This 'N That: Southeast Tidal Flooding; Late Tropical Storm

A car makes its way through King Tide flooding recently in South Florida.
Photo by Joe Raedle/Getty Images via Weather Underground.

The southeastern United States has had their hands full for more than a week now with so called "nuisance flooding," in which high tides have caused repeated bouts of minor flooding along the East Coast.

The cause was a combination of astronomically higher tides this time of year, an offshore storm that drove water toward shore, sinking land masses, and climate change.

These are very similar to the factors that caused the severe flooding in Venice, Italy over the past week.  

Some of the East Coast flooding was damaging, especially during the height of the offshore nor'easter a few days ago in North Carolina.

Along the Outer Banks, officials were almost ready to open main roads like North Carolina Route 12, damaged by Hurricane Dorian earlier this year, when the latest storm undid much of that work. They'll have to start over.

Down around Miami, there's not much in the way of destruction, but the tides have run above normal daily for at least a week. The land isn't sinking there, so a lot of this is climate related.

As I've said, higher tides usually come in the autumn around Miami and northeasterly winds have driven added water ashore. But before sea levels began rising decades ago, this minor, daily nuisance flooding wasn't nearly the factor it is now.

That's because these minor "sunny day floods" are just so much more frequent now.  The amount to streets and parking lots having several inches of water on them. But these repeated salt water inundations, though not deep, can eventually cause a lot of damage to buildings and infrastructure.

Remember, salt is corrosive, which is why our cars rust so easily here in Vermont. We're always driving on salted roads in the winter.

As Weather Underground's Category 6 blog notes, citing work by NOAA oceanographer and nuisance flood expert William Sweet:

"Sea level in Miami has risen about six inches in the last 25 years, according to Sweet. That's roughly twice the global average for seal leel rise since 1993 of about 3 inches as calculated by the University of Colorado Boulder - not because of subsidence, but because of shifting ocean and atmosphere patterns that are pushing more water into the coast.

TROPICAL STORM SEBASTIEN

Hurricane season in the Atlantic Ocean is coming to a close - the season officially ends November 30, but you can still get an occasional tropical storm or hurricane after that.

There is one last hurrah going on out there. Tropical Storm Sebastien formed the other day in the central Atlantic Ocean.  It's been slowly gaining strength, even though it is rather disorganized.

Forecasters think Sebastien might strengthen into a hurricane in the next couple of days as it heads northeastward over open water.  The good news is it's very unlikely to affect land.  It's awfully late in the season for a tropical storm to form where it is - far to the northeast of Puerto Rico. But it's not unheard of.

It's good that what will likely be the final sendoff to the 2019 hurricane season will be so harmless.

No Storm, But "King Tide" Floods Miami, Other Areas

King tide flooding Sunday in Coconut Grove, Florida.
Photo by Daniel Varela, Miami Herald. 

It was a beautiful, sunny but hot day in Miami Sunday.  It hasn't rained there in days and there were no storms or tropical systems anywhere near southeast Florida.

Yet high tides flooded streets and parking lots and other areas in and around Miami, despite the lack of storms.

Welcome to king tides, now made much more noticeable by climate change.

King tides are higher than normal tides that come certain times of the year during full or new moons. In recent years, due to a combination of factors, these tides are increasingly causing minor flooding up and down the East Coast. Southeast Florida is one epicenter of this phenomenon, as are places like Charleston, South Carolina and Norfolk, Virginia.

In general the Southeastern coast is prone to king tides. Not only is the sea level rising, but the land is sinking, so that's a double whammy.

These king tides are known as nuisance floods because they get in the way but don't cause much in the way of immediate damage. But salt water infiltrates aquifers, and the salt water can damage cars, foundations and other property.

On top of that, if you get flooding on a nice sunny day, imagine what would happen if a hurricane was roaring up the coast during a king tide. Combine that with a storm surge and you get real trouble.

And of course these nuisance king tide floods are getting more frequent as sea levels rise.

According to Climate Central:

"From 2005 to 2015, the median annual frequency of flooding days more than doubled along the stretch of coast from Florida to North Carolina, according to an analysis by scientists at the National Oceanic and Atmospheric Administration (NOAA). The coast between Virginia and Maine saw a median increase of 75 percent during the same period."

That specter probably also makes people think twice about living near the coast.

Another trouble with king tides is that now they're flooding neighborhoods. When the tide goes out, the water takes fertilizers from lawns, septic tank ickiness and other debris back into Biscayne Bay, increasing pollution there, notes the Miami Herald.

Volunteers on Sunday waded into the king tides Sunday to collect water samples to study how this pollution is moving and affecting coastal waters, says the Miami Herald.

The king tides are continuing today, with coastal flood advisories and statements in effect from Florida to Long Island, New York.

Here's a video of king tide flooding in Key West, Florida this past Friday. Again, notice the lack of storminess and calm winds:

https://www.climatecentral.org/news/rising-tides-near-daily-flooding-americas-shorelines-21935