In some ways, it was like the Florida Man of storms because it didn’t know when to stop.
Storms usually end when they run out of rain or get cold air sucked into them. But not on Wednesday, when the warm and wet Gulf Stream was close to where the storm that hit Fort Lauderdale was.
In the end, more than 25 inches (63.5 centimeters) of rain fell in six to eight hours, soaking Fort Lauderdale and making it very wet. Chris Burt, a weather historian, says that was the third most rain in a 24-hour period in a big U.S. city, after Hilo, Hawaii, in 2000, with 27 inches (68.58 centimeters), and Port Arthur, Texas, in 2017, with 26.5 inches (67.31 centimeters).
Greg Carbin, forecast branch chief at the National Oceanic and Atmospheric Administration’s Weather Prediction Center, said that it could happen in other coastal areas of the United States, but Florida has the right terrain, a lot of warm water close, and other good conditions.
Carbin said that two days before the rain, a forecaster at the Weather Prediction Center named David Roth told his coworkers that the weather looked like it did on April 25, 1979, when Fort Lauderdale got 16 inches (40.64 centimeters) of rain.
Several meteorologists said that what was parked over Fort Lauderdale on Wednesday was a supercell, which is a type of strong thunderstorm that can produce deadly tornadoes and hail and moves across the Great Plains and Mid-South in a short but fierce path of destruction.
Carbin said that a cell like that would normally “snuff itself out” in about 20 minutes or at least keep going. But in Fort Lauderdale, where Carbin was, the supercell was in a break between two different weather systems. Six to eight hours went by.
Steve Bowen, a meteorologist and chief science officer for GallagherRe, a global reinsurance broker, said, “You had this extreme warmth and moisture that was just feeding into the cell, and because it had a bit of a spin to it, it was basically acting like a vacuum and sucking all that moisture back up into the main core of the system.” “Basically, it just kept going off again and again.”
Ryan Maue, who used to be the head scientist at NOAA, said that it was important that “warm ocean air from the Gulf Stream was almost always available.”
Maue and Carbin said that a strong low pressure system with counterclockwise winds that was moving around in the warm Gulf of Mexico was also a role.
The land in Florida was a little bit cooler than the sea in the Gulf Stream, which was over 80 degrees. Add wind shear, which is when winds at high and low height are going in different directions. This helps to add some spin.
Many of these things, like the Gulf Stream’s position, are not unusual on their own. But when they came together in just the right way, it was like a never-ending cycle that made it rain so much that the National Weather Service in Miami said it was a 1 in 1,000 chance that it would happen.
Bowen said, “We continue to see more and more of these once-in-a-thousand-year” weather extremes in big towns. “Everything about what is normal is changing.”
According to physics, the air holds about 4% more moisture for every degree Fahrenheit (7% for every degree Celsius) warmer it is. But warming also makes storms stronger, which adds to the amount of water in the air, said Michael Mann, a climate scientist at the University of Pennsylvania.
And then rain comes from that water.
Meteorology professor at the University of Oklahoma, Jason Furtado, said in an email that one-day downpours have become more common and stronger over the past few decades and will continue to do so in the decades to come.
“These heavy rainstorms and rising sea levels along the Florida coast should serve as big “wake-up calls” to the people of South Florida about how dangerous climate change is for them.”
