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Gliders Showed Forecasting Progress During Hurricane Florence

The gliders' deployment in Hurricane Florence found that subsurface temperatures were about 25 degrees Fahrenheit cooler than the ocean modeling predicted without their input. Another glider helped define the Gulf Stream.

(TNS) — Angus is a sleek, yellow underwater glider with a tough carbon fiber shell that came in handy when a shark crunched down hard on it recently.

"In this section here, there was dental material left behind," said UGA Skidaway Institute of Oceanography researcher Catherine Edwards as she showed off her $270,000 "baby" in a lab where it was being repaired. "It left shark teeth behind, or a part of one." A few years ago a sea turtle tried to mate with a glider that Edwards was using to study plankton.

Gliders' adventures with wildlife make them relatable, but it's their ability to help predict hurricane intensity that is really getting attention.

Edwards was part of a national effort last year to launch gliders as hurricanes approached and gather better data on ocean temperatures to feed into hurricane models. The help is needed because while forecasters have improved their ability to predict the paths of storms, storm intensity is something that's been tough to get right.

"You can look at the trends over 50 years in track error," Edwards said. "And that's gotten a lot better; it goes down over time. We have better forecasts, further in advance. So we've got five-day forecast now that are accurate instead of just three days. But again, that's for track. But If you look at how intensity error changes over time, it's pretty flat."

That has real life consequences for emergency managers and residents who decide to stay or evacuate based in part on the category of storm expected. Two storms from the 2018 hurricane season provide examples of how quickly storm intensity can change. Hurricane Florence was predicted to be a Category 5 storm, but it weakened significantly before making landfall in North Carolina as a Category 1 storm on September 14. On the other hand, a month later, Hurricane Michael grew from a Category 1 to a Category 5 storm in just two days and hit the Florida panhandle on October 10.

Warm water fuels hurricane intensity and cool water dials it down. Models already use sea surface temperatures supplied by satellite. But gliders like Angus provide accurate, real time information about water temperature beneath the sea surface, providing a three-dimensional picture. Gliders, which propel themselves by changing their buoyancy and center of gravity, use satellite phones to transmit recorded data when they surface. Guided remotely, their missions can last up to months.

"So the satellites are picking up the surface temperature," Edwards said. "It's a skin, it's just the surface temperature, and clouds are getting in the way. You know, when you've got hurricanes coming, you kind of don't always have a clear view of what's going on."

The gliders' deployment in Hurricane Florence found that subsurface temperatures were approximately 25 degrees Fahrenheit cooler than the ocean modeling predicted without their input. Another glider deployed ahead of the storm in collaboration with researchers at the University of South Florida helped define the edge of the Gulf Stream, an ocean feature that can also provide energy to landfalling hurricanes.

"So it's possible that the data from that glider already improved any tropical storm predictions that use ocean models and take that glider data into account, because the Gulf Stream is so important in our region," Edwards said.

Those results are attracting attention. Marshall Shepherd, director of the University of Georgia's Atmospheric Sciences Program and a regular contributor to Forbes, recently wrote about Edwards' glider research there.

"Advances in hurricane intensity forecasts will only be realized when internal heat and ocean-atmosphere exchange processes associated with the hurricane are resolved," Shepherd wrote. "These robotic gliders offer another important piece to a complex puzzle."

Edwards and her colleagues at the Southeast Coastal Ocean Observing Regional Association are making plans for the 2019 hurricane season. Funded by a $220,000 grant from the National Oceanic and Atmospheric Administration, they plan to pre-position a number of gliders in strategic locations to be ready for deployment in advance of incoming storms.

"We are preparing three gliders, one in North Carolina, one here at Skidaway and one down in Florida," she said. "And we're going to have them stashed and waiting and watching."



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