Tropical cyclones are systems of cyclonic rotating winds characterized by a rapid decrease in pressure and increase in winds toward the center of the storm. Their dimensions can vary from 60 nautical miles for a small cyclone, to over 1000 nautical miles for larger systems.
Three stages of wind intensity are associated with tropical cyclones:
- Tropical Depression - 38mph (33kts) or less
- Tropical Storm - 39-73mph (34-63kts)
- Hurricane - Greater than 73mph (63kts)
Most tropical cyclones are seasonal phenomena, forming during the warmer seasons over warm tropical waters, and often moving into mid-latitudes. Mature tropical cyclones are normally composed of several distinct features: the eye, or center, which is an area of light winds and the lowest pressure; the eye wall, a circular ring of towering cumulonimbus clouds, extremely strong winds, and heavy rains surrounding the eye; and bands of rain showers and thunderstorms which spiral into the eye wall. Damage from tropical cyclones is caused by strong winds, flooding from heavy rains, thunderstorm-induced tornadoes, and high storm surge along coastal regions. Tropical cyclone conditions of readiness indicate the strength of winds expected and the time they will arrive and not when the eye, or center, of the cyclone will pass.
Hurricane Condition II indicates that hurricane force winds are expected within 24 hours.