Time runs out for Florida: Hurricane Irma to bring devastating winds, storm surge
(Note: This story will be updated throughout the day Friday.)
Barely two weeks after Hurricane Harvey brought the sprawling, flood-prone city of Houston to a halt, Hurricane Irma promises to deliver a knockout blow to another region experiencing rapid growth, and plagued by what experts call hurricane amnesia.
It has been 13 years since a Category 4 hurricane hit the U.S., when Charley made landfall north of Tampa, but that storm largely spared Miami its worst winds and storm surge flooding.
In fact, lifetime residents of southern parts of Miami under the age of 25 have never experienced a major hurricane making a direct hit before, the last one being compact but devastating Hurricane Andrew, which struck in August 1992 as a compact but ferocious Category 5 storm. That storm, too, missed downtown Miami as well as Ft. Lauderdale and West Palm Beach.
While Irma's track may waver, and its intensity may fluctuate, the storm is locked in on a path that will cause massive devastation from the Florida Keys to Miami and northward to Orlando.
The National Hurricane Center (NHC) predicts that the storm will first spread tropical storm force winds, sustained at 39 miles per hour or greater, into southern Florida on Saturday, before the center of the storm itself roars ashore somewhere between the Florida Keys and Miami on Saturday night.
The storm is expected to hit as a so-called "major" hurricane, which means it will have an intensity equivalent to a Category 3, 4, or 5 storm on the Saffir-Simpson Scale. The warm waters of the Florida Strait between the U.S. and Cuba may even cause Irma to intensify prior to making landfall.
The National Weather Service forecast office in Miami is calling the storm's threat to coastal southeastern Florida as "serious" and "potentially deadly."
Eric Blake, a forecaster at the Hurricane Center, tweeted: “This hurricane is as serious as any I have seen."
“No hype, just the hard facts. Take every life saving precaution you can.”
The winds, which could exceed 100 miles per hour in the city of Miami, which is chock full of luxury high rise condo buildings, could cause "structural damage to sturdy buildings, some with complete roof and wall failures. Complete destruction of mobile homes. Damage greatly accentuated by large airborne projectiles," the National Weather Service (NWS) warned.
"Locations may be uninhabitable for weeks or months."
Storm surge is a big threat
Perhaps the biggest concern in South Florida and along the east coast of the state is the potential for a devastating and deadly storm surge. Southwest Florida, including the low-lying Florida Keys and highly vulnerable Tampa area, are at particular risk given the current track forecast.
"Locations may be uninhabitable for an extended period"
The NHC is projecting 5 feet to 10 feet of storm surge above normal tide levels throughout the Miami area. Storm surge inundation maps show the potential for more than 9 feet of water above ground level along Biscayne Bay, and in coastal areas of southwest Florida, which may experience powerful winds from the northwest and southwest. Such winds would pile waters from the Gulf of Mexico toward the low-lying shore.
The Florida Keys in particular are extremely vulnerable to storm surge flooding, and they are facing a dire threat from Irma.
The NWS in Miami issued a statement Friday morning warning of "widespread deep inundation, with storm surge flooding greatly accentuated by powerful battering waves. Structural damage to buildings, with many washing away."
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Again, the office included this ominous warning: "Locations may be uninhabitable for an extended period."
The storm is also likely to produce widespread, severe beach erosion along the Florida shoreline, all the way north into coastal Georgia and South Carolina.
Even as Irma weakens, it is likely to produce damaging storm surge in coastal Georgia and southwestern South Carolina, storm surge expert Hal Needham warned, noting that these areas are particularly prone to surge.
Hot spots of storm surge risk include areas of the Southwest Everglades and Biscayne Bay, east of Homestead, where inundation levels of greater than 9 feet are expected.
According to the Hurricane Center's 5 p.m. ET briefing, the storm surge flooding threat in southwest Florida has increased to 8 to 12 feet of inundation above ground level from Captiva to Cape Sable, if the peak surge occurs near the time of high tide.
"This is a life-threatening situation," the statement said.
According to Needham, Hurricane Donna, which struck southwest Florida in 1960 is somewhat comparable to the storm surge threat Irma presents. Based on that storm, he warns that Irma could produce storm surge heights of 15 feet in the Florida Keys, and possibly 10 feet or greater in Biscayne Bay.
The combination of high winds and storm surge is likely to take a heavy toll on Florida homes and businesses. An analysis from the real estate information company CoreLogic found an estimated 8.5 million properties in the state are at "significant risk" of wind damage from Irma, while 3.5 million properties are at potential risk of storm surge damage.
Potential for surprises
Like most landfalling hurricanes, Irma will bring surprises. It is already a record-shattering tempest, having maintained 185-mile-per-hour or greater winds longer than any other such storm on record anywhere in the world.
It may intensify or weaken slightly shortly before landfall, potentially becoming just the fifth Category 5 hurricane to make landfall in the U.S. Because of the the Florida Peninsula is so narrow, any slight wobble east or west of its projected track would significantly alter the storm's landfall location, and therefore also have ramifications for the areas of maximum storm surge and winds.
A shift west from the currently forecast path up the middle of the peninsula would spare Miami of the worst winds and surge, but put vulnerable areas of the west coast, including Fort Myers, Sarasota, and Tampa in play for more severe impacts.
A buzzsaw path up the eastern coast of Florida would confine the worst damage to the pricey enclaves of Miami Beach, Ft. Lauderdale, West Palm Beach, and all the way up to Jacksonville.
Another wild card is whether the storm makes landfall in Cuba before making a right turn towards Florida. If it does hit Cuba directly, it could weaken to a Category 3 or low-end Category 4 storm.
Irma could be the second storm in a row to deal NASA a damaging blow, after Hurricane Harvey affected the Johnson Space Center and Ellington Field, while impacting employees' homes.
On Friday morning, Hurricane Irma was undergoing an Eyewall Replacement Cycle, or ERC, in meteorological parlance. These cycles tend to occur only in the most intense storms, and involve a process whereby a secondary eyewall forms around the storm's center. The primary eyewall decays, and gives way to the secondary one, which then contracts and yields a stronger storm as a result.
These cycles can temporarily bring a storm's winds down, but they usually go back up again once they are complete. Think of it as a storm that has the hiccups or going through an internal argument of some sort -- it doesn't mean it's seriously hobbled. In fact, once it resolves the situation, it may be even stronger.
Look out, Disney to Atlanta
Hurricane Irma's track forecast takes it northward as a weakening hurricane, all the way toward Atlanta.
This would bring hurricane force winds, heavy rains, and the threat of tornadoes to Disney World in Orlando, and could also seriously impact inland Georgia.
This would be a particularly cruel scenario, since many evacuees from southern Florida have headed north to central Florida or Georgia.
Andrew Freedman is Mashable's Senior Editor for Science and Special Projects. Prior to working at Mashable, Freedman was a Senior Science writer for Climate Central. He has also worked as a reporter for Congressional Quarterly and Greenwire/E&E Daily. His writing has also appeared in the Washington Post, online at The Weather Channel, and washingtonpost.com, where he wrote a weekly climate science column for the "Capital Weather Gang" blog. He has provided commentary on climate science and policy for Sky News, CBC Radio, NPR, Al Jazeera, Sirius XM Radio, PBS NewsHour, and other national and international outlets. He holds a Masters in Climate and Society from Columbia University, and a Masters in Law and Diplomacy from The Fletcher School at Tufts University.
