We know all about hurricanes.
These monster storms are sometimes the size of entire states, with widespread areas of destructive wind, storm surge and torrential rain and flooding.
But there's a lot of smaller-scale physics that goes on inside these storms, and the biggest mystery to a lot of people is hurricane-spawned tornadoes.
How in the world can we get both a hurricane and tornado at the same time?
The explanation is really not as complicated as you probably think.
First of all, we’re all familiar with the spiral bands emanating from the center of a hurricane. Each band brings an increase in rain intensity and wind and when the hurricane is entirely over water, that’s generally all they produce.
However, as the hurricane (or spiral bands) move over land, friction from terrain, buildings and trees slows the wind near the surface.
Meanwhile, the wind aloft isn’t impacted, and this creates a difference in the wind speeds as you head from the surface aloft.
This difference in wind speed is called wind shear, and you may have heard that spinning up a tornado requires wind shear. So that’s why hurricanes near or over land spawn some tornadoes.
Most hurricane-caused tornadoes develop well out from the eye, with 50 to 200 miles being typical.
The most common location around the hurricane for tornadoes to occur is the right-front quadrant in the direction that the storm is moving.
And although this risk area is well known, and there is usually a tornado watch in effect, keep in mind that a hurricane’s tornadoes usually develop quickly, so warnings aren’t always helpful.
Hurricanes’ tornadoes are also mostly weak ones, EF0 or EF1 on the Enhanced Fujita Scale. However, strong tornadoes sometimes do occur in association with hurricanes, and the most famous one that I remember is the violent twister that occurred in Hurricane Carla in September 1961, which killed eight people.
Since Hurricane Dorian remained offshore, we weren’t in the storm’s mostly likely tornado-producing location. However, those spiral bands were in a more favorable position as the storm approached the Carolinas, and there have been many reports of tornadoes and funnel clouds there. We really dodged a bullet here.