Island Climate Update 49 - October 2004

ENSO Update
Current oceanic observations show El Niño/Southern Oscillation (ENSO) characteristics in the tropical Pacific region which are not coupled with the atmosphere
In July 2004, the tropical Pacific showed mixed warming and cooling signals, and Southern Oscillation Index (SOI) fluctuations occurred from April 2004. The equatorial sea surface temperature (SST) anomalies were below average near the South American coast but above average over the remainder of the equatorial tropical Pacific east of the Date Line. These were more than 1°C above average near the Date Line.

Forecast validation
Forecast period: October to December 2004
Above average rainfall was expected in the Austral Islands, with average or above average rainfall in Samoa, Niue, the Southern Cook Islands, and the Society Islands. Enhanced convection with average or above average rainfall was also expected over Western and Eastern Kiribati and Tuvalu.

ENSO and Sea Surface Temperatures
Despite the equatorial Pacific sea surface and subsurface temperatures being in an El Niño state, the atmosphere is yet to respond to the oceanic signals. The Southern Oscillation Index (SOI) weakened during September to -0.4, with the three month mean (July to September) at -0.7. Equatorial sea surface temperature (SST) anomalies rose compared to August. The NINO3 average anomaly was +0.9°C (August was +0.6°C) and July to September mean was +0.6°C.

Climate developments in September 2004
The South Pacific Convergence Zone (SPCZ) extended from Papua New Guinea south-southeast to Rotuma Island. Convergence also occurred south of Fiji east to the Southern Cook Islands, including Tonga, some areas recording at least 200% of average rainfall. The enhanced rainfall over Papua New Guinea and the Solomon Islands was caused by cross-equatorial northerlies converging with the southern hemisphere trade winds.

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 49 – October 2004
September’s climate: The South Pacific Convergence Zone (SPCZ) extended from Papua New Guinea to Rotuma Island (Fiji). Convergence also occurred south of Fiji east to the Southern Cook Islands. High rainfall persisted throughout much of Tonga. Below average rainfall occurred in Vanuatu, New Caledonia, central and southern French Polynesia and Pitcairn Island.

Tropical rainfall outlook: October to December 2004
The current incoherent El Niño/Southern Oscillation (ENSO) state in the equatorial Pacific is expected to influence rainfall to some extent across the region for the coming three months.
Enhanced convection is expected in the Enhanced equatorial region of Western and Eastern Kiribati, where rainfall is likely to be above Kiribati, where rainfall is likely to be above average. Near or above average rainfall is expected from the Solomon Islands trending eastwards to Tokelau including Tuvalu.

Tropical pacific rainfall - September 2004
Territory and station name
September 2004 rainfall total (mm)
Long-term average (mm)
September 2004 percent of average
Lowest on record (mm)
Highest on record (mm)
Records began
Australia
Cairns Airport
6.4
36
18
0
103
1941
Townsville Airport
6.2
11
56
0
81
1940
Brisbane Airport
31.0
35
89
0
104
1929
Sydney Airport
79.4
63
126
2
249
1929
Cook Islands
Rarotonga Airport
288.7
109
265
13
268
1929
Fiji
Rotuma
324.7
238
136
48
899
1912
Nadi
72.2
70
103
0
279
1942
Nausori
146.8
165
89
12
473
195

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