Guam/CNMI:  The 2008 annual rainfall was below normal throughout Guam and the CNMI, with very few extremes of rainfall noted. Annual rainfall totals on Guam during 2008 ranged from a low of 65.24 inches (66%) at Andersen AFB to a high of 81.30 inches (77%) at an experimental rain gage at a location in the Southern Mountains. The Rota Airport reported the highest 2008 total rainfall among all Guam and CNMI stations with its 2008 total of 88.26 inches (93% of its long-term average). At most locations, September was the wettest month of the year, after which the rainfall during the 4th quarter again fell below normal. The weather on Guam and the CNMI during all of 2007 and 2008 can best be described as tranquil and uneventful. Tropical cyclones remained to the west and north, the monsoon was weak or absent, and dry trade winds dominated for almost the entire time. The tranquility of the weather was in itself somewhat remarkable, in that almost no extremes of wind or rainfall have been observed now for over two years! The WFO Guam has not had over 4 inches of rain in 24 hours since August 2006. The year’s only instance of extreme weather occurred on 11-12 December 2008 when Typhoon Dolphin passed near Guam while it was becoming a tropical storm. The WFO Guam issued tropical storm watches and warnings for Guam and portions of the CNMI, marking the only time during 2008 that tropical cyclone watches or warnings were issued for any Micronesia location. On Guam, about an inch of rain was experienced during the passage of Dolphin, and a peak wind gust of 48 kt (55 mph) was recorded in Apra Harbor.

Guam and CNMI Rainfall Summary 4th Quarter 2008

Climate Outlook: The dry season on Guam and in the CNMI is underway. The return to La Niña conditions will keep trade winds stronger and more persistent than normal; this in turn will reinforce the higher than normal sea-levels already present in the western Pacific, and continue to generate rough seas/surf high in the island waters and exposed shores. Tropical cyclone activity will likely be delayed, and once again shifted to the west, reducing the risk of tropical cyclones on Guam and in the CNMI for at least the first half of 2009. Computer models available to PEAC indicate that the rainfall will be near normal in Guam and in the CNMI through the dry season. If La Niña persists into the spring, the ongoing tranquility of the past two years will likely continue for the foreseeable future.

Predicted rainfall for Guam and the Mariana Islands from January 2009 through December 2009 is as follows:

source: UOG-WERI