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What Makes Storms Like Hurricane Harvey So Strong?

What makes Hurricane Harvey so uniquely strong? Does the storm represent a new norm in extreme weather?

By
Sabrina Stierwalt, PhD,
August 28, 2017
Episode #252

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Houston, the fifth most populated city in the United States, and the surrounding areas of southeast Texas are currently facing down a historic storm known as Hurricane Harvey. The National Weather Service has warned of “catastrophic flooding” and tweeted that the storm “is unprecedented and all impacts are unknown and beyond anything experienced.” More than 250 highways have been closed due to flooding and more than 2,000 calls for rescue have been made since the storm began. An estimated 76,000 people remain without power.

When asked if his relief agency was prepared to be in Houston dealing with the aftermath for months, Brock Long, the head of the Federal Emergency Management Agency (FEMA) responded, “FEMA is going to be there for years.”

What makes Hurricane Harvey so uniquely strong? Does the storm represent a new norm in extreme weather?

How are hurricanes classified?

Hurricane Harvey was classified as a Category 4 storm when it first made landfall just south of Corpus Christi, Texas. According to the National Hurricane Center, a branch of the National Oceanic and Atmospheric Administration, these categories rank the hurricane’s sustained wind speed on the Saffir-Simpson Hurricane Wind Scale. The scale of 1 to 5 also accounts for potential property damage and loss of life.

In a Category 4 storm, winds clock in at 130 to 156 miles per hour. Power outages are predicted to last weeks and “most of the area will be uninhabitable for weeks or months”. Even well-built houses are expected to sustain severe damage including the potential for the loss of its roof and exterior walls.

But the extreme nature of Hurricane Harvey, and the potential threat brought on by other intense storms like it, is due to more than wind speed. Storm surge – how much ocean levels rise due to onshore winds - and total rainfall also contribute to a hurricane’s intensity. Harvey offers up a particularly destructive combination: an already problematic, but not unheard of, storm surge of a few feet, extremely high levels of rainfall, and a stalling of the storm over a single area for several days.

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