Hurricanes are best known for the associated wind, storm and rain threats. But there is another very common threat that occurs in the outer rainbands: tornadoes.

Hurricane Helene, which is heading toward Florida’s northwest coast, has already triggered tornado warnings on Thursday, and tornado warnings are in effect across South Florida until 8 p.m.

Although no direct impacts are expected in South Florida, the region is still feeling the effects of the storm, which is expected to make landfall as a Category 3.

Tornadoes are typically found on the eastern side of the hurricane, and in fact it is known as the strongest side or “dirty” side of the system.

Waterspouts are commonly seen in South Florida, but tropical tornadoes arise from the increased wind shear that occurs as the outer band, called squall lines, moves onshore.

The outer bands shoot away from the center of the circulation and move quickly. As they move on land, the wind on the surface decreases. But higher up in the atmosphere the wind remains strong.

This contrast is called wind shear – a change in wind speed (or direction) at different heights in the sky. This results in fast but frequent spin-up tornadoes.

The change in direction occurs as the hurricane itself undergoes a natural counterclockwise rotation, but the outer bands move away from the center, resulting in a slightly different direction of these winds.

These are typically very short-lived and weak compared to the large supercell tornadoes that arise from individual rotating thunderstorms.