Guam/CNMI:  Overall, the 3rd Quarter of 2008 was drier than normal at most Guam and CNMI locations, with 3-month rainfall totals on Guam and in the CNMI generally between 30-35 inches. July and August were particularly dry at most locations as a long-lasting period of tranquil weather persisted. Because of a persistent large-scale pattern of light low-level easterly winds and an unusual lack of tropical cyclones, there were no unusual extremes of heavy rainfall or high winds observed at any Guam or CNMI location. During September, some tropical disturbances contributed to the highest monthly rainfall for the year at many locations. Throughout the 3rd Quarter, light wind conditions led to convective showers that were highly variable. In Central Guam (e.g., Sinajaña and the University of Guam), diurnal thunderstorm activity produced some locally heavier rainfall amounts that were not experienced on other parts of the island. (Note the difference between the Andersen AFB September total of 12.58 versus Sinajaña's 18.21 inches.)

A relatively heavy rainfall event in early October was the first of sufficient magnitude to wash the central mountain streams of Guam of their accumulated burden of algae, palm fronds, dead leaves and choking stream bank vegetation. An unusual effect of the twoyear- running lack of extreme rainfall events on Guam has been the increase in the number of large paper wasp nests overhanging some of the streams. Normally washed out of the stream channels by flash floods, the paper wasps are now becoming an increasing menace to hikers.

Guam and CNMI Rainfall Summary 3rd Quarter 2008

Climate Outlook: For the remainder of 2008, perhaps one tropical storm or typhoon may pass within 200 miles of any Guam or CNMI location (this represents a substantial reduction of risk). If ENSO-neutral conditions persist through the first half of 2009, the typhoon activity may return to near normal in the western North Pacific basin, providing Guam and the CNMI with a slight threat (1 in 15 odds) of adverse effects from a spring tropical cyclone. If La Niña conditions redevelop, then the reduction of tropical cyclone activity noted in the region for the past two years will continue.

Rainfall is anticipated to be near normal to slightly below normal for Guam and the CNMI for the remainder of 2008, and into the first few months of 2009. No extremes of rainfall, wet (i.e., 4 inches or more in a 24-hour period), or dry (i.e., a month with less than 1 inch of rain), are anticipated through the first half of 2009.

Predicted rainfall for Guam and the Mariana Islands from October 2008 through September 2009 is as follows:

source: UOG-WERI