tropical storm

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A cyclonic storm originating in the tropics and having winds ranging from 39 to 73 miles per hour (34 to 63 knots; 63 to 117 kilometers per hour).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A cyclone, within the tropics, in which the wind speed on the surface is between about 30 and 75 miles per hour.