Island Climate Update 32 - May 2003

Feature article

Tropical Cyclone summary for the 2002/03 season
Stuart Burgess and Ashmita Gosai, NIWA
‘Fili’, was the only tropical cyclone to occur in April, bringing gale force winds to parts of Tonga on the 14th. This was the ninth tropical cyclone to occur so far this season, the same as that of an average season (9), and three more than during the previous season (6). January 2003 was the most active month, with 3 occurrences. The 2002/03 tropical cyclone season was the most active since the season of 1998/99 when there were also 9 occurrences (see Figure 1).

Forecast validation

Forecast validation
Forecast period: February to April 2003
Enhanced convection over Western and Eastern Kiribati was expected to persist, extending west to include the Solomon Islands. Above average or average rainfall was also expected from Tuvalu across to the Society Islands of central French Polynesia. Below average rainfall was predicted for New Caledonia, the Marquesas Islands and Pitcairn Island. Average or below average rainfall was expected in many areas from Vanuatu east to the Austral Islands, including Fiji and Tonga.

ENSO & SST

ENSO and Sea Surface Temperatures
Neutral conditions prevail in the tropical Pacific
Negative SST anomalies have developed along the South American coast
The El Niño event in the tropical Pacific has ended as most El Niño Southern Oscillation (ENSO) indicators return to neutral conditions.
The NINO3 SST anomaly was zero in April, and NINO4 has eased back to +0.6°C. The three month (February – April) means are about +0.3°C and +0.9°C for NINO3 and NINO4, respectively.

May

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 32 – 8 May 2003
April’s climate: The El Niño episode is now over, with enhanced equatorial easterlies across the Pacific. The South Pacific Convergence Zone (SPCZ) was displaced further north than average, with enhanced convection and above average rainfall in many areas from Tuvalu to the Society Islands of French Polynesia.

Monthly climate

Climate developments in April 2003
SPCZ further north, from Tuvalu to the Society Islands
Enhanced convection no longer exists over Kiribati
The SPCZ was displaced further north than average, with enhanced convection over parts of Tuvalu, Tokelau, and the Society Islands of French Polynesia. April rainfall was at least 125% of average (and 300 mm or more in places) over much of this region.

Three-month outlook

Rainfall outlook for May to July 2003
Average or above average rainfall is expected in many equatorial regions
Average or below average rainfall in Fiji, Tonga, Niue, and the Tuamotu Islands
Below average rainfall in the Marquesas Islands
The enhanced equatorial convection that was prevalent over last year has now dissipated with the strengthening of the easterly tradewinds across the equatorial Pacific. Average or above average rainfall is the most likely outcome for Western and Eastern Kiribati, the Solomon Islands, Tuvalu, Tokelau and the Society Islands.

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

NIWA