The combination of Hurricane Ian’s winds, up to 8 inches of rain in some spots and king tides could mean more flooding than usual for South Florida this week.
King tides are essentially higher high tides. They happen when the moon swings closer to the earth simultaneously with a full moon or new moon. The alignment creates greater gravitational pull on the ocean, thus larger tides.
These higher tides will happen from Tuesday to Friday in South Florida, as Hurricane Ian clears Cuba, picks up strength in the Gulf of Mexico and becomes a Category 4 storm, dumping 4 to 6 inches in our area, with pockets of up to 8 inches.
High tides in the region will crest about 10 a.m. Tuesday, happening slightly later each day, with Friday’s high tide about noon. Fort Lauderdale’s highest tide of the week will be on September 28 at 10:36 a.m., clocking in at 3.36 feet, a tad higher than last year.
Rains
The National Weather Service predicts a possible 4 to 6 inches of rain in South Florida while the king tides roll in, and warns of significant flooding rain impact for all of South Florida.
“With the king tides, we’re expecting minor flooding in coastal areas, which we normally get,” said National Weather Service meteorologist Barry Baxter on Monday morning. “But with the rainfall, it could aggravate the flooding, especially during high tide.
“The main thing is that if we get heavy rain, it might take a long time for it to drain away during high tide, because it backs up the canals,” he said.
Baxter said the rain should last through Wednesday night or Thursday morning.
The periodic bands sweeping through the area through Wednesday could produce heavy rain and wind gusts to near tropical storm force, said the National Weather Service. The rains and tides could combine for flooding as early as Tuesday morning.
“We can’t rule out higher amounts [of rain], either,” Baxter warns. “The hurricane is predicted to slow down when it gets to the Tampa area, and that will slow down feeder bands” soaking Southeast Florida even more.
Winds
Winds, which cause storm surge, can supersize king tides. Baxter says that because of the storm’s counterclockwise rotation, we’ll experience winds from the northeast and east, which will push water into coastal areas. But as the storm moves farther north Tuesday night into Wednesday, winds will shift to the south-southwest. This would, in theory, push water out away from our coast.
“Winds blow water around,” said William Sweet, an oceanographer for NOAA’s National Ocean Service. “Onshore winds can pile up water along the coast. It can push water anywhere from a few inches to a foot, depending on the strength. And of course a hurricane can change it dramatically. That might go to many feet.”
Higher water
Sweet said the seas around South Florida are naturally higher at this time of year.
“In this part of the country, in the September-October-November time period, sea levels are over a half-foot higher than in the dead of winter.”
There are several factors. He explains that warmer water takes up more volume than cool water, and right now our ocean temperatures are approaching 90 degrees. “It’s just part of thermodynamics,” he says.
Additionally, the Gulf Stream slows this time of year, and prevailing winds from the north and east pick up, slowing it even further.
The Gulf Stream, in fact, may be slowing over time.
Sweet says that the science is not settled on the issue, but that models indicate that the warming atmosphere and warming ocean temperatures, combined with increased melt from Greenland and freshwater contributions point to the Gulf Stream slowing down.
This year’s king tides will be slightly weaker than those in the coming years, Sweet says.
The moon’s wobble is on an 18-year cycle that affects king tides.
“Right now we’ve been slowly declining,” he said, “And we’ll start to pick back up in about three to four years.”
The effect of climate change
NOAA says that king tide flooding is becoming more common due to decades of sea-level rise, and that the eastern U.S. and Gulf states will see a 150% increase in king-tide flooding compared to the year 2000.
“Right now we’re about a half foot higher in places like South Florida than we were about 20 years ago due to sea-level rise, and our infrastructure is where it is,” said Sweet.
“It’s a problem that we’re facing as sea levels close the gap between infrastructure and tides of all sorts. We’re starting to see an uptick in the number of days with water in the street, water covering docks — that’s the future track we’re on.”
