Guam's climate is pleasantly warm year-round. The mean annual temperature is 81 degrees; generally, the range is from the low 70s to the middle 80s. The coolest and least humid months, marked by prevailing westerly tradewinds, are in December through February. Although the warmest months are from March through August, the refreshing trade winds blow steadily. The annual rainfall totals 80 to 110 inches. There are two seasons, the dry and the rainy. The dry season, "fanumnangan," begins in December through June. The rainy season, "fanuchanan," falls within the remaining months.

Storms are generally grouped as:

Tropical Depression. Maximum sustained winds of less than 40 miles/hr.
Tropical Storm. Maximum sustained winds greater than 40 and less than 75 miles.
Typhoon: Maximum sustained winds greater than 75 and less than 150 miles per hour.
Super Typhoon: Maximum sustained winds greater than 150 miles per hour.

The wind conditions are defined in one of four catagories:

Condition Four. Guam is always in Condition Four, which means a typhoon can strike within 72 hours.
Condition Three. A typhoon can strike within 48 hours. General preparations should be started.
Condition Two: A typhoon can strike within 24 hours. All non-essential government agencies, including schools and the military, close. Residents are advised to go home and prepare for the storm. All women who are 36 or more weeks pregnant should go to the hospital because the admospheric depression can cause pre-mature labor.
Condition One: A typhoon is imminent and may strike within 12 hours. Only emergency traffic is allowed on roadways.