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    Although Storm Warning Flags are no longer officially displayed, the designations (Small Craft Warning, etc) are still refered to in marine forecasts.
Storm Warning Flags
penant penant
penant
flag flag
flag
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)
For info about International Marine Signal Flags go here...
    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 behaviour 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 Wind Scale is a 1-5 rating based on a hurricane's sustained wind speed. This scale estimates potential property damage. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and damage. Category 1 and 2 storms are still dangerous, however, and require preventative measures.
    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. It was updated in 2010 removing references to "storm surge." Surge information for specific storms is now included in local hurricane statements.
Saffir-Simpson Hurricane Scale
CAT
TYPE
MPH
DAMAGE
-
Depression
< 35
-
-
Tropical storm
39-73
-
1
Hurricane
74-95
moderate
2
Hurricane
96-110
extensive
3
Hurricane
111-129
extreme
4
Hurricane
130-156
catastrophic
5
Hurricane
157+
catastrophic
Category One Hurricane:
Winds 74-95 mph (64-82 kt or 119-153 km/h)

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. 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/h)

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. 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 111-129 mph (96-112 kt or 178-208 km/h)

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. 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 130-156 mph mph (113-136 kt or 209-251 km/h)

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. 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 157 mph (137 kt or higher or 252 km/h or higher)

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. 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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