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Ask the Meteorologist: Why do tropical systems sometimes spawn tornadoes?
Tropical systems can often spawn tornadoes. WRAL meteorologist Chris Michaels explains why.
As tropical systems move over land, Michaels said the friction increases. This creates wind shear, which causes air to start spinning in the atmosphere. Tornadoes then become possible.
The Storm Prediction Center (SPC) said there are four necessary ingredients for tropical systems to spawn tornadoes: Moisture, instability, lift and vertical shear.
Moisture
Moisture is pretty self-explanatory. We refer to it as humidity, which happens when water vapor is present in the air.
Instability
According to the National Weather Service (NWS), instability refers to the tendency for air parcels to accelerate when they are displaced from their original position – especially, the tendency to accelerate upward after being lifted. The NWS said instability is a prerequisite for severe weather, which means the greater the instability, the greater the potential for severe weather.
“Instability occurs when a parcel of air is warmer than the environmental air and rises on its own due to positive buoyancy,” the NWS said on its website.
Instability is what allows air in the low levels of the atmosphere to rise into the upper levels of the atmosphere.
Without instability, the NWS said the atmosphere will not support deep convection and thunderstorms.
Lift
Lift occurs when the air rises.
“Lift is what gives a parcel of air the impetus to rise from the low levels of the atmosphere to the elevation where positive buoyancy is realized,” according to the NWS.
Lift is often referred to as a trigger mechanism, the NWS said.
Vertical shear
The NWS defines vertical shear as the change in the wind’s direction and speed with height.
Vertical wind shear helps determine potential storm severity.
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The risk Monday is low, but isolated tornadoes are still possible. Stick with WRAL News for the latest weather updates.