Pacific ENSO Update

4th Quarter, 2005 Vol. 11 No. 4

American Samoa:  Now in its dry season, the total rainfall of 33.42 inches in American Samoa during the 3rd Quarter of 2005 was substantially wetter than normal (171%) with most of the rainfall occurring in August and September. July rainfall was near to below normal (95% of normal) to below normal (55% of normal). August and September rainfall was significantly above normal with rainfall at Pago Pago airport approximately double the normal amount (211% and 196% respectively). During September, heavy rains caused significant small stream flooding and a few landslides across Tutuila. Overall, rainfall has been above normal for the first nine months of 2005 (140% of normal).

American Samoa Rainfall Summary 3rd Quarter 2005
Station   Jul. Aug. Sep. Total
Pago Pago WSO Rainfall (inches) 5.43 13.56 14.43 33.42
% of Normal 94% 211% 196% 171%
Aafasou Rainfall (inches) 6.35 20.95 22.00 49.30
% of Normal 55% 167% 157% 126%

Climate Outlook:
The tropical cyclone threat for the 2005/2006 tropical cyclone season is expected to be near normal. According to NIWA’s Island Climate Update, normal for Samoa is one to two tropical cyclones passing within 300 nm of Samoa/American Samoa over the November through May period (http://www.niwascience.co.nz/ncc/icu/2005-10/article).

Despite a long run of above normal rainfall at American Samoa, computer forecasts and a consensus of outlooks from several regional meteorological centers suggest rainfall in American Samoa will be near normal through the upcoming rainy season. Long-range computer rainfall forecasts, however, have only limited skill in the tropical Pacific islands.

Predicted rainfall for American Samoa from November 2005 through October 2006 is:

Inclusive Period
% of Long-Term Average
Nov - Dec 2005 (Onset of Rainy Season)
110%

Jan 2006 - Apr 2006 (Heart of Next Rainy Season)
100%
May - Oct 2006 (Next Dry Season)
100%
source: UOG-WERI