By Times Staff Writer
Published May 29, 2005
By international agreement, tropical cyclone is the general term for all cyclonic, counterclockwise circulations originating over tropical waters, classified by form and intensity as follows:
Tropical disturbance: A rotary circulation with little to no development on the ocean surface but better development in the upper atmosphere and no strong winds, a common phenomenon in the tropics.
Tropical depression: A low-pressure area with some rotary circulation on the ocean surface and a sustained wind speed of less than 39 mph.
Tropical storm: A low-pressure area with a distinct rotary circulation and sustained wind speeds of 39 to 73 mph.
Hurricane: A low-pressure area with a strong and pronounced rotary circulation and a sustained wind speed of at least 74 mph.