WRAL WeatherCenter Blog

Why are the tropical depressions in the Northern Hemisphere rotating clockwise tonight?

Posted August 4, 2007

MIKE MOSS SAYS:     Barbara,     I wonder if there is a satellite loop that is running backwards (some can be set to loop forward, loop backwards, or "rock" one direction and then the other), as tropical depressions and their stronger relations tropical storms and hurricanes do not rotate clcokwise in the northern hemisphere.

There is one other possible explanation that comes to mind. While the low level circulation in a tropical cyclone is invariably counterclockwise in this hemisphere, the opposite is often true for the "exhaust" at the top of a well organized storm. There, an upper level high pressure center often produces a clockwise outflow of cirrus clouds. If these cirrus clouds are thick enough to be highly visible on satellite imagery, they can make the storm appear to be rotating clockwise, or, for our hemisphere, anticyclonically. Again, though, this is just a veneer of sorts atop the storm and does not represent the flow one would encounter in the lower atmosphere.


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