Island Climate Update 25 - October 2002

Relative Influences of the Interdecadal Pacific Oscillation and ENSO on the South Pacific Convergence Zone
J.A. Renwick, M.J. Salinger, A.B. Mullan, C.K. Folland & A. Gosai
Figure 1. The SPCZ and its relationship to the pattern of the IPO.
Figure 2. Mean Nov-Apr reanalysis 10m wind divergence for (a) all 1958-1998, (b) El Niño minus La Niña, (c) positive IPO minus negative IPO.
This summary is based on recent work done by NIWA and the U.K. Met Office Hadley Centre (Folland et al 2002).

Forecast validation
Forecast period: July to September 2002
Rainfall was projected to be above average in Western and Eastern Kiribati, and average or above average in the Solomon Islands, Vanuatu and Tuvalu. A trend towards below average rainfall was expected in New Caledonia, Fiji, Samoa, Tokelau and the Marquesas Islands. Average rainfall was forecast for other areas.
The rainfall outlook was as expected for most countries near and west of the Equator.

ENSO and Sea Surface Temperatures
El Niño may persist into early 2003
Further intensification of central equatorial SST anomalies
Central Pacific SST anomalies intensified further during September, with some areas around Kiribati more than 2.0°C above average, surface water temperatures being at least 30°C. The horseshoe like Pacific SST anomaly pattern has developed slightly since August, but at this stage is still surrounded by average SSTs rather than cooler than average waters.

Enhanced convection persists in teh central equatorial Pacific
A large area of very enhanced convection, although less extensive than in August, persisted in the central equatorial Pacific during September. This was assisted by anomalous surface equatorial westerlies between 160°E and 180°E (occurring in 80% of observations at Tarawa, Western Kiribati; the highest frequency there since the middle of the last El Niño in October 1997).

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 25 – 8 October 2002
September’s Climate: A large area of very enhanced convection, associated with the now well-established El Niño, persists in the central equatorial Pacific. This resulted in enhanced rainfall from Nauru across to Eastern Kiribati, with totals at least 200% of average over much of that region, and more than 1000% of average in some areas.

Rainfall outlook for October to December 2002
Enhanced convection and above average rainfall in Western and Eastern Kiribati with above average or average rainfall in Tuvalu, Tokelau and the Marquesas Islands
Below average or near average rainfall from Papua New Guinea southeast to the Society Islands
Below average rainfall for New Caledonia
The El Niño related region of enhanced convection, presently affecting Western and Eastern Kiribati is expected to persist over the October to December 2002 period, resulting in continued above average rainfall in that region, with average or above

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