|MadSci Network: Earth Sciences|
You may find the hurricane brochure published by the National Weather Service useful in understanding hurricanes.
A hurricane is a strong "tropical cyclone". Tropical cyclones are powered by warm sea water. Sea water evaporates into the air above it, making humid air. When this humid air condenses (changes back to liquid, forming clouds and rain), it heats the air around it. This heat causes winds to blow, because the hot air rises and must be replaced by air rushing in from the sides. These winds carry more moist air, which also condenses and heats up, making the tropical storm grow stronger and stronger.
The sea is important to hurricanes: they die out very quickly when they pass over land. But a hurricane doesn't "begin under water".
However, hurricanes have very strong effects on the ocean. First, the winds generate huge waves and rough seas. Second, the winds can push large amounts of water around, causing floods when this water is pushed onto land -- this is called a "storm surge". Fourth, hurricanes dump huge amounts of rain into the sea: this can make the surface waters less salty. Finally, the rough sea created by the hurricane mixes the warm surface water with colder, deeper water, making the surface waters colder.
Try the links in the MadSci Library for more information on Earth Sciences.