Which factor contributes to the strength of hurricanes

Warm sea surface temperatures  above 79 degrees Fahrenheit are considered to be the main factor. Warm temperatures result in the formation of water vapor which is the principal source of energy for hurricanes.

Water vapor is the fuel for hurricanes because it releases the latent heat of condensation  when it condenses  to form clouds and rain, warming the surrounding air.

The heat released in this way in tropical thunderstorms is carried away by wind shear which blows off the top off the thunderstorms. However when there is little wind shear, this heat  builds up causing a low pressure zone which in turn causes wind to begin spiraling inward towards the center of this zone thus developing into a hurricane.