Powerful Irma Threatens to Put South Florida Underwater, Spill Lake Okeechobee

Near category five strength Irma represents a major flood threat from storm surge and rainfall to South Florida. Due to its large size, strong winds, its movement toward shore atop rising seas, and ability to push a tall and wide-ranging surge of water over far-flung coastlines, Irma has the potential to put major cities like Miami under water. In addition, expected 10-15 inch rainfall over Lake Okeechobee threatens the integrity of an aging dike which, if overtopped, could result in severe flooding of inland communities.

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As of the 5 PM advisory from the National Hurricane Center, Irma was a top-strength category 4 hurricane packing 155 mile per hour maximum sustained winds and a minimum central pressure of 925 mb. The storm is presently tracking just north of Cuba along a westerly or west-northwest path. It is expected to turn north by Saturday, ultimately making landfall somewhere in South Florida.

Like Harvey, Irma is very moisture rich. Like Harvey, Irma is set to interact with a deep trough dipping down over the Eastern U.S. Like Harvey, Irma is tapping warmer than normal surface waters off Florida which is helping the storm to maintain a high intensity. And like Harvey we can confidently say that the record-breaking and long-lasting high intensity of Irma has been fueled by human-forced climate change — with some weather models indicating a risk that Irma could restrengthen on approach to Florida as it crosses over the 3.5 degree F warmer than normal waters of the Gulf Stream.

Unlike Harvey, Irma is expected to continue moving after making landfall. And this movement will prevent the kind of prolonged event that occurred during Harvey — with a tropical system raining out over the same region for days and days on end. That said, Irma’s extremely strong winds presently at 155 mph and what is likely to be a very powerful storm surge pose a threat to most locations along the Florida Peninsula — especially South Florida. As with other recent hurricanes like Sandy and Matthew, Irma presents an even greater threat from storm surge flooding due to higher overall ocean levels as a result of melting glaciers in places like Antarctica and Greenland. So Irma’s massive predicted surge is running in on a higher ramp than that of decades past.

(The NAM 3 kilometer model shows a very intense 896 mb storm off South Florida by 10 PM Saturday. This model forecast shows Irma strengthening to a very extreme Category 5 storm over the much warmer than normal waters of the Gulf Stream. Official forecasts from the National Hurricane Center still call for a weaker, but still strong and dangerous, Category 4 or 5 system threatening South Florida at about this time. Image source: Tropical Tidbits.)

According to the National Hurricane Center, preliminary expected storm surges range from 8-12 feet for SW Florida from Captiva to Cape Sable, 5-10 ft from Cape Sable to Boca Rato including the Florida Keys, 5-8 ft from Venice to Captiva, 3 to 6 ft from Boca Raton to the Velusia County line, and 3 to 5 ft from Anclote River to Tampa (note that both Florida coasts expect moderate to severe storm surges and that these totals are increased and expanded from the 2 PM NHC advisory).

To put these numbers in perspective, pretty much all of South Florida, including most of the city of Miami is below 10 feet above sea level. A 10 foot storm surge with breaking, wind-driven waves on top, would therefore have catastrophic impacts for this region (see graphic below). As Irma approaches, these already significant storm surge projections may rise further even as impacts from storm surge are likely to expand up the coast.

(A ten foot rise in base sea levels as could occur during Irma’s storm surge would put most of South Florida under water. Storm surge projections for this region are presently 8-12 feet and 5-10 feet. Note that storm surge impact can vary widely based on location and that changes in Irma’s projected path is likely to alter its storm surge related impacts. Image source: Climate Central.)

Though Irma has been compared with Andrew, we must note that Irma is a significantly larger storm — dwarfing the tiny but intense Andrew. As a result, Irma has the ability to deliver a lot more in the way of a powerful surge of water to both Florida coasts. And where Andrew’s damages were primarily due to extremely high winds, Irma’s damages are likely to come from both wind and water — with the potential for very severe storm surge and flood-based destruction.

In addition to the problem of Irma’s likely large and wide-ranging surge, a second issue is the fact that there’s some concern that an aging dike holding water back from communities near Lake Okeechobee might not withstand projected rainfall totals from Irma of 10-15 inches. Though not Harvey-level rainfall amounts, these rains would come in very intense bands over the course of perhaps one day. Such heavy rainfall could cause the lake to over-top the dike — resulting in severe flooding for downstream communities.

