American Samoa:  Month-to-month variability of rainfall was high during 2008. At Pago Pago, three months received over 15 inches of rainfall (January, May, and December), and four months received less than 5 inches of rain (February, July, August, and October). The 2008 annual total rainfall of 129.66 inches at Pago Pago was 109% of its normal value. No serious impacts were noted from tropical cyclones during 2008. In early January, the northwest monsoon extended across the islands of American Samoa for a few days. During this time, there were devastating floods in Fiji, but most of the monsoonal cloud band remained to the southwest of Samoa. This may be a herald of how the monsoon will behave for the rest of American Samoa’s rainy season.

American Samoa Rainfall Summary 4th Quarter 2008

Climate Outlook: American Samoa is now within the heart of its rainy season (December - April). Nearly all climate models favor near normal to slightly below normal rainfall for at least the next three months. Thereafter, American Samoa enters its typical dry season, and the rainfall should be near normal. Past rainfall in American Samoa during some similar La Niña years has been near normal. With La Niña conditions, tropical cyclone activity tends to remain in the Coral Sea and near Fiji. The northwest monsoon does not extend across American Samoa as frequently during La Niña; instead, heavy monsoonal rainfall remains southwest of Samoa, and its accompanying tropical cyclones and heavy rainfall affect Fiji and islands in the Coral Sea.

The PEAC Center remains cautiously optimistic that the focus of South Pacific tropical cyclone activity will remain in the Coral Sea from northeastern Australia eastward to Fiji (see Tropical Cyclone Outlook). Through April 2009, it is likely that the monsoon will bring two or three prolonged (3- to 5-day) episodes of gusty northwest wind (20-25 kt), with or without the help of a tropical cyclone along the axis of the monsoon trough/South Pacific Convergence Zone (SPCZ). The risk of a damaging impact by a hurricane or strong tropical storm in American Samoa is considered to be slightly below normal (roughly a 5% to 10% chance) through April 2009.

Forecast rainfall for American Samoa from January 2009 through December 2009 is as follows:

source: UOG-WERI