Guam/CNMI:  The 2007 annual rainfall on Guam was slightly drier than normal, with very dry conditions in the first half of 2007 balanced by abundant rainfall in the 4th Quarter. Annual totals ranged from 83.15 inches at Andersen AFB to 90.50 inches at the head of the Ugum watershed in the southern mountains. While the heaviest rains normally fall during August or September, October was the wettest month of the year for several locations. With no unusually heavy rains or strong winds, the weather on Guam during 2007 is best described as tranquil. The highest daily rainfall at the WSO was 3.92 inches in early August, compared to daily rainfall in excess of 4 inches on seven occasions in 2004, and 4 - 6 inches of rain in one hour during the passage of both typhoons Chataan and Pongsona in 2002! The year’s highest wind gust of 54 mph occurred on July 9th, when Tropical Storm Man-Yi passed to the southwest of the island.

The 2007 annual rainfall totals in the CNMI were generally near normal. As on Guam, most stations received their highest monthly rainfall in October. The island of Rota had a particularly wet October, with 24.89 inches recorded at the Rota Airport and 20.12 inches at the UOG rain gage cluster located at the nearby Rota Resort and Country Club. This rain gage network indicated a peak daily total of 4.26 inches on October 17th, which is not atypical for the wettest day during the annual rainy season on Guam and in the CNMI. (For comparison, the UOG rain gage network at the RRCC measured 4.26 inches of rain in one hour during the passage of Typhoon Chaba close to Rota in August 2004.) The weather was otherwise very tranquil throughout the CNMI during 2007, with no unusually heavy rains or strong winds.

Guam and CNMI Rainfall Summary 4th Quarter 2007

Climate Outlook: The dry season on Guam and in the CNMI is underway. Trade winds have been quite strong, with continual high surf on north and east shores. This type of weather is expected to continue through March. All computer models available to the PEAC Center indicate that the rainfall will be above normal in Guam and the CNMI for the next three months. Similar years have yielded above-average rainfall for Guam and the CNMI. Above normal rains should prevail in the region for most months of the year, although extraordinary rainfall (which is usually associated with typhoons) is not anticipated. The trade winds and sub-surface ocean heating in the western North Pacific will keep sea levels above normal.

Tropical cyclone activity is anticipated to be near normal in Micronesia during 2008. From August through December 2008, Guam and the CNMI may expect to be threatened by 2 or 3 tropical cyclones that will produces gales and hazardous seas in the island waters. The odds of damaging winds (60 mph or higher) from a typhoon on Guam and for each island of the CNMI will be approximately 10 to 15% for all of 2008, which is the normal level of risk for a non-El Niño year.

Forecast rainfall for Guam and the CNMI from February 2008 through January 2009 is as follows:

source: UOG-WERI