 

(Irma’s heaviest rains are expected to fall over Lake Okeechobee — adding to an already significant flood risk to South Florida. Image source: NOAA.)

The seventy year old dike is presently vulnerable not just due to its age, but also due to the fact that a construction project aimed as shoring up the dike is underway. This rebuild in progress makes the dike even more vulnerable to heavy rains and to large waves that would be stirred up on the lake by hurricane force winds. The Army Corps of Engineers has reassured the public that a dike breach is unlikely — as its most vulnerable section in the southeast has already been strengthened. Concern remains, however, that flooding from the dike could combine with a backing up of canals due to storm surge to swamp communities far inland from the coast.

(UPDATED — UPDATES TO FOLLOW)

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23 Comments

  1. eleggua

     /  September 8, 2017

    Great post, Robert. Familiar with this effort?

    Published on Mar 23, 2017

    “Text WATER to 52886, and tell Florida’s leaders to support SB10 and HB761 and to build the EAA Reservoir, which would restore the flow of fresh, clean water to the River of Grass. It’s #NowOrNeverglades

    The fragile Everglades ecosystem is at a tipping point and needs the support of the Florida legislature. This ecosystem supports 1.3 million jobs and represents $109 billion to Florida’s economy. More than 200 Everglades scientists agree that increased storage, treatment, and conveyance of water is necessary as a long-term solution.

    The EAA reservoir would capture and store Lake Okeechobee overflow to be redistributed to the south and the Everglades, after being cleaned via filtering through the ground. This would stop the damaging discharges to the St. Lucie and Caloosahatchee rivers and the choking drought occurring in the Everglades.

    65% of Florida voters approved the purchase and the U.S. Congress reaffirmed their commitment to the project in 2016. Orvis and the outdoor industry want everyone to know how precious the Everglades is and how political will can restore the Everglades, Florida Bay, and Florida’s major estuaries.”

    Reply
    • Thanks for this, eleggua. Definitely a worthy cause.

      Reply
      • eleggua

         /  September 8, 2017

        You’re welcome.

        https://gladesdeclaration.org/

        “NOW OR NEVERGLADES
        The science is settled. The money is available thanks to 75% of Florida voters who, in 2014, voted for Amendment 1. Identify and secure the land. It’s now or never.”

        “Now or Neverglades Declaration is not a formal organization, but about 20 likeminded and knowledgeable individuals and organizations who realized the problem and solution to Florida’s water disaster are apparent. This is a nonpartisan document ignoring political posturing, created from the science and providing a reasonable conclusion. The support for the declaration’s direction is staggering and growing exponentially.”

        Reply
      • eleggua

         /  September 8, 2017

        Reply
      • eleggua

         /  September 8, 2017

        Wondering, concerned, what will remain of the Everglades after Irma and possibly Jose following in its wake through there? Difficult to think about it; painful. Thinking of Wilson and island biogeography, however the Everglades isn’t an island. Can it come back from an intense scouring, along the diversity of life there now, too?

        http://www.everglades.org/flora_and_fauna

        Reply
  2. Robert in New Orleans

     /  September 8, 2017

    A comment and a question for our astute audience.
    My understanding is that after the 2004 hurricane season (when Florida was hit by 4 named storms) most if not all of the major insurance companies withdrew from the Florida market place because of the high risk involved in maintaining a presence their. So my understanding is that when it comes to named tropical windstorms the state is supposed to provide wind damage coverage for its residents. If this is true, does mean that Irma will bankrupt the state of Florida?

    Reply
    • Good question. Don’t have a qualified answer at this time. But if the state is liable, then tens to hundreds of billions of dollars in damages would be a serious budgetary issue.

      Reply
      • eleggua

         /  September 8, 2017

        ‘The Unsustainable State Of The Florida Property Insurance Market, Part I’
        Oct. 27, 2014

        https://seekingalpha.com/article/2600335-the-unsustainable-state-of-the-florida-property-insurance-market-part-i

        “Summary

        This is the first of a four-part series on the evolution of the Florida property insurance market.

        Regulation and conflicting policies have created a dysfunctional market that has distorted pricing, undermined competition and burdened taxpayers with enormous risks.

        Florida has 5% of the total U.S. population, but 50% of hurricane exposure due to political policies that subsidize coastal development to maintain “affordability”.

