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Pacific ENSO Update

1st Quarter, 2012 Vol. 18 No. 1


NOTE: Rainfall averages in the following local summaries are based on the 1971-2000 normals. The PEAC Center plans to switch to the 1981-2010 normals with the next issue of the Pacific ENSO Update newsletter. Also, the PEAC Center researchers will make efforts to establish normals for the many outer island sites that do not yet have a 30-year climate record available.

American Samoa Flag American Samoa: For eight of the 12 months of 2011, the rainfall at American Samoa was below normal yielding an annual total of 105.86 inches at WSO Pago Pago, which was 87% of normal. The dry season was much drier than normal with every month from March through September below normal. The 28.56 inches of rainfall at Pago Pago during this 7-month period was only 47% of normal. In the final three months of 2011, near-normal rainfall returned to American Samoa as its 2011-12 rainy season began. With 2011 beginning and ending in La Niña, the SPCZ was shifted to the west and south, taking its band of heavier rain away from American Samoa. A notable weather event of 2011 was the passage of Cyclone Wilma directly over American Samoa at the end of January 2011. Peak measured winds were 50 kts with gusts to 70 kts. Damage was not substantial.

American Samoa Rainfall Summary 4th Quarter 2011

Station   Oct Nov Dec 4th Qtr Annual
Pago Pago WSO
Rainfall (inches)
12.67
15.91
9.61
38.19
105.86
% of Normal
117%
147%
66%
106%
87%
A'asufou
Rainfall (inches)
15.57
21.52
17.16
54.25
179.73
% of Normal
83%
119%
88%
96%
94%

Climate Outlook: American Samoa is now entering the heart of its rainy season. Climate models are indecisive on the rainfall in American Samoa over the next few months, and the outlook is for equal chances of above-normal, normal, or below-normal rainfall. With the current La Niña near its peak and anticipated to fade to ENSO-neutral over the next few months, it is likely that no extremes of rainfall would be experienced and that the northwest monsoon and tropical cyclone activity should remain mostly to the west of the region. Recent flooding across Fiji is an example of La Niña weather patterns. It is difficult to forecast rainfall in American Samoa because it is so close to the line where, to the west the rainfall is above normal and to the east, it is below normal. The next dry season (June - September 2012) is currently anticipated to have near-normal rainfall. The risk of a damaging tropical cyclone is typically below normal during La Niña. For the remainder of the cyclone season (through June 2012) we are cautiously optimistic that there will be no substantial adverse impacts from tropical cyclones in the Samoa region. However, the recent direct hit of Hurricane Wilma on American Samoa in late January 2011 illustrates that the risk of a tropical cyclone in American Samoa is never zero during its cyclone season! Through June 2012, South Pacific tropical cyclones should favor the Coral Sea, and be a threat primarily to the east coast of Australia across to Fiji.

Forecast rainfall for American Samoa from January 2012 through December 2012 is as follows:

Inclusive Period

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

January - March 2012
(Heart of Rainy Season)
100%
(37.31 inches - Pago Pago)
April - June 2012
(Onset of Next Dry Season)
100%
July - September 2012
(Heart of Next Dry Season)
100%
October - December 2012
(Onset of Next Rainy 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
c/o NOAA NWS - Weather Forecast Office Honolulu
2525 Correa Road, suite 250
Honolulu, HI 96822
(808) 956-2324

Web Master's email: peac@noaa.gov
Page Last Modified: March 22 2012 05:05:11 GMT

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