850mb map from IntellicastGothamist had the heat on at night last week when we were in central New York and northern Vermont so we were ill-prepared to return to the sauna of Manhattan. We have a Bermuda High to thank for the hot and sticky weather this week. The vigor of atmospheric circulation results from the temperature difference between the equator and poles. Temperatures near the equator stay relatively constant throughout the year. As the northern hemisphere heats up through spring and summer the equator-pole temperature difference decreases, and the atmosphere slows down. The pattern of atmospheric circulation is more complicated but is related to the strength of the circulation as well as the shape and positions of the continents and oceans.

The Bermuda High is a semi-permanent high pressure system that generally sits over the eastern Atlantic during winter and drifts westward, and strengthens, during the summer. Air circulates anticyclonically, or clockwise in the northern hemisphere, around high pressure systems. As the Bermuda High moves westward it pumps warm, humid subtropical air over the eastern U. S. You can see from the map at left that the system is the main factor in the weather for half the country. If you are not a hot weather fan you're in luck, a cold front should pass through late Thursday and push the High back out to sea.