People across the country are now watching the menacing Category 4 Hurricane Florence swirling toward the Carolinas for a possible landfall late this week, but one Boulder scientist has been studying it for 10 days. Like many, he does not like what he sees.

"I've been tracking it since it was a disturbance, when it was in the formative stages leaving the African continent," said Falko Judt, a research scientist at the National Center for Atmospheric Research in Boulder. His specialty is the intensification of hurricanes, and Florence has proved an interesting and concerning case study.

"What we saw at first is that it intensified very quickly, and that caught us by surprise. It did something that was not forecast," Judt said. "It intensified very quickly and it reached Category 4 status. And then it weakened quickly. There was a very short burst of intensification, and then it dropped again."

That temporary decrease in strength this past weekend had been caused by wind shear, the result of entering an area where currents in the upper atmosphere disrupt the system's symmetry, shifting the storm clouds within the system to one side in a lopsided manner, temporarily slowing the building strength of the storm.


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But following that weakening that occurred Sunday, as it churned across the Atlantic south of Bermuda and north of Puerto Rico, Florence regained its strength, qualifying once again as a Category 4 hurricane, meaning it has maximum sustained winds between 130 and 156 mph. Only Category 5 storms are stronger. On Tuesday it was estimated to be headed for a landfall in the Carolinas late Thursday night or into early Friday morning.

"It's a Category 4, but it's expected to intensify to high-end Category 4 tomorrow (Wednesday)," Judt said. The forecasts are calling for it to be a Category 4 (at landfall), but there is an outside chance it could get up to Category 5."

The most recent Category 5 hurricane over the Atlantic was Hurricane Maria, which devastated Dominica and Puerto Rico last September, claiming an acknowledged death toll in Puerto Rico alone of nearly 3,000 people.

"The main reason (for Florence's strength) is the warm water," Judt said, putting the surface temperature at about 29 degrees Celsius, or 88 degrees Fahrenheit. "That's 1 to 2 degrees warmer than usual, so there is more energy available for the storm

"The warmer the water, the more water evaporates, and this water vapor is the fuel for the hurricane ," he added. "The whole energy conversion, warm surface water, to clouds to hurricane, it's more efficient when there is more water vapor available."

Judt was seconded by NCAR Distinguished Senior Scientist Kevin Trenberth.

"The sea surface temperatures are well above norm, especially to the north of there," Trenberth said by email. "The ocean heat content is also substantially above normal in and around Florence. We have updated the (ocean heat content) and the season April-May-June is the hottest for the global ocean on record.

"So there is strong support for the storm taking a lot of heat out of the ocean and fueling itself — but producing prodigious rains and maintaining intensity."

Judt said he saw potential parallels to Hurricane Harvey, a Category 4 hurricane that made landfall in southeast Texas on Aug. 26, 2017. It caused more than $125 billion in damage when it stalled out over the Houston-metro area after coming ashore, unleashing at least 30 inches of rain in many locations.

As of Tuesday evening, the National Hurricane Center was warning of 15 to 25 inches of rain in areas affected by Florence, with maximum amounts of 35 inches near the storm's path over portions of the Carolinas, which could trigger "catastrophic" flash flooding.

Describing Florence's trajectory, Judt said, "It's the same thing that happened with Harvey. Harvey also went over very warm water, and the damage from Harvey was mostly from the rainfall that happened. ... It moved onto land, and then it just sat there and dumped all the moisture the storm had in one place."

He said forecasters see similar potential for Florence, and added a worry for what might happen when it does move further inland.

"Forecasters are getting really concerned, especially given that in the Carolinas, the inland mountains are very efficient in wringing out all the moisture," Judt said. "You get a lot of rain near the mountains, you get landslides. And that is definitely a concern with this storm, now."

Charlie Brennan: 303-473-1327, brennanc@dailycamera.com or twitter.com/chasbrennan