PEAC CENTER TROPICAL CYCLONE OUTLOOK

Beginning in August and continuing especially from September through the end of the year, the geographical distribution of western North Pacific tropical cyclones should become established in a more typical pattern (not seen for the past two years) with a possible easterly shift of the activity in the late fall. Whereas the tropical cyclone activity was far below normal in Micronesia for both 2007 and 2008, activity should return to normal or even above normal during the remaining months of 2009. Guam and the CNMI should see an increased risk of a typhoon through the remainder of 2009. Islands eastward of Guam including Chuuk, Pohnpei, and the RMI, may be threatened by the gales and heavy rains of a tropical cyclone for the first time in several years. At a minimum, the islands of eastern Micronesia should begin to see more episodic heavy rainfall events associated with tropical disturbances, especially in the fall of 2009. Thereafter, beginning roughly in late November or December, American Samoa’s hurricane season could be more active than normal. See each island’s variability summary for discussions of specific tropical cyclone risk.

In the Central Pacific, El Niño conditions are usually associated with a more active tropical cyclone season as there is a greater chance of late season tropical cyclones developing in the Central Pacific. While a more active season does increase the chance of Hawaii being impacted, El Niño conditions do not necessarily mean that a tropical cyclone will hit the islands. The Central Pacific Hurricane Center (CPHC) is currently forecasting a near normal or below-normal hurricane season for the Hawaiian Islands. CPHC predicts three to five tropical cyclones forming in the Central Pacific during the 2009 hurricane season, which officially begins June 1 and ends Nov. 30. An average season has four or five tropical cyclones (which includes tropical depressions, tropical storms and hurricanes).

The PEAC forecast considers input from two seasonal outlooks for tropical cyclone activity in the western North Pacific basin: (1) The City University of Hong Kong Laboratory for Atmospheric Research, under the direction of Dr. J. C-L. Chan, and, (2) The Benfield Hazard Research Centre Tropical Storm Risk (TSR) Research Group at University College London, UK, led by Dr Adam Lea and Professor Mark Saunders.