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Pacific ENSO Update

4th Quarter, 2011 Vol. 17 No. 4


American Samoa Flag American Samoa: American Samoa has now passed through the height of its dry season. It was very dry at Pago Pago during the dry season, with a 3-month 2011 3rd Quarter total rainfall of only 8.08 inches (41% of normal). In the typically wetter location of Aasufou, July and September were dry, but were balanced by a wet August so that the 3-month JJA total rainfall of 41.02 inches ended up near normal (108%). During this past dry season, brush fires were reported on the islands of Ofu and Tutuila. Dry streams were also noted. Dry conditions also extended across other island groups in the region. A joint New Zealand and United States operation provided emergency water supplies to drought-stricken Tokelau. The US Coastguard cutter WALNUT (home ported in Honolulu) met with the New Zealand team in Pago Pago, and from there traveled to Tokelau’s three main atolls to bring supplies of fresh water. New Zealand was also responding to an ongoing water shortage emergency in Tuvalu. Strong trade winds and cooler-than-normal SST likely suppressed rainfall at most locations throughout American Samoa and helped to push the SPCZ to the west.

American Samoa Rainfall Summary 3rd Quarter 2011

Station   Jul. Aug. Sep. 3rd Qtr
Predicted
Pago Pago WSO
Rainfall (inches)
2.31
3.85
1.92
8.08
18.70
% of Normal
37%
57%
29%
41%
95%
A'asufou
Rainfall (inches)
9.60
29.36
2.06
41.02
36.13
% of Normal
84%
234%
15%
108%
95%
Predictions made in 2nd Quarter 2011 Pacifc ENSO Update newsletter.

Climate Outlook: American Samoa has just passed through the heart of its dry season with mostly below-normal rainfall. Rainfall has already increased during October to over 8 inches at Pago Pago, nearing its monthly normal of 10.79 inches. Climate models and simple persistence of current conditions favor a continuation of below-normal rainfall through December, as is typical for this region. However, regional rainfall outlooks for the next three months place American Samoa near a sharp gradient of forecast rainfall, with below-normal rainfall to its north and east and above-normal rainfall to its south and west. La Niña conditions persisting through the first few months of 2012 should favor tropical cyclone activity in the Coral Sea from northeast Australia across to Fiji, with a below normal risk of cyclone development near, or south of American Samoa beginning in late November 2011.

Forecast rainfall for American Samoa from October 2011 through September 2012 is as follows:

Inclusive Period

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

October - December 2011
(Onset of Rainy Season)
85%
(29.40 inches - Pago Pago)
January - March 2011
(Heart of Next Rainy Season)
100%
April - May 2012
(Onset of Next Dry Season)
95%
June - October 2012
(Heart of Next Dry Season)
90%

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

source: UOG-WERI



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Web Master's email: peac@noaa.gov
Page Last Modified: December 09 2011 07:08:46 GMT

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