'Once in a lifetime tidal event': Why Hurricane Irma drained shorelines

Add this to the list of what makes Hurricane Irma an unprecedented storm: Its strength literally changed the shape of the ocean.

Before making landfall in Florida on Sunday, the most powerful Atlantic hurricane on record sucked water inward away from shorelines, leaving bays along the Gulf Coast practically dry.

That depleted canals, grounded boats, and, in Florida's Sarasota Bay, stranded manatees in knee-high mud. Videos and photos went viral of water receding as far as the eye could see, from shorelines in the Bahamas up through Florida's west coast.

In Tampa Bay, it receded so much, dogs were able to run on places that would normally be under feet-deep water.

"#Tampa bay now an effective dog park as we wait for #irma. With @CityofTampa parks closed ahead of storm, this is the best we've got," tweeted a Tampa resident on Sunday.

But meteorologists warned the water would return after Irma's eye passed through.

"The wind direction will shift to onshore, causing water levels along the southwest coast of Florida to rapidly rise in a matter of minutes. MOVE AWAY FROM THE WATER! Life-threatening storm surge inundation of 10 to 15 feet above ground level is expected in this area," the National Weather Service in Miami warned Sunday afternoon.

Here's a look at the science behind the shorelines drained by Irma.

What caused this?

A combination of Irma's strength and positioning caused the water to recede so much, said Jamie Rhome, a storm surge specialist with the National Hurricane Center. It was essentially the opposite of a storm surge, he added.

"Storm surge is where strong winds are pushing the water towards the shore. But you can imagine that same force is pushing water away from the shoreline," Rhome said. "If the wind is blowing offshore, it blows water away from land."

The reason Irma left shorelines so bare was because as its robust low-pressure center approached places like the Bahamas on Friday and Saturday, and Tampa and the rest of the Gulf Coast on Sunday, its record-smashing strong winds were blowing from northeast to southwest — which happens to be the same position as the bay.

