Initially, the Mass of Thunderstorms with Only a Slight Wind

Initially, the mass of thunderstorms with only a slight wind circulation is known as a(n)____________________, or tropical wave. It becomes a(n)____________________ when the winds increase to between 20 and 34 knots and several closed isobars appear about its center on a surface weather map. When the isobars are packed together and the winds are between 35 and 64 knots, it further develops into a(n)____________________. The latter is classified as a(n)____________________ only when its winds exceed 64 knots (74 mi/hr).