Bad timing: High tides could make Hurricane Irma’s storm surge even worse

Hurricane Irma’s projected arrival in South Florida will come with an unfortunate coincidence: some of the highest tides of the year.

That means low-lying areas — including Miami, Miami Beach, Fort Lauderdale and the Keys — will be at risk of an even more dangerous storm surge. And it will be more difficult to drain it off.

Low-lying areas could be pounded by a storm surge that could reach 10 feet, which is measured from sea level. Around the same time storm conditions are expected to deteriorate late Saturday, that water level will be peaking.

September’s tides naturally are the second highest of the year, second only to October’s king tides, and this weekend’s tides are the highest of the month.

Tidal predictions in Miami and Key Largo show high tide coming between midnight and 2 a.m. Sunday and again around midday, while the area is forecast to be under hurricane-force wind and rain. With hurricane-level conditions expected to last about 12 hours and tropical-storm level rain for longer, it is likely that naturally high tides could mean more water is dumped onshore.

In Fort Lauderdale, high tide will roll in late Sunday morning — when intense rainfall will likely still be falling.

Drainage systems are expected be absolutely overwhelmed, making it hard to flush out floodwaters. Where roads were designed so that gravity would cause water to flow down and off roads, an already-high water level could slow that process.

“If the bay is higher than the outfall, then the water just stays there until the bay goes down,” said Frank Rollason, manager of North Bay Village.

Normal heavy thunderstorms can dump enough water for it to pool on low streets in these areas. A hurricane’s storm surge during high tides will only make it worse.

“If we’re unlucky enough for Irma to come directly at us, maybe she arrives closer to low tide? We can only hope,” tweeted John Morales, a meteorologist for NBC 6 in Miami.

As far as the storm surge, you’re kind of at the mercy of the tides and when the winds come.

Ed Santamaria, Coral Gables public works director

In anticipation of the deluge, canals have been lowered by the South Florida Management District. This includes the Coral Gables Waterway.

“They’ve been lowering them in a controlled manner ahead of the storm, so that should help with drainage,” said Ed Santamaria, Coral Gables public works director. “As far as the storm surge, you’re kind of at the mercy of the tides and when the winds come.”

He added that the city also took steps to check for derelict vessels and debris in the waterways, but the real work will happen after the storm hits and they can survey the damage.

“We’ll have to see if there’s any excess sedimentation, we have to look at dredging,” Santamaria said.

As many officials have said this week, Santamaria is “hoping for the best but preparing for the worst.”

Herald staff writer Alex Harris contributed to this report.