Monday, December 11, 2017
Tampa Bay Weather

Collision of sea breezes raises lightning danger in S. Florida

South Florida's easy sea breeze is a fresh afternoon lift on stale summer days, but it is an accomplice to a darker force.

Lured ashore by the atmosphere's response to uneven heating of land and ocean, the sea breeze pushes warm, moist air up, and up and up, building towering cumulus clouds whose innards roil with electrical charge.

The result: cooling afternoon showers, but also thunderstorms packing deadly lightning.

And Florida is unique nationwide because the sea breeze invades the peninsula from both coasts, sometimes colliding in the center like armies meeting in battle.

"The challenge for our day to day summer forecasting is determining where the sea breeze will be and which one will be more dominant, the Atlantic or the Gulf," said Robert Molleda, warning coordination meteorologist for the National Weather Service in Miami. "Determining which is more dominant dictates where storms will form."

That's important because Florida is the thunderstorm capital of the United States, according to the Florida Climate Center.

In a slice of the state that includes Palm Beach County, an average of 80 days per year include thunderstorm activity.

A region in the center of the state west of Lake Okeechobee has the highest number of thunderstorm days at 100 — a tally that the climate center likens to areas of the world that max out on thunderstorms, such as the Lake Victoria region of equatorial Africa and the middle of the Amazon basin.

But while those regions maintain thunderstorms all year, Florida's activity drops off sharply between fall and spring.

"The most active months are definitely June, July and August," said Julia Leo, a Palm Beach County Ocean Rescue supervisor whose lifeguards are responsible for clearing beaches when storms approach. "We can have several closings in a single day and lightning is the biggest threat, so we take it very seriously."

Pilots are keenly aware of Florida thunderstorm dynamics. Weather is the main cause of a rough ride, and South Florida's volatile rainy season can produce some of the biggest potholes in the sky.

"We are getting into the time of year when thunderstorms are active, and that's one of our biggest weather hazards in Florida," said National Weather Service meteorologist Arlena Moses. "People should be aware that there will be thunderstorms most days."

Between 2006 and 2015, 47 people were killed in Florida by lightning. That's more than twice the deaths of runner-up state Texas, which saw 20 people killed by lightning during the same time period.

This year, three Floridians, including two from Palm Beach County, have been killed by lightning. Another woman, Janika Gardner of Georgia, was killed Friday in Daytona Beach Shores when she was hit by a "random" lightning bolt.

"Some severe weather, high winds and lightning, are all very much tied to sea breeze-induced thunderstorms, so they need to be better understood," said David Zierden, state climatologist at the Florida Climate Center. "It's never easy to really detail where the bulk of the thunderstorm activity will be initiated on any given day."

Multiple research studies have examined Florida's sea breeze in an effort to better predict thunderstorms.

Zierden said the National Weather Service in Tallahassee dissected sea breeze climatology unique to the Big Bend area and classified it so forecasters have a historical perspective of when and where storms may pop up based on wind patterns.

But the basic science of sea breezes is the same in Florida regardless of the coast.

Land heats faster than water, creating a temperature difference that can be as much as 10 degrees, Molleda said. The warmer, lighter air over land rises and flows toward the sea creating areas of low pressure along the coast. The atmosphere compensates by sending in the cooler, moist sea breeze.

"It's replacing the hot air over land but in the act of replacing it's forcing it to rise," Molleda said. "So you get hot juicy air over the peninsula to rise quickly and the leading edge of the sea breeze will act as a trigger for storms."

In Palm Beach County, the Atlantic isn't the only body of water creating a breeze. Lake Okeechobee is big enough to create a temperature difference that forces a lake breeze to kick up.

The lake breeze can crash into the Atlantic sea breeze for an atmospheric combustion only Florida can create.

"It's South Florida meteorology 101, but it's really fascinating," Molleda said.

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