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How strong will Helene be? Hurricane category forecast explained.
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How strong will Helene be? Hurricane category forecast explained.

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As monster storms like Helene approach the U.S., meteorologists use five categories to signal the life-threatening impacts to residents in their path.

This scale – officially known as the Saffir-Simpson Hurricane Wind Scale – is a rating based on maximum sustained wind speed, which ranges from 74 to 157 mph or greater.

But it’s important to note that the scale doesn’t account for potentially deadly hurricane hazards like storm surge, rainfall, flooding, and tornadoes. These hazards require people to take protective measures, including evacuating areas vulnerable to storm surge.

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Hurricane Helene, which is now barreling toward landfall on Florida’s Gulf Coast on Thursday, will continue to strengthen in wind speed over the next few days. As it strengthens, its winds will also increase in categories on the official hurricane wind scale, which ranges from 1 to 5.

What is the Saffir-Simpson Hurricane Wind Scale?

The Saffir-Simpson scale compares wind speeds to examples of the type of damage and impact those winds can cause in the U.S. In general, damage increases by about a factor of four for each category increase.

The scale was developed in 1969 by engineer Herbert Saffir as part of a United Nations project. It was later modified in the early 1970s by meteorologist Robert Simpson and has since become an integral tool for warning the public of the potential impacts of hurricanes of varying intensity, according to the National Hurricane Center.

How much damage could Helene cause in Florida?

Helene’s true toll will depend on where it lands and how other impacts, such as flooding, storm surges and tornadoes, play out. But the wind speed and category at landfall will have the most impact on power outages and structural damage.

A Wednesday forecast from the National Hurricane Center shows the storm making landfall Thursday night as a Category 3 with winds near 125 mph, just 4 mph below Category 4 strength. Meanwhile, AccuWeather forecasters predicted Helene could reach Category 4 strength in the Gulf.

If it were to hit Cat 4 power, the storm would by definition leave a trail of “catastrophic” damage. The National Hurricane Center says that Category 4 storms threaten well-built, frame homes with “severe” damage, with the loss of both roof and walls. Most trees will be snapped or uprooted, and utility poles will be toppled.

“Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months,” the hurricane center says of Category 4 storms.

A Category 3 storm, while significantly weaker, is still a major hurricane. “Electricity and water will be unavailable for several days to weeks after the storm passes,” the center says of Category 3 storms.

What is a major hurricane?

Although all hurricanes produce life-threatening winds, Category 3 and higher hurricanes are called major hurricanes. Major hurricanes can cause devastating to catastrophic wind damage and loss of life. Hurricanes of all categories can produce deadly storm surges, rain-induced flooding, and tornadoes.

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What are the 5 hurricane categories?

Category 1 Hurricane: 74-95 mph (119-153 km/h)Very dangerous winds will cause some damage: Well-built frame homes may have damage to the roof, shingles, vinyl siding, and gutters. Large tree limbs will snap and trees with shallow roots may topple. Extensive damage to power lines and poles will likely result in power outages lasting from a few to several days.

Category 2 Hurricane: 96-110 mphExtremely dangerous winds will cause extensive damage: Well-built frame homes may sustain extensive roof and siding damage. Many shallow-rooted trees will be snapped or uprooted, blocking numerous roads. Near-total power loss is likely, including blackouts that could last from days to weeks.

Category 3 Hurricane (Major): 111-129 mphDevastating damage will occur: Well-built frame homes may sustain extensive damage or have roofing and gables removed. 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 Hurricane (Severe): 130-156 mphCatastrophic damage will occur: Well-built, framed homes may sustain severe damage, losing most of the roof structure and/or some exterior walls. Most trees will be broken or uprooted, and utility poles will fall. Fallen trees and utility poles will isolate residential areas. Power outages will last for weeks or possibly months. Most of the area will be uninhabitable for weeks or months.

Category 5 Hurricane (Major): 157 mph or higherCatastrophic damage will occur: a high percentage of frame homes will be destroyed; there will be total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks or possibly months. Most of the area will be uninhabitable for weeks or months.

How often do these categories occur?

Category 1 hurricanes are the most common, with as many as seven forming each year, according to Fox Weather. By comparison, only three Category 3 hurricanes typically form each year.

The least common are the extremely rare Category 5 hurricanes, of which only four have made landfall in U.S. history, according to Weather.com.