The climate of the Virgin Islands is heavily influenced by much larger climate patterns. For most of the year, trade winds originating in the Atlantic blow across the islands from east to west, lowering both temperatures and humidity from what might be expected at this tropical latitude. However, the winds shift slightly in winter, allowing cold fronts to approach from continental North America; these are known locally as the Christmas winds, and can whip up large waves.
Temperatures are very stable in the Virgin Islands and tend to stay within the same 20 degrees Fahrenheit temperature band year-round. The mercury rarely rises above 90 degrees, and only occasionally drops under 70. National Weather Service data recorded over a 30-year period at the Cyril E. King Airport on St. Croix revealed July and August as the hottest months, with temperatures lowest in December and January.
Rainfall tends to be erratic in the Virgin Islands, meaning any given year can experience very different conditions from the next. On average, annual rainfall totals between 45 and 50 inches, although drier areas can experience under 30 inches, while the wettest areas receive up to 80 inches in a year. Fall typically is the wettest time of year, with peak rainfall occurring in September, October and November. In contrast, spring is the driest time, with March usually experiencing the lowest levels of rainfall.
Generally low and erratic rainfall makes water supply a serious issue for Virgin Islanders, and since the 1930s, laws have compelled residents in the U.S. Virgin Islands to conserve rainwater. Many Islanders are reliant on wells for drinking water, while in the British Virgin Islands, desalination of seawater produces 100 percent of the public water supply on Tortola Island, and 90 percent of Virgin Gorda’s public supply.
