Florida’s busy hurricane season hasn’t increased royal tide flooding

A hunter’s moon rises today, carrying puffy fall tides known for oozing idle in waterfront streets and parks, but maybe not this year.

Miami’s National Weather Service predicts higher than normal tides with October’s full moon, but not the coastal flooding that has so often accompanied the moon-influenced royal fall tides.

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While two new moons and the full September harvest moon have passed since the weather slump began, the “minor flood” threshold has not been crossed on the official National Oceanic and Atmospheric Administration gauge at Virginia Key, near Miami.

That doesn’t mean the most vulnerable areas haven’t seen brackish intracoastal waters pour onto the streets on sunny days, but the prolonged events, killing grass, soaking sidewalks and stalling cars that have characterized the past years have generally not materialized.

Brian McNoldy, a senior research associate at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, which monitors the Virginia Key gauge, said the highest tides predicted this fall come closer to next month’s new moon. November 4.

“So we’ll see how it goes,” he said.

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But McNoldy and NOAA oceanographer William Sweet said the lack of so-called “sunny” floods this fall is likely due to a dearth of tropical cyclones pushing waters ashore along the Atlantic coast.

“It is true that even distant hurricanes – 1000, 2000+ miles away – can generate onshore swell energy along the eastern seaboard of the United States, causing high water levels for several days,” McNoldy said. “Having these storm-induced higher water levels combined with new or full moons is what usually gets us in trouble.”

Water from the Intracoastal Waterway floods Greenwood Drive at South Flagler Drive in West Palm Beach during high tide Sunday morning October 18, 2020 after seeping into storm drains.  The flooding is the result of the annual King Tides, which began in September.  The highest annual tides occur due to the influence of the moon and the Gulf Stream, but sea level rise due to climate change has increased height and flooding.

He noted Tropical Storm Melissa and Hurricane Lorenzo, both from 2019, as systems that influenced tidal flooding. Melissa, which formed south of Nantucket near the October full moon, was small but close enough to support an already swollen fall tide. Lorenzo was a major hurricane between the United States and Africa, sending westerly pulses of water that coincided with the September new moon.

This year, Hurricane Sam was a Category 4 storm in the Atlantic from late September to early October. But by the time a new moon arrived on Oct. 6, Sam was about 700 miles south-southeast of Cape Race, Newfoundland.

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NOAA has predicted potential flooding at high tide for October 6-11.

“At least for the non-event at the start of the month, this shows that even with sea level rise, meteorological factors must generally play a key role for flooding to occur, not to mention other oceanographic factors” , said Robert Molleda, warning coordinating meteorologist at the National Weather Service in Miami. “The wind and waves were pretty light during the new moon, so we didn’t get an extra ‘weather’ boost to bring the tides to flood levels.”

West Palm Beach resident Carl Flick, who lives in a flood zone along Flagler Drive north of downtown, said his neighborhood experienced noticeable flooding this fall when a royal tide coincided with heavy rains. .

But the stand-alone flooding from the royal tide was not as severe as in the past.

“We had a 10-by-5-foot puddle centered near where the drain is,” Flick said.

Water from the Intracoastal Waterway floods Greenwood Drive at South Flagler Drive in West Palm Beach during high tide Sunday morning October 18, 2020 after seeping into storm drains.  The flooding is the result of the annual King Tides, which began in September.  The highest annual tides occur due to the influence of the moon and the Gulf Stream, but sea level rise due to climate change has increased height and flooding.

High tides are amplified during full moons as a solar and lunar alignment sandwiches the Earth, creating greater gravitational pull.

In the fall, seasonal elements contribute to high tide flooding as the water warmed in the summer expands and the Gulf Stream current slows, accumulating more water along the Florida coast. Sea level rise exacerbates annual flooding at high tide.

Molleda said it was hard to predict.

“The thing is, there’s a lot we don’t fully understand about local tide levels and the different factors that play a role or how,” he said. “We have a good idea of ​​how weather conditions influence water levels (locally generated wind waves and ocean swell), but other factors such as water temperature and currents also play a role. but are not as easy to quantify.”

A man walks through the water covering parts of the Lake Trail between Royal Palm Way and Royal Poinciana Way at high tide on September 18, 2020.

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Kimberly Miller is a veteran reporter for the Palm Beach Post, part of Florida’s USA Today network. She covers weather, climate and the environment and has a certificate in weather forecasting from Penn State. Contact Kim at [email protected]

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