Although Storm Warning Flags are no longer officially displayed, the designations (Small Craft Warning, etc) are still referred to in marine forecasts. 

Storm Warning Flags
Small Craft Warning 21-38 mph (18-33 kts)	Gale Warning 39-54 mph (34-47 kts)	Storm Warning 55-73 mph (48-63 kts)	Hurricane Warning 74+ mph (64+ kts)

  
 The Beaufort Scale, devised in 1805 by Sir Francis Beaufort (1774-1875), is a system for estimating wind strengths without the use of instruments, based on the effects wind has on the physical environment. The behavior of smoke, waves, trees, etc., is rated on a 13 point scale of 0 (calm) to 12 (hurricane). 

Beaufort Scale
FORCE	DESC	MPH	EFFECTS
0	Calm	0-1	Land- Smoke rises vertically Water- Like a mirror
1	Light Air	1-3	L- Rising smoke drifts W- Small ripples
2	Light Breeze	4-7	L- Leaves rustle W- Small wavelets, wind fills sail
3	Gentle Breeze	8-12	L- Light flags extend W- Large wavelets, sailboats heel
4	Moderate Breeze	13-18	L- Moves thin branches W- Working breeze, saiboats at hull speed
5	Fresh Breeze	19-24	L- Small trees sway W- Numerous whitecaps, time to shorten sails
6	Strong Breeze	25-31	L- Large tree branches move W- Whitecaps everywhere, sailboats head ashore, large waves
7	Moderate Gale	32-38	L- Large trees begin to sway W- Much bigger waves, some foam, sailboats at harbor
8	Fresh Gale	39-46	L- Small branches are broken from trees W- Foam in well marked streaks, larger waves, edges of crests break off
9	Strong Gale	47-54	L- Slight damage occurs to buildings W- High waves, dense spray, visibility affected
10	Whole Gale	55-63	L- Large trees uprooted, considerable building damage W- Very high waves, heavy sea roll, surface white with spray and foam, visibility impaired
11	Storm	64-74	L- Extensive widespread damage W- Exceptionally high waves, small to medium ships obscured, visibility poor
12	Hurricane	74+	L- Extreme destruction W- Waves 40+', air filled with foam and spray, visibility restricted

    
The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Herbert Saffir, a consulting engineer in Coral Gables, Fla., and Robert Simpson, who was then director of the National Hurricane Center, developed the scale in the early 1970s. 

Saffir-Simpson Hurricane Scale
CAT	TYPE	MPH	SURGE	DAMAGE
-	Depression	< 35	-	-
-	Tropical storm	39-73	-	-
1	Hurricane	74-95	4-5 feet	minimal
2	Hurricane	96-110	6-8 feet	moderate
3	Hurricane	111-130	9-12 feet	extensive
4	Hurricane	131-155	13-18 feet	extreme
5	Hurricane	155+	18+ feet	catastrophic

Category One Hurricane:
74-95 mph (64-82 kt or 119-153 km/hr)
Storm surge generally 4-5 ft above normal. No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs. Also, some coastal road flooding and minor pier damage. Hurricanes Allison of 1995 and Danny of 1997 were Category One hurricanes at peak intensity.
 

Category Two Hurricane:
Winds 96-110 mph (83-95 kt or 154-177 km/hr)
Storm surge generally 6-8 feet above normal. Some roofing material, door, and window damage of buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of the hurricane center. Small craft in unprotected anchorages break moorings. Hurricane Bonnie of 1998 was a Category Two hurricane when it hit the North Carolina coast, while Hurricane Georges of 1998 was a Category Two Hurricane when it hit the Florida Keys and the Mississippi Gulf Coast.
 

Category Three Hurricane:
Winds 111-130 mph (96-113 kt or 178-209 km/hr)
Storm surge generally 9-12 ft above normal. Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off trees and large tress blown down. Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane center. Flooding near the coast destroys smaller structures with larger structures damaged by battering of floating debris. Terrain continuously lower than 5 ft above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying residences with several blocks of the shoreline may be required. Hurricanes Roxanne of 1995 and Fran of 1996 were Category Three hurricanes at landfall on the Yucatan Peninsula of Mexico and in North Carolina, respectively.
 

Category Four Hurricane:
Winds 131-155 mph (114-135 kt or 210-249 km/hr)
Storm surge generally 13-18 ft above normal. More extensive curtainwall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape routes may be cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles (10 km). Hurricane Luis of 1995 was a Category Four hurricane while moving over the Leeward Islands. Hurricanes Felix and Opal of 1995 also reached Catgeory Four status at peak intensity.
 

Category Five Hurricane:
Winds greater than 155 mph (135 kt or 249 km/hr)
Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destructon of mobile homes. Severe and extensive window and door damage. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required. Hurricane Mitch of 1998 was a Category Five hurricane at peak intensity over the western Caribbean. Hurricane Gilbert of 1988 was a Category Five hurricane at peak intensity and is the strongest Atlantic tropical cyclone of record.

Source: National Oceanic and Atmospheric Administration (NOAA)

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