Tropical Disturbance - Rotary circulation at surface minor or missing but often better developed aloft. There are no closed isobars (lines of equal pressure) nor strong winds. (Reflected on the map as an open circle.)
Tropical Depression - Closed isobars and rotary circulation at surface, highest wind speed is less than 39 MPH. (Open circle)
Tropical Storm - Closed isobars, distinct rotary circulation, and winds from 39 to 73 MPH (34-63 knots). (Open circle with tails)
Hurricane - Closed isobars, strong pronounced rotary circulation, and winds above 73 MPH (63 knots). (Solid circle with tails)
Surge Wave - A "dome" shaped wave that follows the eye and accounts for 9 out of 10 hurricane fatalities.
WARNINGS which may be issued during hurricane conditions:
Gale Warning - Winds 38 to 55 MPH (33-48 knots).
Storm Warning - Winds 55 to 74 MPH (48-64 knots).
Smallcraft Warning - A hurricane is within a few hundred miles.
Hurricane Watch - When a hurricane’s advance threatens coastal or inland regions.
HURRICANE CLASSIFICATION
CLASS/CATEGORY 1
(74-95 MPH — Barometric Pressure of 28.94 inches or more)
Wind Damage: Damage to shrubbery, trees, foliage and unanchored mobile homes. No real damage to other structures. Some damage to poorly constructed signs.
Surge Damage (4-5 feet): Low-lying coastal roads inundated, minor pier damage. Some small craft in exposed anchorages torn from their moorings.
CLASS/CATEGORY 2
(96-110 MPH — Barometric Pressure 28.50 to 28.93 inches)
Wind Damage: Some trees blown down. Major damage to exposed
mobile homes and poorly constructed signs. Some damage to roofing. No major damage to buildings.
Surge Damage (6-8 feet): Coastal roads and low-lying escape routes inland cut off by rising water 2-4 hours before arrival of the hurricane center. Considerable damage to piers. Marinas flooded. Evacuation of some shoreline residences and low-lying island areas required.
CLASS/CATEGORY 3
(111-130 MPH — Barometric Pressure 27.91 to 28.49 inches)
Wind Damage (111-130 MPH: Large trees blown down. Practically all poorly constructed signs blown down. Some roofing, window, and door damage. Some structural damage to small buildings. Mobile homes destroyed.
Surge Damage (9-12 feet): Many small coastal structures destroyed. Large structures damaged by waves and floating debris. Low-lying escape routes cut by rising water 3-5 hours before arrival of hurricane center. Flat terrain, 5 feet or less above sea level, flooded inland 8 miles or more. Evacuation of low-lying residences possibly required.
CLASS/CATEGORY 4
(131-155 MPH — Barometric Pressure 27.17 to 27.90 inches)
Wind Damage: Shrubs and trees blown down. All signs down.
Extensive damage to roofing, windows and doors. Complete failure of roofs on many smaller structures. Complete destruction of mobile homes.
Surge Damage (13-18 Feet): Flat terrain, 10 feet or less above sea level, flooded inland as far as 6 miles. Major damage to lower floors of structures near shore. Low-lying escape routes cut off 3-5 hours before the hurricane center arrives. Evacuation of all residences within 500 yards and all single story residences within 2 miles of shore possibly required.
CLASS/CATEGORY 5
(156 MPH or Greater — Barometric Pressure less than 27.17 inches)
Wind Damage: Complete failure of roofs on many residences
and industrial buildings. Extensive shattering of glass windows and doors. Some complete building failure. Small buildings overturned or blown away. Complete destruction of mobile homes.
Surge Damage (19 feet and Above): Major damage to lower floors of all structures less than 15 feet above sea level within 500 yards of routes cut by rising water 3-5 hours before hurricane center arrives. Massive evacuation of residential areas on low ground within 5-10 miles of shore possibly required.
