- Tropical Depression
An organized system of persistent clouds and thunderstorms with a closed low-level circulation and maximum sustained winds of 38 mph (33 knots) or less.
- Tropical Storm
An organized system of strong thunderstorms with a well defined circulation and maximum sustained winds of 39 to 73 mph (34-63 knots).
An intense tropical weather system with a well defined circulation and sustained winds of 74 mph (64 knots) or higher. In the western North Pacific, hurricanes are called typhoons, and similar storms in the Indian Ocean are called cyclones.