The Bermuda High—it is as mysterious as the Bermuda Triangle.
In summer, it can steer tropical heat into the eastern and southern US. During the Atlantic Hurricane Season, it determines whether a tropical storm visits a Florida political convention or goes for the gumbo near New Orleans. It shapes American weather and, unfortunately, it can be very unpredictable.
Look at the blank area in the satellite picture of the stormy Atlantic. That’s the Bermuda High. It is an area of high atmospheric pressure that drifts through the Atlantic. It is one of several high-pressure areas around 30˚N.
- The air from storms near the equator rises very high and eventually falls back down to earth around 30°North and 30°South.
- This sinking air pushes against the surface creating a high-pressure zone in the atmosphere.
Click to expand image. Credit: National Hurricane Center.
- The winds spin around this high area in a clockwise fashion. (Notice the clouds circling the High.) Storms caught up in these winds are steered to different areas. They stay away from the high pressure.
Think of a high-pressure area as a pinball machine flipper. As the flipper spins around, it steers the pinball. The winds around the Bermuda High steer tropical cyclones towards the west and then northwest. If the high is further out in the Atlantic, the odds are that the cyclones will curve and go out to sea. If the high is further west, there is a good chance that the cyclones can impact the East or Gulf Coasts of the United States.
The problem is the Bermuda High moves. We still are not good at predicting exactly where it will be and how fast it will move. Last week it shifted west and a bit south of its normal position. (It was in the same place as it was in 2004, when Florida got hit by so many hurricanes!) It steered Isaac through the Caribbean islands and up toward Florida.
Last week the high shifted south and west and began steering Isaac towards Florida. Credit: NASA/Goddard Space Flight Center Conceptual Images Lab
Whoops! The Bermuda High shifted east, just far enough away that it no longer controlled Isaac. Isaac turned, kept going north and never turned northeast. Meteorologists watched a front plunge south, but it was too slow to affect the tropical storm. As I write this, Isaac is sailing north heading toward the Mississippi coast.
The Bermuda High shapes our weather, steering heat and storms into the US and Canada. Unfortunately, its movements are still unpredictable, in their own way as mysterious as the Bermuda Triangle.
Evelyn Browning Garriss, historical climatologist, is a longtime writer for The Old Farmer's Almanac. She is also editor of The Browning World Climate Bulletin and has advised farmers, businesses, and investors worldwide on upcoming climate events and their economic and social impact for the past 21 years.