A Lesson in Tropical Weather

A Tropical Wave is a shallow tropical low-pressure system (trough) that normally moves east to west (imbedded in the trade wind flow). Ahead of the wave, the wind is generally northeast and behind the wave it becomes southeast. On average, the waves occur every 3 to 5 days during the tropical hurricane season (June to November). Rain squalls and gusty winds to 45 knots occur as the wave passes.

A Tropical Disturbance has a slight rotary circulation with no closed isobars. There are no strong winds associated with a tropical disturbance.

A Tropical Depression has rotary circulation at the surface with several closed isobars. Winds range up to 34 knots (39 mph).

A Tropical Storm has distinct circulation with many closed isobars. Constant winds range from 34 to 63 knots (39-73 mph).

A Hurricane (Tropical Revolving Storm) has a pronounced rotary circulation with sustained winds exceeding 64 knots (74 mph). A "typical" hurricane starts in the doldrums around 10 degrees north and 30 degrees north to 50 degrees west. It moves in a west-north-west direction, and then veers more northwest gradually curving to north and northeast as it reaches 30 degrees north. Spawning areas for hurricanes include the western Caribbean especially for early (June) and late (October and November) season hurricanes. Midseason hurricanes usually begin in the southern North Atlantic, west of the Cape Verde Islands.
Hurricanes are rated into five categories based upon the strength of the sustained winds as described below:
Hurricane Category 1 Wind Speed in MPH 74-95 Storm Surge 4-5 feet
Hurricane Category 2 Wind Speed in MPH 96-ll0 Storm Surge 6-8 feet
Hurricane Category 3 Wind Speed in MPH 110-130 Storm Surge 9-12 feet
Hurricane Category 4 Wind Speed in MPH 130-155 Storm Surge 13-l8 feet
Hurricane Category 5 Wind Speed in MPH l55 plus Storm Surge 18 plus feet