As Irene bears down on the Northeast, meteorologists are keeping track of the storm's wind intensity using the Saffir-Simpson Hurricane Wind Scale, originally developed by wind engineer Herb Saffir and meteorologist Bob Simpson. In general, damage rises by about a factor of four for every category increase. The scale does not address the potential for other hurricane-related impacts such as storm surge, rainfall-induced floods and duration of the wind, all of which can increase the damage.
Category 1: Sustained winds 74-95 mph. Danger from flying debris; possible damage to poorly constructed roofs; damage to awnings, shingles, siding, gutters; broken windows. Large tree branches can snap, shallow rooted trees can topple. Extensive damage to power lines and poles resulting in power outages lasting a few to several days.
Category 2: Sustained winds 96-110 mph. Substantial risk from flying and falling debris. High probability of broken windows from windborne debris. Roof damage, failure of screen-in porches and enclosures. Commercial signage, fences and canopies will be damaged, often destroyed. Falling and broken glass will pose significant danger even after the storm. Many shallowly rooted trees will be snapped or uprooted. Near-total power loss with outages lasting several days to several weeks. Potable water could become scarce as filtration systems fail.
Category 3: Sustained winds 111-130 mph. High risk of injury or death from flying and falling debris. High percentage of roof and siding damage. Complete failure of older metal buildings likely; older unreinforced masonry buildings can collapse. Numerous windows will be blown out of high-rise buildings. Falling and broken glass will pose significant danger even after the storm. Most commercial signage, fences and canopies will be destroyed. Many trees will be snapped and uprooted. Electricity and water will be unavailable for several days to a few weeks.
Category 4: Sustained winds 131-155 mph. Large amounts of windborne debris will be lofted into the air posing very high risk of injury or death. Flying debris will break all unprotected windows and penetrate some protected windows. Even well-built homes can sustain severe damage to to roofs, walls, windows and doors. High percentage of structural damage to top floors of apartment buildings. High percentage of collapse of older unreinforced masonry buildings. Most windows will be blown out of high rise buildings. Falling and broken glass will pose significant danger even after the storm. Nearly all commercial signage, fences and canopies will be destroyed. Most trees will be snapped or uprooted and power poles downed. Power outages wil last weeks, possibly months. Long-term water shortages. Most areas will be uninhabitable for weeks or months.
Category 5: Sustained winds greater than 155 mph. Very high risk of injury or death from falling and flying debris even if indoors in a frame house. Windborne debris will damage all unprotected windows and many protected ones. A high percentage of frame homes, industrial buildings and low rise apartment buildings will be destroyed. Most unreinforced masonry will collapse. Nearly all windows will be blown out of high rise buildings. Falling and broken glass will pose significant danger even after the storm. Nearly all commercial signage, fences and canopies will be destroyed. Most trees will be snapped or uprooted and power poles downed. Power outages wil last weeks, possibly months. Long-term water shortages. Most areas will be uninhabitable for weeks or months.
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