Island Climate Update 42 - March 2004

Pacific Island weather and the MJO
Dr Mike Revell, NIWA
The Madden-Julian Oscillation (MJO) is the major mode of variability of the tropical atmosphere-ocean system on time scales of 30 to 70 days. The MJO organizes convection into an eastward-propagating envelope of smaller-scale disturbances. This envelope moves eastward at between 5 and 10 ms-1 on average, generally forming in the tropical Indian Ocean and dissipating over the central Pacific. It is generally most active during the southern hemisphere summer and autumn.

Forecast validation
Forecast period: December 2003 to February 2004
Above average rainfall was expected for Western Kiribati with enhanced convection expected in the equatorial region extending from the Solomon Islands eastwards to Tokelau, Tuvalu and Wallis and Futuna. Below average rainfall was forecast for Eastern Kiribati, with average or below average rainfall in the Marquesas Islands. Rainfall was lower than expected in Tonga, central and southern French Polynesia region.

ENSO and Sea Surface Temperatures
Western Pacific warmer than usual
Average SSTs in NINO4
The equatorial Pacific remains in a neutral state. Equatorial SSTs have eased further, but are slightly higher than normal, especially in the west. The monthly SOI continues to fluctuate, associated with the Madden-Julian Oscillation (MJO). The mean SOI for February was +0.7, and +0.1 for December to February. The NINO3 SST anomaly for February was about +0.2°C and NINO4 about +0.6°C (December to February are +0.5°C and +0.8°C, respectively).

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 42 – 5 March 2004
February’s climate: Tropical cyclone ‘Ivy’, the second this season, brought severe winds and heavy rainfall to parts of Vanuatu on the 25 – 26th of February. The South Pacific Convergence Zone (SPCZ) was located further south than usual in many areas, with above average rainfall over much of Fiji and the Southern Cook Islands.

Climate developments in February 2004
SPCZ was further south than usual
Above average rainfall in parts of Fiji, Vanuatu and the Southern Cook Islands
An extensive region of below average rainfall from Western Kiribati to Pitcairn Island
The Southwest Pacific OLR/rainfall anomaly pattern changed again, withthe February patterns almost opposite that of January. The SPCZ was located further south than usual in many areas, extending east-southeast from the Solomon Islands toward Fiji, across to Samoa, and over the Southern Cook Islands.

Rainfall outlook for March to May 2004
Enhanced convection in Western Kiribati, Vanuatu, the Wallis and Futuna, and the Society Islands
Average or below average rainfall likely over the Tuamotu Islands and Pitcairn Island
Below average rainfall is expected in the Marquesas Islands
Enhanced convection is expected in Western Kiribati, Vanuatu, Wallis and Futuna and the Society Islands, resulting in average or above rainfall around this region.

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