Hurricane Helen brings sturdy winds, flooding and storm surge

Why is Hurricane Helen such a harmful storm?

Andrea Thompson

Hurricane season does not seem like over on the Gulf Coast. Simply over two weeks after Francine slammed into Louisiana, one other storm, Helen, is heading towards Florida. Helen is a big storm that’s anticipated to carry as much as 15 toes of storm surge to the state. Additionally it is anticipated to carry heavy rainfall inland, with flash flooding probably within the southern Appalachians.

Helene occurred simply after the height of the Atlantic hurricane season in mid-September, however after months of summer time solar, ocean waters are nonetheless heat sufficient for storms to type at the moment of 12 months. The hurricane adopted a resurgence of storms that started with Francine in early September, adopted by a number of weeks of relative inactivity. The lull got here after the season started with Hurricane Beryl, which turned the earliest Class 5 storm on document within the Atlantic basin.

Helene is at present heading towards the Gulf of Mexico, the place situations are anticipated to be close to very best for a hurricane to accentuate. Helene is anticipated to turn out to be a serious hurricane earlier than making landfall someplace in Florida’s Large Bend area (the bend between the southern tip of the state and the peninsula).

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Considered one of Helen’s main threats is a storm surge, which is anticipated to succeed in 10 to fifteen toes above floor stage within the hardest-hit areas of the Large Bend. Decrease, however nonetheless probably damaging, storm surge ranges are anticipated within the southern tip of Florida, removed from the storm’s heart. One cause for the massive storm surge footprint is the dimensions of the storm, which is anticipated to be within the prime 10 % of hurricanes at the same latitude.

One cause Helen is so large is as a result of it is “large to begin with,” says Kim Wooden, an atmospheric scientist on the College of Arizona. And since the storm’s heart, now weaving between Cuba and Mexico, stays over the ocean, convection — the powerhouse of tropical methods — can proceed to get gasoline within the type of warmth and moisture. In the meantime, the winds swirling across the heart are shifting over land, the place they encounter friction. “That transfers vitality and momentum,” which may enhance the dimensions of the hurricane, Wooden says. Lastly, because the hurricane strikes into the Gulf of Mexico, it has loads of moisture and warmth, however Wooden factors out that there are research displaying that hurricanes develop bigger in humid environments. For example, they level to Hurricane Katrina, which grew a lot bigger after it emerged within the Gulf of Mexico than it did when it was within the Atlantic Ocean east of Florida. “The Gulf of Mexico can assist larger storms,” ​​Wooden says.

These heat, moist situations, together with comparatively little wind variability that would disrupt the storm’s heart, are anticipated to assist Helene steadily strengthen, prone to turn out to be a Class 3 or increased earlier than making landfall. Helene will possible expertise a phenomenon often called speedy intensification, which implies the storm’s sustained wind speeds will enhance by at the very least 35 mph over a 24-hour interval.

Whether or not Helene does that may rely upon the entire exterior environmental elements, in addition to some on the storm’s inner construction. Hurricanes that develop a closed “eyewall” of thunderstorms round a central “eye” can use warmth extra effectively to develop, Wooden explains. One cause consultants and forecasters are turning to detailed satellite tv for pc imagery to assist them see what is going on on within the heart of the storm is as a result of it is “like an X-ray to see what is going on on beneath the cloud tops,” they are saying.

Helen’s winds will possible trigger uncommon issues inland as a result of they’re shifting at a reasonably quick pace, probably bringing tropical storm-force winds into northern Georgia. Quick-moving storms do not lose vitality as shortly after making landfall, Wooden stated.

Helene may also carry the specter of extreme flooding from heavy rains inland. The areas prone to be hardest hit stretch from the Gulf Coast north to the southern Appalachians, the place the menace shall be best. That is partially as a result of the area is in a drought, which implies the soil is dry and compacted, which means a lot of the rain will simply run off, stated Derek Eisentraut, a meteorologist with the Nationwide Climate Service in Morristown, Tennessee. And since it is mountainous, rain may run off slopes into lower-lying valleys, he stated.

Local weather change additionally contributes to the elevated menace of hurricanes: Rising sea ranges are growing storm surges, storms are bringing extra rain than previously, and there may be proof that an growing proportion of hurricanes are reaching their full depth, so storms are anticipated to accentuate extra quickly on account of local weather change.

Forecasters say folks in Helene’s path ought to pay shut consideration to native forecasts and directions from native officers about which areas to evacuate and keep away from, and Wooden famous the Nationwide Climate Service additionally has helpful data. Hurricane threat and impact graphicyou’ll be able to toggle between totally different threats, like flooding or excessive winds, and click on to see situations in a particular space.

Extra reporting by Megan Bartels.