Showing posts with label Saffir–Simpson. Show all posts
Showing posts with label Saffir–Simpson. Show all posts

Wednesday, 13 March 2013

Hurricanes and typhoons

Hurricanes
A hurricane is a type of tropical cyclone or severe tropical storm that forms in the southern Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern Pacific Ocean. A typical cyclone is accompanied by thunderstorms, and in the Northern Hemisphere, a counterclockwise circulation of winds near the earth’s surface.



Typhoons
A typhoon is a mature tropical cyclone that develops in the northwestern part of the Pacific Ocean between 180° and 100°E.


What does a hurricane or typhoon need?
Like any tropical cyclone, there are different main requirements for hurricane or typhoon formation and development: 

  • sufficiently warm sea surface temperatures, 
  • atmospheric instability, 
  • high humidity in the lower to middle levels of the troposphere, 
  • enough Coriolis force to develop a low pressure center, 
  • a pre-existing low level focus or disturbance, and 
  • low vertical wind shear.






The Saffir-Simpson hurricane wind scale
The Saffir-Simpson hurricane wind scale classifies hurricanes into five categories based on their sustained wind speed at the indicated time. The Saffir-Simpson Hurricane Wind Scale provides information on wind impacts only. The scale does not address the potential for other hurricane-related impacts, such as storm surge, rainfall-induced floods, and tornadoes.

Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and property.  Category 1 and 2 storms are still dangerous, however, and require preventive measures.



To prepare for a hurricane, you should take the following measures:

  • To begin preparing, you should build an emergency kit and make a family communications plan.
  • Know your surroundings.
  • Learn the elevation level of your property and whether the land is flood-prone. This will help you know how your property will be affected when storm surge or tidal flooding are forecasted.
  • Identify levees and dams in your area and determine whether they pose a hazard to you.
  • Learn community hurricane evacuation routes and how to find higher ground. Determine where you would go and how you would get there if you needed to evacuate.
  • Make plans to secure your property:
  • Cover all of your home’s windows. Permanent storm shutters offer the best protection for windows. A second option is to board up windows with 5/8” marine plywood, cut to fit and ready to install. Tape does not prevent windows from breaking.
  • Install straps or additional clips to securely fasten your roof to the frame structure. This will reduce roof damage.
  • Be sure trees and shrubs around your home are well trimmed so they are more wind resistant.
  • Clear loose and clogged rain gutters and downspouts.
  • Reinforce your garage doors; if wind enters a garage it can cause dangerous and expensive structural damage.
  • Plan to bring in all outdoor furniture, decorations, garbage cans and anything else that is not tied down.
  • Determine how and where to secure your boat.
  • Install a generator for emergencies.
  • If in a high-rise building, be prepared to take shelter on or below the 10th floor.
  • Consider building a safe room.



Monday, 11 March 2013

Saffir–Simpson hurricane wind scale

The Saffir–Simpson hurricane wind scale is a 1 to 5 rating based on a hurricane's sustained wind speed. This wind scale estimates potential property damage. 
  
Saffir–Simpson hurricane wind scale
Category
Wind speeds
Damage
Five
≥252 km/h
catastrophic damage
Four
209–251 km/h
catastrophic damage
Three
178–208 km/h
devastating damage
Two
154–177 km/h
extensive damage
One
119–153 km/h
some damage










Category 1
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

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

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
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

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.