Highest tides of year coming, when flooding is likely

The highest tides of the year are forecast to rise this week, flooding areas susceptible to the fall’s king tide season.

Saturday’s full moon will begin pulling at the water levels Thursday, leaving some Intracoastal streets burbling with brackish water and yards fighting off the salty invasion.

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Brian McNoldy, a senior research associate at the University of Miami Rosenstiel School of Marine and Atmospheric Science, said although these will be the highest tides of the year, their inundation may be affected by a weaker easterly breezes than what was seen in October.

“We had a healthy nudge from persistent onshore winds then,” McNoldy said.

Still, it will be a nuisance for neighborhoods where residents have to park their cars elsewhere to keep from flooding or put their garbage further from their home for pickup.

High tides are magnified in the fall because the seasonally-warmed water expands as it heats up. Also, the Gulf Stream – the current of warm water rushing north off Palm Beach County’s coast – slows down in the fall, which allows more water to pile up along Florida’s coast.

“Then there is the less obvious build up called sea level rise,” said William Sweet, a NOAA oceanographer who studies tide levels. “The extra water is rising across the globe. It’s sort of ever-present, and more often during this time of year, we are finding these fall high tides spill into communities.”

A bench off Lake Trail in Palm Beach sits surrounded after water washed in from the Intracoastal Waterway. A combination of the full moon, high tide, and sea level rise are blamed for the flooding. (Lannis Waters / The Palm Beach Post)

Sweet is in Annapolis, Md., this week at a conference about areas with historic significance that are threatened by sea level rise.

The conference, Keeping History Above Water, was held in Annapolis because of it’s multiple colonial-era sites vulnerable to tidal flooding. 

Sweet said the frequency of tidal flooding, also called “sunny-day” flooding has been increasing.

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By 2040, South Florida’s streets could experience significant tidal flooding 10 times per year, according to a 2016 study published by the American Meteorological Society.

Road flooding on Flagler Drive in West Palm Beach during a king tide.

The study, titled “In Tide’s Way: Southeast Florida’s September 2015 Sunny-Day Flood,” was released as part of a package of peer-reviewed research papers that examined global extreme weather events and their relation to climate change.

Sweet said the Sept. 27, 2015, tidal flooding in South Florida was the sixth-highest flood event measured over a 20-year period.

The five higher events occurred during hurricanes, including 2005’s Hurricane Wilma. While tidal flooding usually occurs September through November, Sweet’s research focused on the Sept. 27 date. So when he estimates that could repeat itself 10 times per year, he means at the extreme Sept. 27 level of nearly two feet above the mean high water level.

“The underlying trend is clear, and it’s growing by leaps and bounds,” Sweet said.

Intracoastal water threatens a home on Marine Way in Delray Beach during a 2015 king tide.

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