        History shows that periods of relative calm are punctuated by catastrophic losses that create chaos in the insurance market.”

        Reply
    • eleggua

       /  September 8, 2017

      Here you go.

      https://sites.law.lsu.edu/coast/2011/09/florida-wind-pool-exposure/

      “Florida’s current homeowner’s insurance system is broken. One major hurricane has the potential to bankrupt private insurers, and the State’s self-insurance programs, devastating Florida’s already weakened economy (Miami Herald, 21 Sept 2009).”

      Reply
      • eleggua

         /  September 8, 2017

        ^That website links to an 18-page pdf; didn’t want to post the pdf link here. If you want to read the entire thing, easy to snag from that site. The pdf’s from some agency called
        “Florida Council of Economic Advisors at Florida TaxWatch”.

        Reply
  3. miles h

     /  September 8, 2017

    i was just looking at Irma on earth.nullschool and saw that it has an astonishing energy density of 58kW/cubic metre!!…. just mind-blowing. https://earth.nullschool.net/#current/wind/isobaric/1000hPa/overlay=wind_power_density/orthographic=-71.85,15.59,345/loc=-75.317,22.566

    Reply
    • eleggua

       /  September 8, 2017

      ‘Hurricane Irma sideswipes Cuba’s northern coast’
      September 08, 2017

      http://www.miamiherald.com/news/weather/hurricane/article172020557.html

      “Waves as high as 23 feet began crashing over seawalls in eastern Cuban towns early Friday, causing widespread flooding and power outages as Hurricane Irma moved westward along Cuba’s northern coast…..

      As Irma swirled off its shores, Cuba celebrated the feast day of its patron saint, Our Lady of Charity of El Cobre. In an irony on a day when angry seas were buffeting Cuba, the small wooden statue of the Virgin Mary that would become venerated as the island’s patron saint was found bobbing in the Bay of Nipe after a violent storm in 1612. When three salt collectors fished her out, miraculously neither the statue nor the virgin’s clothing appeared to be wet.”

      Reply
  4. Godfrey

     /  September 8, 2017

    From UK. Thinking of you all IN USA and the mzny flooded znd devastated regions elsewhere. wishing everyone gets through this one safely.

    Off topic: does anyone know the wheat crop losses this year in the Dakotas. I cannot make sense of the govt figures. Thank you.

    Reply
  5. eleggua

     /  September 8, 2017

    ‘Lake Okeechobee communities resist Irma evacuation orders
    September 08, 2017

    http://www.idahostatesman.com/entertainment/article172073992.html

    “Many people in the small, impoverished communities south of Lake Okeechobee said they wouldn’t evacuate Friday, saying they either had no transportation and nowhere to go, or they chose to accept whatever fate Hurricane Irma would inflict upon them….

    The Mar-a-Lago mansion, now owned by President Donald Trump, sits 45 miles (72 kilometers) east of the lake. The 1928 hurricane damaged just one of its arched, Roman-style windows….”

    Reply
  6. eleggua

     /  September 8, 2017

    ‘Tropical Tidbit for Friday, September 8th, 2017’

    “We continue to track three hurricanes, all of them Category 3 or stronger and all of them threats to land…truly historic day and a dangerous one for many.

    ..Jose…winds of 150mph…about as healthy as it could possibly be….could come very close to Barbuda…hopefully everyone is gone (evacuated)….

    Irma…lumbering…indeed the correct because this system has become gigantic…
    closed and very healthy looking eyewall that is larger than the old one…
    pressure still under 939mb….”

    Reply
    • eleggua

       /  September 8, 2017

      “Sailin’ away on the crest of a wave
      It’s like magic
      Oh rollin’ and ridin’, slippin’ and sliding
      It’s magic “

      Reply
  7. eleggua

     /  September 8, 2017

    Aw, poor Rush; life is hard; he’s gonna miss the movie now.

    ‘Rush Limbaugh indicates he’s evacuating Palm Beach days after suggesting Hurricane Irma is fake news’
    Sept. 8, 2017

    http://www.chicagotribune.com/news/nationworld/ct-hurricane-irma-rush-limbaugh-evacuates-palm-beach-fake-news-20170908-story.html

    “I was going to go to a private movie screening this afternoon, and I had a bunch of stuff to do tonight, and now that’s all blown to smithereens.”

    Reply
  8. wharf rat

     /  September 9, 2017

    Reply

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