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What was parked in Fort Lauderdale on Wednesday – which caused a lot of rainfall in the Florida city – was a supercell, a type of powerful thunderstorm that can spawn deadly tornadoes and hail on a path of violent destruction, quick but short, some meteorologists have. said.
The end result was more than 63.5 centimeters of heavy rain and flooding Fort Lauderdale within six to eight hours. That was among the three heaviest in a major US city in a 24-hour period, behind 68.5 centimeters in Hilo, Hawaii, in 2000 and 67.3 centimeters in Port Arthur, Texas, in 2017, according to weather historians. .
“For context, in a six-hour period, the amount that falls is about a 1 in 1,000 chance of happening in a given year,” said Shawn Bhatti, a meteorologist with the National Weather Service in Miami.
While that could happen elsewhere along the American coast, Florida has the right topography, plenty of warm water nearby and other favorable conditions, said Greg Carbin, chief of the forecasting branch at the National Oceanic and Atmospheric Weather Prediction Center.
Just two days before the downpour, Weather Prediction Center forecaster David Roth told his colleagues that conditions were similar to April 25, 1979, when more than 40 centimeters of rain fell on Fort Lauderdale, Carbin said.
Warm ocean air provides fuel
Normally, such cells would “die off” within 20 minutes or at least stop moving, Carbin said. But in Fort Lauderdale the supercell is in the lull between opposing weather systems, Carbin said.
“You have extreme warmth and moisture that just goes into the cell, and because it rotates a little bit, it acts like a vacuum and sucks all that moisture back into the main core of the system,” said Steve Bowen, meteorologist and chief science officer for GallagherRe, a brokerage. global reinsurance. “It just keeps reigniting itself, essentially.”
What’s important, says former NOAA chief scientist Ryan Maue, is that “the availability of warm ocean air from the Gulf Stream is essentially infinite.”
Other factors include a strong low-pressure system, with counterclockwise winds, blowing across the Gulf of Mexico, Maue and Carbin said. There is a temperature difference between the slightly cooler land of Florida and the 80-degree-plus waters of the Gulf Stream. Add to that wind shear, which is when the wind flows in the opposite direction at high altitude, helping to increase spin.
‘Normal has changed’: more rain for 1 day appears
Many of these conditions in themselves are not unusual, including the location of the Gulf Stream. But when they are combined in the right way, they act like a continuous loop.
“We continue to see more and more these thousands of years” weather extremes in major cities, Bowen said. “The whole definition of normal is changing.”
Physics says that warmer climates hold more moisture in the air, about four percent more for every degree Fahrenheit (seven percent for every degree Celsius). But warming also increases the intensity of storms that increase those moisture levels, said Pennsylvania State University climate scientist Michael Mann.
And that moisture then turns into rain.
One-day rainfall has “increased in frequency and magnitude over the past several decades and will continue to increase in the coming decades,” University of Oklahoma meteorology professor Jason Furtado said in an email. “This heavy rainfall event coupled with rising sea levels off the coast of Florida should serve as an important ‘wake-up call’ to South Floridians about the severe risks posed by climate change.”
Meanwhile, affected residents continue to clean up.
In the Edgewood neighborhood of Fort Lauderdale, Christopher Alfonso and Tony Mandico, neighbors for 50 years, said their homes are likely to be total losses.
“The storm … just poured into us for hours and hours and hours,” Alfonso said. Pointing to the crowded houses with small lawns, he said, “All this asphalt, concrete, no grass – no place to [the water] go here.”
Airlines were forced to cancel or change flights to and from Fort Lauderdale Airport, which was closed until 5 a.m. Friday. Southwest canceled about 50 as of Friday morning, and that number could grow, a spokeswoman said. The airline allows customers to rebook flights to and from Miami and Palm Beach at no additional cost, he said.
More than 650 flights were canceled at Fort Lauderdale on Thursday, according to FlightAware.
Meanwhile, Broward County schools remain closed Friday.
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