Pacific ENSO Update

1st Quarter, 2006 Vol. 12 No. 1

American Samoa:  Overall, rainfall in American Samoa was above average for 2005. Pago Pago WSO recorded 146.23 inches (120%) for the year, and Aafasou recorded 256.53 inches (133%). Only a few locations in the USAPI had rainfall that was more than 120% of the annual normal. Abundant rainfall in June, August, and September (normally the dry season) accounted for much of the surplus. The year ended with a very wet December where 21.03 inches (145%) at Pago Pago and 29.20 inches (150%) at Aafasou.

American Samoa Rainfall Summary 4th Quarter 2005
Station   Oct. Nov. Dec. Total Annual
Pago Pago WSO Rainfall (inches)
6.75
9.69
21.03
37.47
146.23
% of Normal
63%
89%
145%
104%
120%
Aafasou Rainfall (inches)
13.22
23.89
29.2
66.31
256.53
% of Normal
70%
132%
150%
118%
133%

Climate Outlook:
Computer forecasts and a consensus of outlooks from several regional meteorological centers indicate that rainfall in American Samoa is likely to be slightly above normal through the current rainy season. Long-range computer rainfall forecasts, however, have only limited skill in the tropical Pacific islands.

The threat of a tropical cyclone in the islands of American Samoa is expected to be near normal. According to NIWA’s Climate Update normal distribution of tropical cyclones in the South Pacific region near American Samoa indicates that one to two tropical cyclones should pass within 300 nm of American Samoa <http://www.niwascience.co.nz/ncc/icu/2005-10/article>. These cyclones would produce episodes of heavy rainfall and gale force northwesterly winds. A direct strike by an intense hurricane such as occurred during February 2005 is not expected.

Predicted rainfall for American Samoa from January 2005 through December 2006 is:

Inclusive Period
% of Long-Term Average
Jan - May 2006 (Heart of 2006 Rainy Season)
110%
Jun - Sep 2006 (Next Dry Season)
95%
Oct – Dec 2006 (Onset of next Rainy Season)
110%
source: UOG-WERI