Tropical Weather Basics

Tropical Cyclone Definitions

  • Tropical Depression – A tropical cyclone with maximum sustained winds of less than 39 mph.
  • Tropical Storm – A tropical cyclone with maximum sustained winds of 39 to 73 mph.
  • Hurricane – A tropical cyclone with maximum sustained winds of 74 mph or higher.
  • Major Hurricane – A tropical cyclone with maximum sustained winds greater than 110 mph, corresponding to a Category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale.

Watches and Warnings

Hurricane Warning
A Hurricane Warning means that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the warning area. A warning is typically issued 36 hours in advance of the anticipated onset of
tropical-storm-force winds. The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force.

Hurricane Watch
A Hurricane Watch means that hurricane conditions (sustained winds of 74 mph or higher) are possible within the watch area. A watch is typically issued 48 hours before the anticipated onset of tropical-storm-force winds.

Tropical Storm Warning
A Tropical Storm Warning means that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the warning area within 36 hours.

Tropical Storm Watch
A tropical storm watch means that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the watch area, generally within
48 hours.

Saffir-Simpson Hurricane Wind Scale

Category 1: 74-95 MPH Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.

Category 2: 96-110 MPH Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.

Category 3: 111-129 MPH Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.

Category 4: 131-156 MPH Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Category 5: >156 MPH Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.