Hurricane Harvey is forecast to become the first "major hurricane" to make landfall on U.S. soil in 12 years. But what exactly is a "major" hurricane? And how is it there hasn't been a major hurricane landfall since 2005, when we had Hurricane Ike in 2008 and Hurricane Sandy in 2012? Weren't both of those storms major?
According to the National Hurricane Center, a major hurricane is one with peak sustained winds of at least 111 mph, or Category 3 (or higher) on the Saffir-Simpson scale, which ranges from 1 to 5. It turns out neither Ike nor Sandy met that criteria at landfall (even though both were considered major storms at some point over the ocean).
Ike was a strong Category 2 hurricane at landfall near Galveston. And Sandy was the equivalent of a Category 1 hurricane when it barged into the Jersey Shore, but wasn't even technically considered a hurricane because it was losing its tropical characteristics
In turns out that the last major hurricane to cross the U.S. coastline was Hurricane Wilma on Oct. 25, 2005. That was 4,323 days ago — the longest stretch of time that the U.S. coast has ever experienced without a major hurricane landfall. It's a span that smashes the previous record "major hurricane drought" by almost three years.
Before Wilma, other recent major hurricane landfalls on the U.S. include Rita (2005), Katrina (2005), Dennis (2005), Jeanne (2004), Ivan (2004), and Charley (2004). By the way, the last Category 5 hurricane to hit the United States was Andrew 25 years ago Thursday.
The recent dearth of "major" hurricane landfalls does not signify that U.S. has not been hit by highly destructive hurricanes since then.
The category of a storm is based solely on the maximum wind speed somewhere in the storm. It has nothing to do with the size, the flooding rainfall, the inundating storm surge, the death toll, or the economic toll.
Since Wilma in 2005, 10 Category 1 and 2 hurricanes have made landfall on the United States — many of which produced a great deal of damage and suffering:
Humberto 2007 (Category 1)
Dolly 2008 (Category 1)
Gustav 2008 (Category 2)
Ike 2008 (Category 2)
Irene 2011 (Category 1)
Isaac 2012 (Category 1)
Sandy 2012 (Category 1, although not technically a hurricane at landfall)
Arthur 2014 (Category 2)
Hermine 2016 (Category 1)
Matthew 2016 (Category 1)
Several of these are quite infamous now, and their names have been permanently retired. But they were not major hurricanes at landfall. This is why hurricane forecasters and communicators emphasize the phrase "there's more to the story than the category." Do not dismiss the risk a storm poses because it's "only" a Category 1 hurricane.
So why do forecasters even apply the major hurricane definition?
Major hurricanes are in a league of their own due to the combination of the all worst of hurricane-related hazards.
A tropical cyclone of any intensity, even a depression, can generate tremendous rainfall and cause inland flooding; Irene is a great example of that. Category 1 and 2 hurricanes can create substantial storm surges, as Ike and Sandy illustrated.
But a major hurricane includes those hazards plus powerful winds that are characterized as causing "devastating" and "catastrophic" damage, which the lower wind speeds do not.
What makes Harvey such a threat to Texas is that it is the complete package — with the triple threat of destructive winds, a devastating storm surge, and catastrophic flooding.