Pacific ENSO Update

2nd Quarter, 2006 Vol. 12 No. 2

American Samoa:  The 1st Quarter 2006 rainfall total of 61.64 inches at Pago Pago WSO and 87.97 inches at Aafasaou was much wetter than normal (168% and 165% respectively); compared to stations throughout Micronesia, it was matched only by the approximately 65 inches of rain at Kosrae locations during the 1st Quarter of 2006. Three tropical cyclones tracked close to Tonga during January and February, and these combined with a very active phase of the Australian Northwest monsoon caused enhanced northwesterly winds in Samoa with abundant rainfall. In March, the eastern end of the Australian Northwest Monsoon retreated to the Coral Sea, which shifted the focus of tropical cyclone activity and monsoonal rains to that area and away from Samoa.

American Samoa Rainfall Summary 1st Quarter 2006
Station   Jan. Feb. Mar. Total
Pago Pago WSO Rainfall (inches) 23.87 29.27 8.50 61.6
% of Normal 190% 229% 75% 168%
Aasufou Rainfall (inches) 32.05 44.90 11.02

87.97

% of Normal 173% 250% 65% 165%

Climate Outlook:
Although American Samoa is nearing the onset of its dry season, computer forecasts and a consensus of outlooks from several regional meteorological centers indicate that rainfall in American Samoa is likely to remain above normal for at least the next three months. Long-range computer rainfall forecasts, however, have only limited skill in the tropical Pacific islands.

One more tropical cyclone may form within the area from Fiji to Samoa in the next two months. Any such cyclone, however, is anticipated to move to the southeast and spare Samoa from any damaging effects. Thus, the threat of a damaging tropical cyclone in any of the islands of American Samoa is essentially over until the next rainy season (2006-07) when a normal distribution of tropical cyclones in the South Pacific region near American Samoa is anticipated. Normal cyclone activity for an entire rainy season indicates that two or three named tropical cyclones would pass to the south of American Samoa producing episodes of heavy rainfall and gale force northwesterly winds.

Inclusive Period
% of Long-Term Average
May-Jun (End of 2006 Rainy Season)
110%
Jul-Sep 2006 (Heart of Next Dry Season)
95%
Oct - Dec 2006 (Onset of next Rainy Season)
100%
Jan -Apr 2007 (Heart of next Rainy Season)
110%
source: UOG-WERI