Land and Sea Breezes

Sea breezes are a type of mesoscale coastal wind caused by thermal circulation. In the day, the land heats more quickly than the adjacent water causing a shallow thermal low over the land. The air over the water remains relatively cooler giving rise to a shallow thermal high pressure region. The strongest pressure gradients exist at the land-sea boundary and that is where the strongest winds form.

At night, the land cools more quickly than the water causing a high pressure area over the land and a relatively lower pressure area over the water. With the higher pressure over land, the wind blows from the land out over the water, producing a land breeze.

Due to the presence of the Gulf of Mexico, land and sea breezes are a major factor in surface winds in summer months. Considering a no-force gradient, when the land warms to 7-10 degrees F above local bay and gulf temperatures, a sea breeze will develop in any season, but is more pronounced in the summer months June to early September.

During an average summer day (24 hours), the following usually occurs:

Between midnight and 0800-0900 local, the land is cooler then water and a land breeze sets up as winds drain from the NNW-NE 3-5 knots. When the land warms to above the bay temperatures (generally 0930-1030 local) the wind shifts to the SE, 120-160 degrees, at 5-8 knots. By early afternoon (1300 local) the true sea breeze veers and sets in from the SSW (220) at 8-12 knots, increasing to 15-20 knots at max land heating (1400-1600 local). The SW flow continues as the winds gradually decrease as evening cooling occurs. As the land slowly cools to below the surrounding water, the winds initially become light and variable, then calm by 2200 local. By midnight, the air has cooled enough for the land breeze to set up again.
In August, when the Bermuda High has moved to its northern-most position over the central North Atlantic, the sea breeze maintains a SE component throughout the day. During August and early September, the SSW sea breeze does not normally occur.

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