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Pacific ENSO Update

3rd Quarter, 2011 Vol. 17 No. 3


American Samoa Flag American Samoa: American Samoa has entered the heart of its dry season. After a very wet January and a normally wet February, all the following months have been drier than normal. May was exceptionally dry, especially in the typically wet location of Aasufou, where the 3.41 inches of rain was only 19% of the May average. In fact, it was the driest May recorded there in the station’s 30-year history, easily beating the previous record low amount of 6.47 inches measured there in May 1983. In stark contrast, the 44.14 inches of rainfall at Aasufou during January 2011 was the 2nd wettest January reading. Rainfall at Pago Pago typically exceeds 10 inches per month from October through April, and is less than 10 inches per month from May through September. Its driest month is July, with an average of just over 6 inches. This year, the monthly rainfall at Pago Pago fell below 10 inches in March, and has been dry since then. Thus the 3rd Quarter rainfall at Pago Pago was only 50% of normal.

American Samoa Rainfall Summary 2nd Quarter and 1st Half 2011

Station   April May June 2nd Qtr
1st Half
Pago Pago WSO
Rainfall (inches)
4.01
3.69
7.01
14.71
59.59
% of Normal
33%
37%
95%
50%
90%
A'asufou
Rainfall (inches)
5.37
3.41
13.14
21.92
84.46
% of Normal
30%
19%
103%
40%
81%

Climate Outlook: American Samoa is now in the heart of its dry season. Conditions during the start of the current dry season were much drier than normal. Climate models and simple persistence of current conditions favor a continuation of below normal rainfall over the next three-month period. The next rainy season (Oct 2011- Apr 2012) is anticipated to have a normal onset with near average rainfall. ENSO-neutral conditions persisting through the latter half of 2011 should favor tropical cyclone activity in the Coral Sea from northeast Australia across to Fiji, with a near normal risk of tropical cyclone development near, or south of, American Samoa beginning in late November 2011.

Forecast rainfall for American Samoa from July 2011 through June 2012 is as follows:

Inclusive Period

% of Long-Term Average Rainfall /
Forecast Rainfall (inches)

July - September 2011
(Heart of Dry Season)
85%
(14.84 inches - Pago Pago)
October - December 2011
(Onset of Next Rainy Season)
95%
January - March 2012
(Heart of Next Rainy Season)
100%
April - June 2012
(Onset of Next Dry Season)
100%

Forecast rainfall quantities represent BEST ESTIMATES given the probabalistic forecast for each particular season and station.

source: UOG-WERI



Pacific ENSO Applications Climate (PEAC) Center
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Web Master's email: peac@noaa.gov
Page Last Modified: August 09 2011 02:01:41 GMT

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