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Bermuda High Is Cause of Most East Coast Summer Heat

UPDATED July 5, 2013

By Weatherbug Meteorologists


For long periods of time each summer the East Coast suffers from the uncomfortable 3-Hs, hazy, hot and humid. This yearly occurrence is caused by the Bermuda, aka "Heat Pump" High.

This well-known area of high pressure forms over the Atlantic Ocean during the summer. Located southeast of the Mid-Atlantic Coast near Bermuda, this high`s summertime shift is a key factor for most of the eastern U.S. weather as well as for the Atlantic hurricane season.

The Bermuda High can form over the Atlantic from late-spring till early fall. The clockwise circulation around the high brings hot and humid wind to the East during the summer, especially in the Southeast. It can often lead to many days to weeks of hot and sticky weather common during East Coast summers.

Not only does it heat up summer-time temperatures in the East, but the Bermuda High can affect the intensity of tropical storms and hurricanes. The sinking motion caused by this high pressure causes the air to become drier and warmer. This drier and warmer air can suppress cloud formation off the water, and the sun is better able to directly heat the ocean surface. This can allow water temperatures to increase, and warmer sea surface temperatures can be major breeding grounds for strengthening and aiding the formation of hurricanes.

Due to the clockwise direction of flow it causes, African easterly waves are often forced away from the coast of West Africa towards North America and the Caribbean. This can also help form tropical storms. Depending on where the high lies each summer, the exact location of the high pressure system can be a major factor in determining the direction hurricanes will go.

If it remains close to the Atlantic Coast, it tends to push along tropical waves in the Caribbean Sea and the Gulf of Mexico. If it shifts too far out to sea, the low pressure system that typically exists in the gap behind it along the East Coast can force storms up the Southeast Coast. A normal Bermuda High often directs hurricanes to move up the East Coast and out to sea.

In general, when the Bermuda High is displaced more south and westward, it can stretch its western edges close to and even over the East Coast. If and when this set-up occurs, the eastern U.S. coastline can be left extremely susceptible to hurricanes.

During the winter, the Bermuda High shrinks and moves to the south of the Azores, islands in the east-central Atlantic. This allows more variable weather to return to the East Coast just as autumn begins and the hurricane season nears its end.

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