In Cyclones, Water, not Wind, is the Killer

September 1, 2016

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Projected 7-day rainfall from 12Z (8:00 am EDT) Thursday, September 1, through 12Z September 8, 2016. Rainfall amounts of 5 – 10” are expected along Hermine’s path across Florida and along the Southeast U.S. coast. Image credit: NOAA/NWS Weather Prediction Center.

As a warmer atmosphere becomes wetter, good to remember that water, not wind, is the biggest cause of storm damage. One more reason why, in a climate changed world, “minor” storms can do major damage – witness Louisiana.

Marshall Shepherd in Fortune:

According to the latest National Hurricane Center public advisory, the storm famously and formerly known as “Invest 99L” has the potential to produce

storm total rainfall accumulations of 5 to 10 inches over portions of northwest Florida and southern Georgia through Friday, with possible isolated maximum amounts of 20 inches. On Friday and Saturday, Hermine is expected to produce totals of 4 to 8 inches with local amounts of 10 inches possible across portions of eastern Georgia, South Carolina, and eastern North Carolina through Saturday. These rains may cause life-threatening flash flooding.

In a 2014 Bulletin of the American Meteorological Society paper Ed Rappaport reported that over the past 50 years or so, there were approximately 2500 “direct” deaths from tropical cyclones. Roughly 90% of them were from excessive storm water (that is, about 50% from storm surge and almost 25% from flood events). His 2000 study analyzed tropical systems from 1970 to 1999 and found that approximately 50% of the deaths from Atlantic tropical cyclones or their remnants were related to rain-induced flooding. The 2014 paper is a more lengthy analysis and reveals that we must get out of the habit of saying inland freshwater flooding is the most deadly aspect of a hurricane. A more accurate statement is,

Most people die from excessive storm water

Even with Hermine the National Hurricane Center warns

There is a danger of life-threatening inundation (from storm surge) within the next 36 hours along the Gulf coast of Florida from Aripeka to Indian Pass.hermine2

One positive aspect of Sandy’s legacy and previous storms is the rapid emergence of the National Weather Service prototype Storm Surge Watch/Warning graphic. These are being issued for the first time operationally with Hermine.

It is also important to note that Rappaport and Blanchard, in 2016, published a new study on “indirect” deaths. Their review of deaths from 59 tropical cyclones over the past 50 years reveals that indirect deaths are almost as large as direct deaths. The most common forms of indirect deaths include: cardiovascular failure, vehicle accidents, loss of electricity, and evacuation.

Like many of you I will continue to watch coverage of Hermine. And while the “wind” aspect of the storm often gets top-billing and is more telegenic, keep this information about excessive water in mind. I think the recent flooding in Louisiana is a poignant reminder of water’s destructive power.

Oh, I should also note that some forecast models are trying to stall Hermine off the Northeast coast of the United States early next week which could lead to a coastal flooding and rainfall threat in that region too. It certainly looks the 99L-to-Hermine legend might continue to grow.

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One Response to “In Cyclones, Water, not Wind, is the Killer”

  1. dumboldguy Says:

    An interesting piece, and it’s surprising that it has stimulated no discussion.

    From my personal perspective, wind is a bigger problem—-my house sits at the highest point in the neighborhood, and the land slopes away in all directions, so it won’t get flooded until Noah comes by on the Ark again. On the other hand, a microburst-derecho thing about 10 years ago DID knock over two of my big trees and snap the top off another—-it had winds of 85+ mph and knocked over thousands of trees in the DC area and stripped half the leaves off those left standing—-it also knocked over a few chimneys and stripped off vinyl siding and shingles off some roofs in the neighborhood.

    When Hurricane Agnes came through NO VA in 1972, there was no wind damage to speak of, but the flooding was biblical. I think my house might withstand winds up to 95-100 mph OK, but hate to think of what flooding would do to it—-glad I’m up high and sympathize with those in range of hurricane storm surge and living on flood plains (especially those on flood plains that are now flooding regularly because of AGW after not having done so for centuries).


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