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Hurricane Irma spreads destruction across Florida
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Hurricane Irma spreads destruction across Florida
A man died when his pickup truck crashed into a tree in the Florida Keys during Hurricane Irma in Florida, U.S. in this handout photo obtained by Reuters September 10, 2017. Monroe County Sheriff� Department/Handout via REUTERS REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY.??
The crumbled canopy of a gas station damaged by Hurricane Irma is seen in Bonita Springs, Florida, U.S., September 10, 2017. REUTERS/Bryan Woolston
Flood water from Hurricane Irma surround a damaged mobile home in Bonita Springs, Florida, U.S., September 10, 2017. REUTERS/Bryan Woolston
The crumbled canopy of a gas station damaged by Hurricane Irma is seen in Bonita Springs, Florida, U.S., September 10, 2017. REUTERS/Bryan Woolston
A collapsed construction crane is seen in Downtown Miami as Hurricane Irma arrives at south Florida, September 10, 2017. REUTERS/Carlos Barria TPX IMAGES OF THE DAY
A local resident walks across a flooded street in downtown Miami as Hurricane Irma arrives at south Florida, U.S. September 10, 2017. REUTERS/Carlos Barria TPX IMAGES OF THE DAY
A boat rack storage facility lays destroyed after Hurricane Irma blew though Hollywood, Florida, U.S., September 10, 2017. REUTERS/Carlo Allegri
A smoke shop lays destroyed after Hurricane Irma blew though Fort Lauderdale, Florida, U.S., September 10, 2017. REUTERS/Carlo Allegri
Thomas Sanz clears a fallen branch as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Mailboxes down caused by Hurricane Irma's strong winds and rain in The Vineyards in Monarch Lakes in West Miramar Sunday afternoon, Sept. 10, 2017. As the hurricane moved north up the Gulf coast, it brought violent weather to South Florida. (Taimy Alvarez/Sun Sentinel/TNS via Getty Images)
Palm Bay officer Dustin Terkoski walks over debris from a two-story home at Palm Point Subdivision in Brevard County after a tornado touched down on Sunday, Sept. 10, 2017. (Red Huber, Orlando Sentinel/TNS via Getty Images)
Brickell Avenue in Miami, Fla. was flooded after Hurricane Irma on Sunday, Sept. 10, 2017. (Mike Stocker/Sun Sentinel/TNS via Getty Images)
The Vineyards in Monarch Lake resident Syed Ali takes pictures of down tree limbs in his neighbor's front yard after Hurricane Irma left the Miramar community, sparing it from major damage other than down trees, branches and mailboxes on Sunday, Sept. 10, 2017. 'Thank God it didn't fall on either of our houses,' said Ali. (Taimy Alvarez/Sun Sentinel/TNS via Getty Images)
Brickell Avenue in Miami, Fla. was flooded after Hurricane Irma on Sunday, Sept. 10, 2017. (Mike Stocker/Sun Sentinel/TNS via Getty Images)
Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Flooding near the Hard Rock Stadium as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Fallen trees and flooded streets from Hurricane Irma are pictured in Marco Island, Florida, U.S. in this handout photo obtained by Reuters September 10, 2017. Marco Island Police Department/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY.??
Flooding in the Brickell neighborhood as Hurricane Irma passes Miami, Florida, U.S. September 10, 2017. REUTERS/Stephen Yang
Boats are seen at a marina in Coconut Grove as Hurricane Irma arrives at south Florida, in Miami, Florida, U.S., September 10, 2017. REUTERS/Carlos Barria
Boats are seen at a marina in Coconut Grove as Hurricane Irma arrives at south Florida, in Miami, Florida, U.S., September 10, 2017. REUTERS/Carlos Barria
A partially submerged car is seen at a flooded area in Coconut Grove as Hurricane Irma arrives at south Florida, in Miami, Florida, U.S., September 10, 2017. REUTERS/Carlos Barria
Boats are seen at a marina in Coconut Grove as Hurricane Irma arrives at south Florida, in Miami, Florida, U.S., September 10, 2017. REUTERS/Carlos Barria
Palm trees blow in the winds of hurricane Irma in Bonita Springs, Florida, northeast of Naples, on September 10, 2017. Hurricane Irma regained strength to a Category 4 storm early as it began pummeling Florida and threatening landfall within hours. / AFP PHOTO / NICHOLAS KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images)
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"What is unique in this case is the shore is on a parallel track, so you have the track along the west coast of Florida," Rhome said.

The same effect wasn't seen in Harvey, which devastated parts of Texas earlier this month, because that storm went in on a perpendicular track, he said.

How rare is this?

This has happened before, most notably on Long Island, New York, during Superstorm Sandy, said Shuyi Chen, a University of Washington professor of atmospheric sciences. But it doesn't usually affect such a large area.

"This phenomenon is not unique, except it will be felt much more strongly, much more obviously, when you have a storm this size," Chen said. "In physics, this is quite clearly explained. But I'm still surprised at the scale of it."

While it looks similar to what happens when an earthquake causes water to recede before a tsunami, it's not the same thing, Chen explained.

"A tsunami is not caused by wind. That is purely dynamics," she said. "The hurricane-related water retreat is mostly caused by the winds."

NBC News meteorologist Bill Karins said the timing of the tide made it even more extreme: "This is a once in a lifetime tidal event. Before the eye made landfall, the winds were blowing so hard offshore at the exact same time of low tide. People saw low water levels that they've never seen before on the west coast of Florida," he said.

