Island Climate Update 68 - May 2006

Update on Pacific Islands rainfall outlook
S Burgess, NIWA
Figure 1. Frequency of correct 3-month rainfall outlooks. A score of 100 would mean that all were correct.
Figure 2. Validation scores for 64 (3-month) rainfall outlooks. This chart shows the percentage of correct forecasts. Scores of 60% or more indicate significantly better outcomes than chance.
Figure 3. ICU rainfall forecast skill, by month. Forecasts issued in February, June, and July have the highest skill.
There have now been more than 60 seasonal rainfall outlooks issued for the Southwest Pacific through the ICU.

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 68 – May 2006
April’s climate
Double Inter-Tropical Convergence Zone (ITCZ) in April; South Pacific Convergence Zone (SPCZ) much further southwest than average
Suppressed convection over Nauru, Western and Eastern Kiribati, Tuvalu, and from Vanuatu to Pitcairn Island
Rainfall above average in Niue
Much warmer than average in parts of New Caledonia and Tonga
Eight tropical cyclones so far

Climate developments in April 2006
Outgoing Long-wave Radiation anomalies for April 2006. (Click for enlargement and detail)
The "double ITCZ" structure, usually seen only in La Niña conditions, persisted in April. One region lay north of the equator from the area north of Papua New Guinea extending east across much of the Pacific. Another region extended east, south of the equator, from about Tokelau towards the Marquesas Islands. The SPCZ was displaced much further southwest than average, extending from the Coral Sea southeast toward New Caledonia.

Tropical rainfall outlook: May to July 2006.
Rainfall outlook map for May to July 2006. (Click for enlargement)
Although equatorial SSTs have returned to a neutral ENSO state, there is a lag in atmospheric conditions and rainfall in the southwest Pacific region still depicts La Niña like patterns.
Enhanced convection is expected over Niue and the Southern Cook Islands, where rainfall is expected to be above average.

Tropical pacific rainfall - April 2006
Territory and station name
April 2006 rainfall
total (mm)
April 2006 percent
of average
Australia
Cairns Airport
644.8
339
Townsville Airport
204.6
330
Brisbane Airport
15.2
17
Sydney Airport
10.6
11
Cook Islands
Penrhyn
219.2
108
Rarotonga EWS
170.4
81
Fiji
Rotuma
93.0
32
Udu Point
370.6
134
Nadi
114.2
71
Nausori
264.2
74
Ono-I-Lau
196.8
125
French Polynesia
Hiva Hoa, Atuona
189.4
109
Tahiti – Faa’a
229.2
199
Tuamotu, Takaroa
40.6
34
Gambier, Rikitea
192.6
128
Tubuai
125.8
69
Rapa

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