Island Climate Update 53 - February 2005

The Southwest Pacific Climate in 2004
Stuart Burgess & Dr Jim Salinger, NIWA
In 2004, the El Niño/Southern Oscillation (ENSO) conditions evolved from a neutral state in the first half of the year to a weak El Niño event in the central equatorial Pacific in the second half of the year (Figure 1). The trade winds were near normal in strength at the start of the year, but equatorial westerly wind bursts occurred, often reaching the Date Line, from June onwards.

Forecast validation
Forecast period: November 2004 to January 2005
Enhanced convection and above average rainfall were expected over Eastern and Western Kiribati and Tuvalu, with average or above average rainfall over Tokelau and the Northern Cook Islands. Suppressed convection and below or average rainfall was expected over Papua New Guinea southeast to the Southern Cook Islands, including Fiji, Tonga, and Niue. Average or below average rainfall was forecast for the Marquesas Islands.

ENSO and Sea Surface Temperatures
During January, El Niño/Southern Oscillation (ENSO) conditions in the tropical Pacific eased. The Southern Oscillation Index (SOI) rose to near zero in January, weakening the three-month November to January mean to -0.7. The NINO3.4 average anomaly was about +0.7 °C in January, slightly lower than in December. Subsurface temperature anomalies remained positive (between +1 and +2 °C) in the top 100 m across much of the Equatorial Pacific.

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 53 – February 2005
January’s climate: South Pacific Convergence Zone extended from Papua New Guinea southeast to Tokelau. Enhanced convergence in the west, suppressed convection in the east. Warmer than usual temperatures throughout much of the Southwest Pacific.

Climate developments in January 2005
Unlike in December 2004, the South Pacific Convergence Zone (SPCZ) was quite active west of the Date Line, extending from Papua New Guinea east toward Tokelau. This was linked to a large region of enhanced convergence, which also affected the Caroline Islands, the Solomon Islands, and Vanuatu. Enhanced convergence also affected New Caledonia, with generally well above average rainfall there, some places recording more than 600 mm (mainly from the passage of tropical cyclone Kerry near Chesterfield Island to the west over 8-13 January).

Tropical rainfall outlook: February to April 2005
Enhanced convection is forecast in the equatorial region of Western and Eastern Kiribati and Tokelau, where rainfall is expected to be above average. Above average or near average rainfall is forecast for Tuvalu, Northern Cook Islands, Austral Islands, and Pitcairn Island.
Suppressed convection is likely over the Solomon Islands, Vanuatu, New Caledonia, Fiji and Samoa, where rainfall is expected to be near average or below average.

Tropical Cyclone Update
Tropical cyclone 'Lola' affected the region near Tonga from 31 January to 2 February, with maximum sustained winds speeds of 63 km/h. Surface pressures fell to 998 hPa at Fua'amotu Airport, with a period of strong winds there on 1 February. Tropical cyclone 'Meena', the 4th named occurrence this season, was east of Samoa on 3 February, and tracking towards the Southern Cook Islands at the time of writing. So far, central pressures have been below 970 hPa with estimated maximum sustained wind speeds of 230 km/h.

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