So rain clouds tend to be these towering clouds, while stratus clouds tend only to be associated with drizzle. Towering rainclouds of this sort are called cumulonimbus. Rain is formed when water droplets that have merged are to large to be supported by the surrounding air currents. A minimal hurricane requires sustained winds of 74 mph or more. Hurricanes generally move from east to west .
Hurricanes often originate as clusters of strong thunderstorms .
When these clusters cross into waters with surface temperatures of 82 degrees or higher, they can intensify into hurricanes. 82 degrees is the minimum water temperature that can support a hurricane. When wind speeds in a tropical low exceed 74 mph, the low is then known as a hurricane. The greater the wind speed is, the larger the category number, with category five being the most destructive with speeds greater than 155 mph. Hurricane Dennis Presentation of satellite image of Hurricane Dennis as it passes over the waters west of the Carolinas.