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Hurricane Florence, which is approaching the Carolinas, is another strong storm. Hurricanes are measured by wind. This one has had recorded speeds of up to 140 miles per hour. But whenever it makes landfall, the real danger may be rain. That's what happened with Hurricane Harvey last year in Texas. NPR's Rebecca Hersher has covered that storm's devastating aftermath and now is watching the approaching storm.
REBECCA HERSHER, BYLINE: James Kossin is a climate scientist who specifically studies hurricanes, typhoons - big, scary, swirly storms. And so far, this hurricane season has been pretty quiet - until now.
JAMES KOSSIN: There's so many hurricanes going on right now; it's almost hard to keep up.
HERSHER: There's Hurricane Olivia in the Pacific, two more storms brewing off West Africa, and then, there's Hurricane Florence, which is projected to hit the East Coast later this week.
KOSSIN: This is a incredibly dangerous storm.
HERSHER: One reason it's dangerous - it's not moving very quickly.
KOSSIN: The storm could be over North Carolina and traveling incredibly slowly on the order of, you know, just a few miles per hour, even, which is getting to the kind of speeds that we saw with Harvey.
HERSHER: Last year, Hurricane Harvey stalled around Houston. It just wouldn't move for days, so it kept raining and raining - 60 inches in some places. Earlier this year, Kossin published a study that shows storms are moving more slowly around the globe. One reason may be that climate change is causing the big currents of wind that hurricanes ride on to slow down. If Florence stalls over the East Coast, it would be another example of that slowing trend. Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo., says climate change also affects another feature of Florence - it's enormous.
KEVIN TRENBERTH: We have global warming, and so, this actually makes these storms bigger and more intense.
HERSHER: How? Well, we - all of us - burn fossil fuels, produce greenhouse gases that trap heat.
TRENBERTH: And so there's more heat in the system. And so the oceans are warmer now than they've ever been, and they're going steadily upwards.
HERSHER: Warm oceans are like a steaming bath, and evaporating moisture from that bath is the fuel for storms. So hotter oceans mean bigger, wetter hurricanes. In fact, earlier this year, Trenberth and colleagues published a study that found record-high temperatures in the Gulf of Mexico, as high as 86 degrees Fahrenheit, helped make Harvey into the rain monster it became. The amount of water that evaporated up into the hurricane as it formed matched the amount that fell all over Texas. And Trenberth emphasizes that in a storm like Harvey or Florence, the most dangerous thing is rain.
TRENBERTH: People should take these warnings very seriously because the risk of flooding, in particular, in some areas is very real.
HERSHER: Kossin agrees.
KOSSIN: The freshwater flooding poses our greatest risk to life. And this idea of a - first of all, of a very strong hurricane making landfall is always going to be very, very bad news. But then, to combine that with the potential for it to sort of stall out once it gets over land - that's a very frightening prospect to think about that.
HERSHER: Rebecca Hersher, NPR News.
(SOUNDBITE OF COOPER SAMS' "ADRIFT")
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