Hurricane Helene Will Deliver Robust Winds, Flash Flooding and Storm Surge

What Makes Hurricane Helene Such a Harmful Storm?

By Andrea Thompson

Hurricane season isn’t carried out with the Gulf Coast, it appears. One more storm, Helene, is heading for Florida a bit greater than two weeks after Francine walloped Louisiana. Helene is large—and is about to carry as much as 15 toes of storm surge within the state. It’s additionally anticipated to trigger excessive downpours effectively inland, with the very best potential for flash flooding within the southern Appalachian Mountains.

Although Helene fashioned simply after the mid-September peak of the Atlantic hurricane season, that is nonetheless prime time for storms as a result of ocean waters have loads of warmth to gas them after months of summer time solar. This hurricane continues a resurgence in storms that started with Francine in early September following weeks of comparatively little exercise. The lull got here after the season began with a bang with Hurricane Beryl, which grew to become the earliest Class 5 storm on document within the Atlantic basin.

Now Helene is barreling into the Gulf of Mexico, the place the surroundings is anticipated to be near very best for the storm to strengthen. Helene is forecast to develop into a significant hurricane earlier than it makes landfall someplace in Florida’s Massive Bend space (the criminal between the state’s panhandle and its major peninsula).

On supporting science journalism

If you happen to’re having fun with this text, think about supporting our award-winning journalism by subscribing. By buying a subscription you’re serving to to make sure the way forward for impactful tales concerning the discoveries and concepts shaping our world at this time.

One key risk from Helene can be storm surges, that are anticipated to achieve 10 to fifteen toes above floor degree within the worst-hit areas of the Massive Bend. Decrease, although nonetheless probably damaging, surge ranges are forecast as distant from the middle of the storm because the southern tip of Florida. One motive for the massive surge footprint would be the storm’s measurement, which is anticipated to be within the prime 10 p.c of hurricanes at related latitudes.

Helene can be so large partially as a result of “it’s starting out big,” says Kim Wooden, an atmospheric scientist on the College of Arizona. Additionally, the storm’s heart is at present threading the needle between Cuba and Mexico; this retains it over water, permitting the convection that powers the core of tropical programs to proceed getting gas within the type of warmth and moisture. In the meantime the winds swirling round that heart are travelling over land, the place they encounter friction—“and that moves energy and momentum around” in a manner that may enhance the dimensions of the storm, Wooden says. Lastly, when the storm strikes into the gulf, it is going to have ample moisture and warmth, and Wooden notes there may be some analysis that means that extra humid environments yield greater hurricanes. For instance, they cite Hurricane Katrina, which grew a lot greater after it emerged into the gulf than it had been earlier, when it was within the Atlantic to the east of Florida. “The Gulf of Mexico can support bigger storms,” Wooden says.

These heat, moist situations—together with comparatively little wind shear, which may disrupt a storm’s heart—are additionally anticipated to trigger Helene to steadily intensify. It’s more likely to develop into Class 3 or stronger earlier than it makes landfall. There’s a powerful probability it might endure what is named speedy intensification, which implies a storm’s sustained winds bounce by no less than 35 miles per hour in 24 hours.

Whether or not Helene does so relies upon partially on all of these exterior environmental components, in addition to the storm’s inside construction. Hurricanes that develop a closed “eye wall” of thunderstorms round their heart “eye” can use warmth extra effectively and thus develop, Wooden explains. That is one motive consultants and forecasters are watching detailed satellite tv for pc imagery that helps them view what is going on on the heart of the storm, “almost like an x-ray to see what’s going on underneath the cloud tops,” they are saying.

Helene’s winds will doubtless trigger issues unusually far inland—with tropical-storm-force winds probably reaching into northern Georgia—as a result of the storm can be transferring pretty briskly. Storms that transfer quicker after making landfall don’t lose power as rapidly, Wooden says.

Helene can even carry substantial flooding threats from heavy rains far inland. The areas most probably to be affected lengthen northward from the Gulf Coast to the southern Appalachians, the place the risk can be at its highest. That is partly as a result of that area has been enduring a drought, so the soil is dry and packed. Meaning a lot of the rain will merely run off, says Derek Eisentrout, a meteorologist on the Nationwide Climate Service’s workplace in Morristown, Tenn. Moreover, the mountainous terrain means rain can rush down slopes into lower-lying valleys, he says.

Local weather change can be enjoying a task in growing the threats from hurricanes: Rising seas add to surge quantities, and storms now produce increased rainfall totals than they did up to now. And there may be proof {that a} increased share of hurricanes are reaching the very best intensities, so storms are additionally anticipated to endure speedy strengthening due to local weather change.

Forecasters notice that anybody in Helene’s path ought to pay shut consideration to native forecasts and orders from native officers about evacuations and areas to keep away from. Wooden notes that the Nationwide Climate Service additionally has useful Hurricane Threats and Impacts Graphics, which let individuals toggle between completely different threats—resembling flooding and winds—and click on to see the standing of their particular space.

Further reporting by Meghan Bartels.