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Hurricane Irma's wrath from above
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Hurricane Irma's wrath from above
Hurricane Irma (L) and Hurricane Jose are pictured in the Atlantic Ocean in this September 7, 2017 NOAA satellite handout photo. NOAA/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY.
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma on Maho beach, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
CARIBBEAN SEA - SEPTEMBER 7: In this NOAA handout image, NOAA's GOES satellite shows Hurricane Irma as it moves towards the Florida Coast in the Caribbean Sea taken at 20:00 UTC on September 07, 2017. The state of Florida is in the track of where the hurricane may make landfall. (Photo by NOAA GOES Project via Getty Images)
TOPSHOT - An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY AND AFP PHOTO / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY AND AFP PHOTO / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
CARIBBEAN SEA - SEPTEMBER 7: In this NOAA handout image, NOAA's GOES satellite shows Hurricane Irma as it moves towards the Florida Coast in the Caribbean Sea taken at 16:15 UTC on September 07, 2017. Irma is a category 5 hurricane and will bring life-threatening wind, storm surge, and rainfall hazards to the Virgin Islands and Puerto Rico. The state of Florida is in the track of where the hurricane may make landfall. (Photo by NOAA GOES Project via Getty Images)
CARIBBEAN - AUGUST 25: In this NOAA handout image, NOAA's GOES satellite shows Hurricane Irma as it makes its way across the Atlantic Ocean in to the Caribbean -- a category 5 storm with winds as high as 185 miles per hour -- today at about 3:15 pm (eastern), September 6, 2017. (Photo by NASA/NOAA GOES Project via Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma, on the Princess Juliana International Airport and Simpson Bay Beach, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS / The erroneous mention appearing in the metadata of this photo by GERBEN VAN ES has been modified in AFP systems in the following manner: [SIMPSON BAY BEACH] instead of [MAHO BEACH. Please immediately remove the erroneous mention from all your online services and delete it from your servers. If you have been authorized by AFP to distribute it to third parties, please ensure that the same actions are carried out by them. Failure to promptly comply with these instructions will entail liability on your part for any continued or post notification usage. Therefore we thank you very much for all your attention and prompt action. We are sorry for the inconvenience this notification may cause and remain at your disposal for any further information you may require. (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma in Philipsburg, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma sowed a trail of deadly devastation through the Caribbean on Wednesday, reducing to rubble the tropical islands of Barbuda and St Martin. / AFP PHOTO / ANP / Gerben van Es / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - NO ARCHIVES - NO SALE- DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma, rampaging across the Caribbean, has produced sustained winds at 295 kilometres per hour (183 miles per hour) for more than 33 hours, making it the longest-lasting, top-intensity cyclone ever recorded, France's weather service said on September 7. / AFP PHOTO / DUTCH DEFENSE MINISTRY / GERBEN VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma in Philipsburg, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma sowed a trail of deadly devastation through the Caribbean on Wednesday, reducing to rubble the tropical islands of Barbuda and St Martin. / AFP PHOTO / ANP / Gerben van Es / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - NO ARCHIVES - NO SALE- DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
TOPSHOT - An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma in Philipsburg, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma sowed a trail of deadly devastation through the Caribbean on Wednesday, reducing to rubble the tropical islands of Barbuda and St Martin. / AFP PHOTO / ANP / Gerben van Es / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - NO ARCHIVES - NO SALE- DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
An aerial photography taken and released by the Dutch department of Defense on September 6, 2017 shows the damage of Hurricane Irma in Philipsburg, on the Dutch Caribbean island of Sint Maarten. Hurricane Irma sowed a trail of deadly devastation through the Caribbean on Wednesday, reducing to rubble the tropical islands of Barbuda and St Martin. / AFP PHOTO / ANP / Gerben VAN ES / Netherlands OUT / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT 'AFP PHOTO / DUTCH DEFENSE MINISTRY/GERBEN VAN ES' - NO MARKETING NO ADVERTISING CAMPAIGNS - NO ARCHIVES - NO SALE- DISTRIBUTED AS A SERVICE TO CLIENTS (Photo credit should read GERBEN VAN ES/AFP/Getty Images)
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Will the water return?

Yes. It already has in many of Florida's shorelines.

"In essence, once the storm has moved, the water moves back in where Irma has already passed. The westerly flow brings it back almost immediately," said Mike Schichtel, lead meteorologist for the Weather Prediction Center of the National Weather Service.

Some areas will experience a dangerously high amount of water. Rhome said there was a flash flood emergency issued for the St. Johns River in northeast Florida, for example.

"When you push that much water into a river, it gets narrowed or squeezed. It's like a funnel. It has no choice but to come out of the banks," he said.

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