Despite the local adage that the only seasons in the Keys are the tourist season, the lobster season, and the hurricane season, there are also noticeable seasons in terms of precipitation. The dry season, lasting from November through April, accounts for only 18 to 33% of the annual rainfall. Distribution of rainfall in the Keys during the wet season, May through October, follows a bimodal pattern. The first peak occurs in June and the second during September/October. The bimodal seasonal rainfall distribution reflects the annual movement of a high pressure cell known as the Bermuda High. The Bermuda High migrates westward during the summer months, generally positioning its western edge near the Keys in June. The resulting southeasterly winds bring moisture into the area from the tropical Atlantic Ocean and Caribbean Sea. Winds diminish and rainfall decreases in July and August as the Bermuda High becomes more centered over the Keys. Average winds and rainfall again increases in September and October as the Bermuda High retreats to the east again.

As with temperature, there is a slight difference in total and monthly rainfall between Key West and Tavernier which is probably attributable to Key West’s greater distance from the mainland. Tavernier, approximately 90 miles closer to the mainland, receives more rain from storms forming over the Everglades.

There is also a marked difference in the source and pattern of rainfall in the Keys during the wet and dry seasons. Wet season daily rainfall patterns are dominated by numerous brief, but often intense showers, which usually occur in the early morning. Day-long wet season storms producing excessive rain occur infrequently and are usually associated with tropical storms or hurricanes. In contrast, rainfall during the dry season exhibits a pattern distinct from that observed in convective-type thundershowers. During the dry season, rain usually falls in a few heavy showers over a wide, uniform area ahead of advancing cold fronts and dissipates with the passage of the system.