Hurricane Ian poses 'moderate' flash flood risk for already water-logged Space Coast

Though its track is still in flux, Hurricane Ian could dump up to 10 inches of rain along much of the Space Coast, forecasters warn, causing flash floods and risk of tornadoes mid to late this week. 

Ian, currently over the western Caribbean Sea, is forecast to strengthen into a major hurricane as it moves into the southeast Gulf of Mexico after crossing western Cuba on Tuesday, according to the National Weather Service in Melbourne. 

Forecasters issued a hurricane watch early Monday for the west coast of Florida from north of Englewood to the Anclote River, including Tampa Bay.

"While there remains uncertainty on the exact strength and track of Ian, expect increasing coverage of showers and gusty squalls with heavy rain, along with a developing risk of tornadoes through mid to late week," forecasters said early Monday.

By Monday afternoon, The National Weather Service issued a flood watch for most of Brevard County, through late Thursday.

"Extensive street flooding and flooding of creeks and rivers are possible. Area creeks and streams are running high and could flood with more heavy rain," the weather service in Melbourne's website said in its 2:29 p.m. update.

Hurricane tracker: Updates on the path of every storm — FLORIDA TODAY

While it appears that Southwest Florida will take most of Ian's wrath, the National Hurricane Center put most of Central Florida, including Brevard, at "moderate" risk of flooding. That means there is a 40% rainfall will exceed flash flood guidance in Brevard and much of the rest of Central Florida.

Regional water mangers assure there's plenty of space to store floodwaters in the St. John River's upper basin, to prevent widespread or severe flooding from the river.

"The District is closely monitoring water levels in its water management areas and the storm forecast," Ashley Evitt, a spokeswoman with the St. Johns district, wrote in an email. "At this time, the District has sufficient capacity to handle the current forecasted rainfall."

Space Coast already water logged

But saturated soils in Brevard could set the stage for localized flooding. Heavy rain drenched the already waterlogged county the past two weeks, with many neighborhoods on and near Merritt Island receiving 8 to 10 inches of rain.

Saturday morning, orange diamond-shaped "Water On Road" signs warned West Crisafulli Road motorists of a still-flooded stretch of roadway on north Merritt Island. 

Those floods heightened fears on Saturday that the situation in north Merritt Island could get worse, prompting a run on a sandbags offered by the Brevard County Sheriff's Office, with hundreds of cars lining up in the hopes of being able to stave off the impacts of more high waters.

Much of Southwest Florida is under a storm surge watch, with up to eight-foot surge from Bonita Beach to the Tampa Bay region. But the Hurricane Center was not yet forecasting any surge in east Central Florida.

Storm surge depends on the how close a storm's center comes to the coast, and can vary significantly over short distances.

Prevailing winds drive currents that cause water either to pool up in certain areas of the Indian River Lagoon or flow elsewhere. Daily tides only influence the immediate areas near openings to the ocean, such as Sebastian Inlet.

Then there's the pull of the moon, which keeps the seasonal tides and the lagoon high.

Heavy rain in the forecast

Locally, heavy rain was expected across all of east central Florida Monday afternoon, especially along the Treasure Coast, according to the National Weather Service in Melbourne. Amounts up to four inches with isolated higher amounts may fall in areas that see repeated rounds of heavy showers and storms.

"This could cause temporary flooding of roadways and poor drainage areas," the weather services hazards outlook says. "Never attempt to drive across a water covered road, as the depth may be too great to allow your vehicle to cross safely."

Some inland flooding  is possible, the weather service said. Regional waters such as the St. Johns River will swell from Ian's rains, forecasters warn. 

Blame sewage on the rain: Multiple sewage spills in Brevard blamed on routine rains

In total, the St. Johns River Water Management District operates and maintains 12 major water control structures/spillways, 76 minor water control structures, three navigational locks, one pump station and approximately 115 miles of flood control levees that are part of the District’s and U.S. Army Corp of Engineers’ federal flood protection.  

FLORIDA TODAY created zoom-in maps below of Florida storm surge zones, based on a Surge Modeling application created for the Florida Statewide Regional Evacuation Update Study, conducted for the Florida Regional Planning Councils and Florida Division of Emergency Management.

The data was derived from National Hurricane Center Sea, Lake and Overland Surges from Hurricanes (SLOSH) model runs on all the NOAA SLOSH basins throughout Florida.

Some of the worst flooding in hurricanes can be on the lagoon side of the barrier island, which is generally lower-lying.

Most of the time, the Indian River Lagoon's water level are driven purely by seasonal ocean levels, according to hydrologists and oceanographers, with rain accounting for only about 10 percent of the change.

National Hurricane Center updates at www.nhc.noaa.gov/

Jim Waymer is an environment reporter at FLORIDA TODAY. Contact Waymer at 321-261-5903 or jwaymer@floridatoday.com. Or find him on Twitter: @JWayEnviro or on Facebook: www.facebook.com/jim.waymer

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