Wx Savvy | Hurricanes

How Do Hurricanes Form?

Hurricanes form over the warm tropical waters because the warm ocean water is the fuel for the storm. In fact, the water must be about 81 degrees F for hurricanes to thrive(1). There is a band across the globe near the equator called the Intertropical Convergence Zone or ITCZ, and this is the general area where hurricanes live.

(Hurricane Fran)

It all starts as a complex of thunderstorms which then begins to organize together. Once it starts to circulate around a central area of low pressure it may become a tropical depression (sustained winds of 23-39 MPH). Then as it gains strength it may become a tropical storm (sustained winds of 39-74 MPH). Once it reaches 74 MPH it will be a hurricane.

Most hurricanes that threaten the US are from the Atlantic Basin. Atlantic hurricanes originate anywhere from the Caribbean or even off the African coast. The reason for this is that the trade winds are the dominate winds in this region, and they blow from Africa to the Gulf of Mexico. Therefore, they steer these hurricanes in that direction. Usually when a hurricane gets close to the US, it is steered to the Northeast by our dominant winds called the Westerlies. "Westerlies" means that the wind is coming from the West and would push a hurricane East and away from the US. Sometimes our weather pattern in the US is such that there is no strong weather feature to push the storm back out over the ocean, and that means it may make landfall.

When hurricanes get into colder waters, they fall apart. Or if they come over land, they lose the warm water fuel and thus weaken quickly.

(1) http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/home.rxml