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How do hurricanes form?

Last Updated: Aug 15, 2014 03:27PM CDT

 

According to Landsea (2000), before tropical cyclone development and further strengthening can transpire, several essential environmental circumstances must be met (Gray 1968, 1979):

 

1. Warm ocean waters (of at least 26.5 °C) throughout an adequate depth (at least about 50 m deep) - are required to stimulate the tropical cyclone heat engine. 

 

2. An atmosphere in which temperatures drop quick enough with height such that it is potentially unstable to moist convection. 

 

3. Plentiful moisture throughout the atmosphere. 

 

4. A minimum distance of around 500 km from the equator. For tropical cyclone development to take place, there is a prerequisite for ample amounts of the Coriolis force to provide for near gradient wind balance to happen. 

 

5. A pre-existing near-surface disturbance with ample vorticity and convergence. Tropical cyclones cannot be created spontaneously. To develop, they require a weakly organized system with substantial spin and low level inflow.

 

6. Low magnitudes (less than about 10 m/s) of vertical wind shear between the ocean's surface and the upper troposphere. Vertical wind shear is the horizontal wind change with height. Large values of vertical wind shear disturb the incipient tropical cyclone and can put a stop to genesis, or, if a tropical cyclone has already developed, large vertical shear can weaken or wipe out the tropical cyclone by interfering with the organization of deep convection around the cyclone center. High vertical wind shear can entrain ambient air into the cyclone and can also tilt the vortex, which could cause the mid-level and low-level center to decouple, weakening the tropical cyclone.

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