WRAL WeatherCenter Blog

How many sides on a circle? Perhaps your hurricane awareness spot should have said the winds are strongest on the East side?

Posted May 22, 2007 11:49 a.m. EDT

MIKE MOSS SAYS:       Paul,      I didn't see the awareness spot that you're referring to, but on average, the strongest winds within a tropical cyclone such as a hurricane or tropical storm are located within the eyewall on the right side of the storm, relative to the direction the storm is moving. For a storm moving due north, the strongest winds would indeed tend to be on the east side, but for a storm moving due west, the strongest winds would be on the north side, and so on. The reason for this is that for an idealized northern hemisphere storm with axisymmetric counterclockwise winds, the speed of the storm's forward movement is added to its intrinsic wind field along the right hand side and subtracted along the left hand side, regardless of which geographical direction those areas happen to reside.

A common way to pose an example of this is to consider a stationary storm with 100 mph maximum winds all the way around the storm near the eyewall. If the storm had identical intensity and structure, but was moving west at 20 mph, the maximum winds along the north eyewall would be 120 mph, while those along the south eyewall would be weaker at about 80 mph. Real life is a little more complex than such an idealized example, of course, but the general idea holds true.