Large bodies of water, such as oceans, gulfs, sounds and large lakes, have a profound effect on the climate of coastal areas. Many meteorologists give two forecasts in a region, one for the 5 miles closest to a shoreline and one for inland areas, because the difference between the expected temperatures and precipitation is so great.
Bodies of water have a damping effect on the swing in temperatures of coastal areas. That is, while inland regions can quickly decrease in temperature from the fall to winter seasons, shoreline towns are kept warmer by the water's effect on the air. This is due to water's high heat capacity compared to both air and land. Therefore, shoreline towns will experience warmer winters and cooler summers than inland communities.
Shoreline communities experience an interesting dynamic between the air over water and the air over land. Air tends to move from cooler areas toward warmer areas, and the sun often dictates whether the land or sea is cooler. During the daytime, the air onshore is warmer than the air over the sea, so the wind blows from the sea to the land. At night, the opposite occurs since the air over the sea is warmer.
Bodies of water not only affect how much precipitation a shoreline gets, but also what type of precipitation falls. The Gulf of Mexico, for example, brings warm moist air over the Gulf Coast region, which results in thunderstorms, heavy rains, fog and, most notoriously, hurricanes. This severe precipitation occurs when the warmer, moist air collides with a mass of cooler, dry air. According to theweatherprediction.com, coastal Mississippi averages about 61 inches of rainfall per year while regions to the north average about 50 inches per year. In northern climates such as the Great Lakes region, the monstrous lakes produce what is called lake effect snow in the winter, in which moisture from a lake is evaporated then quickly blown toward its shore, where it is deposited in the form of snow.
The direction of oceanic currents greatly affects the climate of coastal towns. The Gulf Stream current, which runs rapidly up the eastern seaboard from the Caribbean, bringing relatively warm water up into cooler climates. This current runs into the Gulf of Mexico, where it has a chance to increase in temperature before it runs back down around Florida then turns northward. On the West Coast of the United States, the current runs from the Gulf of Alaska down along the Pacific Coast, bringing colder water with it.