Island Climate Update 35 - August 2003

23 March 2007 - 2:20pm

Science Centres: Pacific Rim

August

Monthly climate

ENSO & SST

Forecast validation

Three-month outlook

Feature article

Data sources

Feature article
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.

August
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 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 & SST
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.

Monthly climate
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.

Three-month outlook
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.

Data sources
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