooling, which also coincided with the weakening of easterly trade winds, four months prior to change in the Southern Oscillation Index (SOI).
During May 2003, there was rapid cooling in the equatorial SSTs, which suggested development of of a cool La Niña event.

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 35 – 6 August 2003
July’s climate: The South Pacific Convergence Zone (SPCZ) was active west of the Date Line. However, there was little activity in the east. Rainfall was well above average over much of New Caledonia and Vanuatu. Some locations in New Caledonia recorded 500 mm for the month, after torrential rainfall totalling about 400 mm fell over a two-day period.

Forecast validation
Forecast period: May to July 2003
Enhanced convection with average or above average rainfall was expected from the Solomon Islands across to Eastern Kiribati, including Tuvalu, Tokelau, and Samoa. Average or above average rainfall was also expected over the Society Islands. Average or below average rainfall was projected from Fiji across to Niue, as well as over the Tuamotu Islands. Below average rainfall was forecast for the Marquesas Islands of northern French Polynesia.

ENSO and Sea Surface Temperatures
Neutral state in the tropical Pacific Ocean continues
Negative SST anomalies in the equatorial region near the South American coast
The Equatorial Pacific atmosphere and ocean have been in a neutral state for the last few months. The short-lived sea surface cooling that developed in the east during May has completely dissipated. The equatorial sea surface temperature (SST) anomalies are weak (but generally positive) right across the Pacific. The NINO3 SST anomaly has risen to +0.4°C in July (from –0.4°C in June). NINO4 rose to +0.7°C.

Climate developments in July 2003
Extremely high rainfall over parts of New Caledonia and Vanuatu
Below average rainfall in many islands from Kiribati to French Polynesia
The SPCZ was active west of the Date Line, extending from east of the Solomon Islands toward southern Tuvalu. However, there was little activity in the east. Enhanced convection occurred over Papua New Guinea. Rainfall was at least 200% of average over much of New Caledonia (some locations recording as much as 500 mm) and parts of Vanuatu.

Rainfall outlook for August to October 2003
Average or above average rainfall is expected from Papua New Guinea to Samoa
Average or below average rainfall from Western Kiribati trending east-southeast to the Marquesas Islands
The SPCZ is expected to be near its normal position, with some enhancement about and west of the Date Line. Above average rainfall is expected from Tuvalu to Tokelau, while Papua New Guniea, the Solomon Islands, the Wallis and Futuna islands and Samoa are expected to experience average or above average rainfall.

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