မုန္တိုင္းျပင္းအားအဆင့္မ်ား


Categories

Saffir–Simpson Hurricane Scale
Category Wind speed Storm surge
mph
(km/h)
ft
(m)
5 ≥156
(≥250)
>18
(>5.5)
4 131–155
(210–249)
13–18
(4.0–5.5)
3 111–130
(178–209)
9–12
(2.7–3.7)
2 96–110
(154–177)
6–8
(1.8–2.4)
1 74–95
(119–153)
4–5
(1.2–1.5)
Additional classifications
Tropical
storm
39–73
(63–117)
0–3
(0–0.9)
Tropical
depression
0–38
(0–62)
0
(0)

The scale separates hurricanes into five different categories based on wind, central barometric pressure, and storm surge. The U.S. National Hurricane Center classifies hurricanes of Category 3 and above as major hurricanes. Most weather agencies use the definition for sustained winds recommended by the World Meteorological Organization (WMO), which specifies measuring winds at a height of 33 ft (10 m) for 10 minutes, and then taking the average. By contrast, the U.S. National Weather Service defines sustained winds as average winds over a period of one minute, measured at the same 33 ft (10 m) height.[7][8] Central pressure and storm surge values are approximate and often dependant on other factors, such as the size of the storm and the location. Intensity of example hurricanes is from both the time of landfall and the maximum intensity.[9]

The scale is roughly logarithmic in wind speed, and the top wind speed for Category “c” (c=1, 2, 3, or 4) can be expressed as  miles per hour rounded to the nearest multiple of 5.

The five categories are, in order of increasing intensity:

Category 1

Category 1
Sustained winds 33–42 m/s 64–82 kt
Claudette near landfall
119–153 km/h 74–95 mph
Storm surge 1.2–1.5 m 4–5 ft
Central pressure 980–989 mbar 28.94 inHg

Category 1 storms usually cause no significant structural damage to building structures; however, they can topple unanchored mobile homes, as well as uproot or snap trees. Poorly attached roof shingles or tiles can blow off. Coastal flooding and pier damage are often associated with Category 1 storms.[9]

Examples of storms of this intensity include: Hurricane Alice (1954), Danny (1985), Jerry (1989), Ismael(1995), Gaston (2004), Humberto (2007), and Hanna (2008).

Category 2

Category 2
Sustained winds 43–49 m/s 83–95 kt
Alma approaching land
154–177 km/h 96–110 mph
Storm surge 1.8–2.4 m 6–8 ft
Central pressure 965–979 mbar 28.50–28.91 inHg

Storms of Category 2 are strong enough that they can lift a house, and inflict damage upon poorly constructed doors and windows. Vegetation, poorly constructed signs, and piers can receive considerable damage. Mobile homes, whether anchored or not, are typically damaged, and many manufactured homesalso suffer structural damage. Small craft in unprotected anchorages may break their moorings.[9]

Hurricanes that peaked at Category 2 intensity, and made landfall at that intensity, include Diana (1990),Erin (1995), Alma (1996), Marty (2003) and Juan (2003).

Category 3

Category 3
Sustained winds 50–58 m/s 96–113 kt
Jeanne over the Bahamas
178–209 km/h 111–130 mph
Storm surge 2.7–3.7 m 9–12 ft
Central pressure 945–964 mbar 27.91–28.47 inHg

Tropical cyclones of Category 3 and higher are described as major hurricanes in the Atlantic or Eastern Pacific basins. These storms can cause some structural damage to small residences and utility buildings, particularly those of wood frame or manufactured materials with minor curtainwall failures. Buildings that lack a solid foundation, such as mobile homes, are usually destroyed, and gable-end roofs are peeled off. Manufactured homes usually sustain severe and irreparable damage. Flooding near the coast destroys smaller structures, while larger structures are struck by floating debris. Additionally, terrain may be flooded well inland.[9]

Examples of storms of this intensity include Carol (1954), Alma (1966), Alicia (1983), Fran (1996), Isidore(2002), Jeanne (2004), Lane (2006), and Bertha (2008).

Category 4

Category 4
Sustained winds 59–69 m/s 114–135 kt
Flossie in the Central Pacific
210–249 km/h 131–155 mph
Storm surge 4.0–5.5 m 13–18 ft
Central pressure 920–944 mbar 27.17–27.88 inHg

See also: List of Category 4 Atlantic hurricanes

Category 4 hurricanes tend to produce more extensive curtainwall failures, with some complete roofstructural failure on small residences. Heavy, irreparable damage and near complete destruction of gas station canopies and other wide span overhang type structures are common. Mobile and manufactured homes are leveled. These storms cause extensive beach erosion, while terrain may be flooded far inland.[9]

Hurricanes of this intensity are extremely dangerous to populated areas. Hurricane Ike was the most destructive Category 4 tropical cyclone in recorded history, causing damage in excess of $31.5 billion (2008 USD). With a storm surge of a Category 5 height though the windspeeds were that of a Category 2–3, Ike brought on the greatest recorded storm surge of any Category 4 Atlantic tropical cyclone. Ike also went on to become the most massive Atlantic tropical cyclone ever recorded. Use of radius of outermost closed isobar statistics indicate that Hurricane Ike was the largest tropical cyclone ever observed in the Atlantic basin.[10] The Galveston Hurricane of 1900, the deadliest natural disaster to hit the United States, peaked at an intensity that corresponds to a modern-day Category 4 storm. Other examples of storms at this intensity are Hazel (1954), Carmen (1974), Iniki (1992),Luis (1995), Iris (2001), Charley (2004).

Category 5

Category 5
Sustained winds ≥70 m/s ≥136 kt
Gilbert in the Caribbean Sea
≥250 km/h ≥156 mph
Storm surge ≥5.5 m ≥19 ft
Central pressure <920 mbar <27.17 inHg

See also: List of Category 5 Atlantic hurricanes and List of Category 5 Pacific hurricanes

Category 5 is the highest category a tropical cyclone can obtain in the Saffir-Simpson scale. These storms cause complete roof failure on many residences and industrial buildings, and some complete building failures with small utility buildings blown over or away. Collapse of many wide-span roofs and walls, especially those with no interior supports, is common. Very heavy and irreparable damage to many wood frame structures and total destruction to mobile/manufactured homes is prevalent. Only a few types of structures are capable of surviving intact, and only if located at least three to five miles (four to eight km) inland. They include office, condominium and apartment buildings and hotels that are of solid concrete or steel frame construction, public multi-story concrete parking garages, and residences that are made of either reinforced brick or concrete/cement block and have hipped roofs with slopes of no less than 35 degrees from horizontal and no overhangs of any kind, and if the windows are either made of hurricane resistant safety glass or covered with shutters.[9]

The storm’s flooding causes major damage to the lower floors of all structures near the shoreline, and many coastal structures can be completely flattened or washed away by the storm surge. Storm surge damage can occur up to four city blocks inland, with flooding, depending on terrain, reaching six to seven blocks inland. Massive evacuation of residential areas may be required if the hurricane threatens populated areas.[9]

Storms of this intensity can be severely damaging. Historical examples that reached the Category 5 status and made landfall as such include the Labor Day Hurricane of 1935, the 1959 Mexico HurricaneCamille in 1969, and Gilbert in 1988, Andrew in 1992, Dean, and Felix (2007).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s