METEOROLOGISTS SCOUR STATE FOR POST-IRMA DATA
As Hurricane Irma settled into position along the west side of Florida, Palm Beach County breathed a premature sigh of relief.
While the area was removed from the fastest winds at Irma’s core, the behemoth hurricane’s rightfront quadrant — a roiling stew prone to tornadoes — was still within reach.
A total of 12 tornado warnings sounded in Palm Beach County during Irma’s lashing as meteorologists searched radar for signs of embedded rotating thunderstorms. In Martin and St. Lucie counties, a combined 13 warnings were issued.
“These are shallow storms, not like the tornadoes of the Great Plains that you can see for a thousand miles,” said Chris Davis, an associate director at the National Center for Atmospheric Research. “They move very fast and it’s a very complicated warning and forecast problem.”
Irma’s sustained winds at Palm Beach International Airport in West Palm Beach were measured at 67 mph — just 7 mph below hurricane strength. Gusts were measured to 91 mph, which is in the range for a Category 1 hurricane.
Sustained winds are measured as an average over 1 or 2 minutes, depending on agency. Winds reported by the National Hurricane Center advisories are based on a 1-minute average.
It wasn’t until 2012 that the Wireless Emergency Alert system began beaming attention-demanding tornado alerts to wailing smartphones,
sending nerve-rattling messages meant to save lives. Although television and NOAA weather radio would have reported the tornado alerts during Wilma in 2005, Jeanne and Frances in 2004, they might not have been as conspicuous as when they are blaring through the phone.
Whether any tornadoes actually touched down during Irma is being investigated this week by teams of National Weather Service meteorologists who started Wednesday in Naples, Everglades
City and Marco Island.
Palm Beach County is scheduled for review Friday. The teams also will document damage caused by storm surge and flooding.
Kevin Scharfenberg, a meteorologist with the NWS in Miami, said several official wind gauges failed during Irma, including at airports in Miami-Dade, Fort Lauderdale and Boca Raton.
PBIA’s gauge was one of the few that continued to transmit a signal during the storm. Scharfenberg said the high wind speeds there were partly because of location near the coast.
“There is no friction when the wind is coming in off the ocean,” he said.
A detailed National Weather Service report on Irma is expected Friday or early next week.
As of Wednesday, the Storm Prediction Center had five tornado reports in Florida, including one in Broward County near Fort Lauderdale-Hollywood International Airport.
Why hurricanes carry more tornadoes in their right front quadrant is a complicated process that needs two key ingredients — wind shear and thunderstorms, Davis said.
Wind shear, which is a change in horizontal wind speed and/or direction with height, can be tilted vertical by a thunderstorm. The reason tornadoes happen on the outskirts of hurricanes is because the cores of hurricanes have warm air aloft, which doesn’t provide the same combustible buoyancy to rising air as what occurs farther out from the center where air high in the atmosphere is cooler.
Davis said the right front quadrant is also sucking tropical air northward, providing more instability in that region of the storm.
While tornadoes might have been responsible for some of the worst damage in Palm Beach County, Davis said 66-mph sustained winds are also “really significant.”
“I think the power of that kind of wind does surprise people,” Davis said.