Florida Rainy Season

Sometime between late-May and mid-June, the Florida summer rainy season begins. This time of year in Florida is marked by the onset of showers and thunderstorms associated with the daily migration of the East and West Coast sea breezes. Since the ocean is a transparent liquid the water is warmed by the sun to a greater depth than the land and as a result the water will gain and lose heat more slowly than the land mass. 

As the land surface heats, it in turn heats the air above it. The warm air is less dense and tends to rise creating lower air pressure over the land than over the water. The cooler air over the water is more dense and then flows inland creating a "sea breeze". 

The incoming sea breeze creates a sea breeze front or boundary which acts as a lifting mechanism resulting in the warmer air rising up to higher altitudes creating cumulus clouds. Once the summer humidity establishes itself over Florida you begin to see the building towering cumulus clouds and the development of showers and thunderstorms with these boundaries. 

Over Florida, these sea breeze fronts move inland from both coasts (Gulf and Atlantic) which is why Florida is marked by numerous thunderstorms which produce heavy rains and frequent lightning. Often these sea breeze fronts will collide causing severe thunderstorms to develop.

The onset of the rainy season is tied to the northward and southward migration of the North Atlantic Subtropical high pressure ridge, often called the Azores-Bermuda Ridge or just the Bermuda high. The location of the ridge controls the low level winds and the moisture availble for the Gulf and Atlantic sea breezes. 

During the winter months this ridge is weak and depressed southward which allows cold fronts to penetrate southward across Florida with continental high pressure dominating the weather over Florida. During the spring and fall months, the ridge drifts northward acorss Florida cutting off the cold fronts from the north. At this time we will experience the classic dry months (Oct-Nov in the fall and Apr-May in the spring). As the ridge drifts northward and builds during late spring and early summer deep tropical moisture overspreads Florida and sets us up for the daily sea breeze induced thunderstorms common during the rainy season. 

Fred Pickhardt

Ocean Weather Services