Advertisement
  1. Weather

What's the science behind our daily downpours?

Almost like clockwork, a late-afternoon storm, packed with thunder and rain, rolls across St. Petersburg’s skyline last week.
Published Jun. 29, 2015

It can be like clockwork during the summer. The dark sky. The low pressure. The lightning, often too close for comfort. The rain, sheets of it, pouring from the thunderheads faster than windshield wipers can slash it away.

Storms are a ubiquitous part of life in the Tampa Bay area, one of the stormiest regions in the country. Tampa, in particular, regularly racks up more than 80 days of storms in a year, most of which hit on summer afternoons.

So why do we see so many squalls — and why during rush hour?

Blame the heat and humidity, said WTSP 10Weather meteorologist Bobby Deskins. That, and our proximity to so many bodies of water.

Especially in the summer, the Atlantic Ocean and Gulf of Mexico produce breezes. So do Tampa Bay, smaller lakes and the remnants of previous thunderstorms. All of those winds can form stormy weather on their own, but they can also hurtle across the state on a storm-producing collision course, fed by moisture in the hot air.

"You really just have a real soupy, prime atmosphere for storm development," Deskins said.

Every storm has three essential "ingredients," said National Weather Service meteorologist Dan Noah: moisture, lift and air instability. Moisture becomes rain, lift starts the air moving, and instability — pockets of hot air rising and giving off energy — allows thunderclouds to grow.

"Think of moisture as the gasoline," Noah said. "The lift is the match, and unstable air is like blowing oxygen on a fire to get it really hot."

When it gets hot, air near the surface of the Earth starts to rise, carrying water vapor with it, Noah said. But when that warm air meets the cold air several thousand feet up, it starts to cool down again — and the water condenses, forming clouds. The tops of those clouds are positively charged, and the bottom of the cloud and the ground are negatively charged.

When the condensed water gets too heavy, it falls. Rain.

If the electrical charge on the ground changes, a kind of path forms between earth and sky, and electrons stream from clouds to meet another stream from the ground. Lightning.

When lightning strikes, the air around it expands, which creates a loud shock wave. Thunder.

And during Tampa Bay summers, all of this is supercharged. It's hotter, so air rises easily, and it's more humid, so there's more moisture. Sometimes, those factors can produce storms on their own if the air is unstable enough, Deskins said.

But the driving force of most storms is sea breezes — that extra lift. That's what makes Florida unique.

"We get sea breezes on both our coasts," Noah said. "Texas also gets a sea breeze, but they just have one. We get two."

How those breezes interact varies — and so do the time and place of storms. But here's how it usually works: as it gets hotter throughout the day, the air heats up and rises. Cooler air from over the Gulf of Mexico rushes in as a sea breeze, straight toward another wind.

It's like swiping your arm through the water in a swimming pool, Noah said. The sea breeze lifts the air and the moisture in it, the same way your arm creates a wave of swirling, fast-moving water. If there are two breezes moving toward each other — if you swing your arms together — "that water goes straight up," Noah said.

Then, it comes straight back down, right over your evening commute.

Contact Emily McConville at emcconville@tampabay.com or (813) 226-3374. Follow @emmcconville.

ALSO IN THIS SECTION

  1. A pedestrian walks through deep snow after an overnight snowfall, Monday, in Marlborough, Mass. (AP Photo/Bill Sikes) BILL SIKES  |  AP
    The nor’easter could drop 10 to 20 inches of snow by Tuesday morning from Pennsylvania to Maine, forecasters said.
  2. Ebony Fisher, 26, braves the cold weather while walking to work in downtown Tampa in this 2018 photo. OCTAVIO JONES   |   Times
    The weather will drop into the low-40s and high-30s in some areas at night.
  3. Hurricane Dorian left homes in ruin in the Bahamas. FERNANDO LLANO  |  AP
    The season’s strongest storm, Hurricane Dorian, had Florida in sight but turned north before making landfall. The storm decimated the Bahamas.
  4. A woman carries an umbrella while walking in the rain in San Francisco, Tuesday. Northern California and southern Oregon residents are bracing for a 'bomb cyclone' that's expected at one of the busiest travel times of the year. (AP Photo/Jeff Chiu) JEFF CHIU  |  AP
    The system could mean disappointment for fans of the larger-than-life balloons flown at Macy’s Thanksgiving Day Parade in New York.
  5. Temperatures are expected to rise throughout the rest of the week, but a cold front should move in over the weekend bringing lows to the mid-50s. Brandon Meyer
    Temperatures should rise throughout the week, but they won’t stay that way for long.
  6. The latest advisory from the National Hurricane Center shows the storm moving toward the northeast out to sea. National Hurricane Center
    An early morning advisory shows the storm turning toward the northeast.
  7. Tropical storm Sebastien has developed in the Atlantic and now has an 80 percent chance of turning into a tropical cyclone. [National Hurricane Center] National Hurricane Center
    Forecasters with the National Weather Service do not expect the storm to threaten land.
  8. Forecasters with the National Weather Service estimate that the system has a 50-percent chance of developing into a tropical or sub-tropical depression during the next 48 hours. National Weather Service
    Forecasters with the National Weather Service expect the system to develop into a depression by mid-week.
  9. Maintainers prepare KC-135s refueling planes to be evacuated from MacDill Air Force Base in August. A new study predicts MacDill and other Florida bases will experience a sharp rise in the number of days when the heat index tops 100 degrees Fahrenheit, making it unsafe to be outside for extended periods. MONICA HERNDON  |  Tampa Bay Times
    MacDill Air Force Base is predicted to see big increases in days the heat index tops 100 degrees.
  10. An arctic blast will chill the eastern U.S. this week and send temperatures in Florida well below normal on Wednesday. National Weather Service
    Tampa Bay might not freeze this week, but we’ll get the coldest temperatures of the season so far as they dip well below normal.
Advertisement
Advertisement
Advertisement