A7a Why do tropical cyclones spawn tornadoes?
Tropical cyclones spawn tornadoes when certain instability and vertical shear criteria are met, in a manner similar to other tornado producing systems. However, in tropical cyclones, the vertical structure of the atmosphere differs somewhat from that most often seen in mid-latitude systems. In particular, most of the thermal instability is found near or below 10,000 feet altitude, in contrast to mid-latitude systems, where the instability maximizes typically above 20,000 feet. Because the instability in TC’s is focused at low altitudes, the storm cells tend to be smaller and shallower than those usually found in most severe mid-latitude systems. But because the vertical shear in TC’s is also very strong at low altitudes, the combination of instability and shear can become favorable for the production of small supercell storms, which have an enhanced likelihood of spawning tornadoes compared to ordinary thunderstorm cells (Novlan and Gray 1974, Gentry 1983, McCaul 1991).
