The Sea Breeze

If you’re going to be travelling to a coastal location along the Gulf of Mexico or East Coast, there’s a weather phenomenon I want you to be familiar with. It’s called a sea breeze, and it can turn a tranquil day into a stormy late afternoon with little notice.

Land heats up several times faster during the day than water (lakes and oceans) do. This also creates a pressure difference between land and sea. The pressure difference creates the sea breeze, which is a circulation composed of two opposing flows; one at the surface (called the sea breeze) and one aloft (which is a return flow).

Take a look at this diagram as we go through the sea breeze process:

At the surface, the sun warms both the ground and ocean at the same rate. However, since the heat in the ground is not absorbed well it returns it heat to warm the air. The warmed air, with its decreased density, begins to rise (1). The rising air creates a weak low pressure area (called a thermal low) due to a decrease in air mass at the surface (2). Typically, from 3,000 to 5,000 feet (1,000 to 1,500 meters) above this low pressure, as the air cools, it begins to collect resulting in an increase in pressure, creating a “high” (3).

These differences in pressures over land, both at the surface and aloft are greater than the differences in pressures over water at the same elevations (4 and 5). Therefore, as the atmosphere seeks to reestablish equal pressure both onshore and offshore, two high pressure to low pressure airflows develop; the offshore flow aloft (6) and surface onshore flow, called the sea breeze (7).

The sea breeze acts as a boundary, like a cold front, and can be the focusing mechanism for thunderstorm development.  In Florida, the amount of sunshine and prevailing surface wind over the state has a large impact on sea breeze thunderstorms. If the wind is relative calm then the sea breeze can move will inland but with only scattered thunderstorms occurring about 1/3rd of the way across the peninsula.

Light west wind (5-10 mph) keeps the sea breeze front confined to the eastern coast but also makes for more widespread thunderstorms along the boundary. Stronger west winds prevent can the sea breeze front from moving onshore, or forming at all, so no thunderstorms will occur. With prevailing east winds, they actually help push the sea breeze front and thunderstorms as much as half way across the peninsula.

The most explosive thunderstorm development often occurs when two different sea breezes interact with each other. This happens in Florida when the Gulf of Mexico sea breeze collides with the Atlantic Ocean sea breeze somewhere in the middle of the state. Thunderstorms can be strong to severe, produce extremely heavy rain and be very slow-moving.



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