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Hurricane Dorian

  • The New York Times reports:

    As Hurricane Dorian drew near to the Abaco Islands in the northwestern Bahamas early Sunday morning, the National Hurricane Center said in a bulletin that the maximum sustained winds around the eye of the storm had reached 160- miles an hour, making it a “catastrophic” storm with “devastating winds.” 

    It is moving westward fairly slowly — 8 miles an hour — and would soon be moving over Grand Abaco. The bulletin said storm surge as much of 15 to 20 feet was possible, enough to swamp many low-lying areas of the islands, and that as much as 24 inches of rain could fall before the storm passes.

    This is pretty much a nightmare scenario. A storm originally forecast as a Category 3 or 4 has strengthened to a Category 5 in the balmy warm waters just south of The Bahamas. A weak jet stream, and unusually high temperatures of the waters have only strengthened the storm as it slowly creeps toward The States.

    The devastating wind and sustained rain is going to pummel the tropical islands before reaching Florida on September 2, Labor Day at 2am. The NWS precipitation forecast says it all:

    There will be widespread flooding, intense surf, and damaging sustained winds. As a reminder, climate change is real and it will only get worse and worse every year until we make systemic changes to roll back greenhouse emissions, and protect our only weapon in this fight — the rainforests of Earth.

    The full list of Category 5 storms (data from Wikipedia) as of August 2019:

    NameDates as a
    Category 5
    wind speeds
    “Cuba”October 19, 1924165 mph (270 km/h)
    “San Felipe II
    September 13–14, 1928160 mph (260 km/h)
    “Bahamas”September 5–6, 1932160 mph (260 km/h)
    “Cuba”November 5–8, 1932175 mph (280 km/h)
    “Cuba–Brownsville”August 30, 1933160 mph (260 km/h)
    “Tampico”September 21, 1933160 mph (260 km/h)
    “Labor Day”September 3, 1935185 mph (295 km/h)
    “New England”September 19–20, 1938160 mph (260 km/h)
    CarolSeptember 3, 1953160 mph (260 km/h)
    JanetSeptember 27–28, 1955175 mph (280 km/h)
    CarlaSeptember 11, 1961175 mph (280 km/h)
    HattieOctober 30–31, 1961160 mph (260 km/h)
    BeulahSeptember 20, 1967160 mph (260 km/h)
    CamilleAugust 16–18, 1969175 mph (280 km/h)
    EdithSeptember 9, 1971160 mph (260 km/h)
    AnitaSeptember 2, 1977175 mph (280 km/h)
    DavidAugust 30–31, 1979175 mph (280 km/h)
    AllenAugust 5–9, 1980190 mph (305 km/h)
    GilbertSeptember 13–14, 1988185 mph (295 km/h)
    HugoSeptember 15, 1989160 mph (260 km/h)
    AndrewAugust 23–24, 1992175 mph (280 km/h)
    MitchOctober 26–28, 1998180 mph (285 km/h)
    IsabelSeptember 11–14, 2003165 mph (270 km/h)
    IvanSeptember 9–14, 2004165 mph (270 km/h)
    EmilyJuly 16, 2005160 mph (260 km/h)
    KatrinaAugust 28–29, 2005175 mph (280 km/h)
    RitaSeptember 21–22, 2005180 mph (285 km/h)
    WilmaOctober 19, 2005185 mph (295 km/h)
    DeanAugust 18–21, 2007175 mph (280 km/h)
    FelixSeptember 3–4, 2007175 mph (280 km/h)
    MatthewOctober 1, 2016165 mph (270 km/h)
    IrmaSeptember 5–9, 2017180 mph (285 km/h)
    MariaSeptember 18–20, 2017175 mph (280 km/h)
    MichaelOctober 10, 2018160 mph (260 km/h)
    DorianSeptember 1, 2019175 mph (280 km/h)

    Another way to read this table — in nearly a a century of record-keeping, roughly 30% of all Category 5 hurricanes have been recorded since the New Millennium.

  • As Hurricane Dorian quickly approaches, it’s time to revisit the hurricane forecast maps. We often forget that these storms are highly complex systems, that can grow and contract and can move across hundreds of miles fairly quickly. Shouldn’t our weather projection maps communicate that complexity? Perhaps, that’s a tall order. As an primer, this was the forecast projection map for Hurricane Maria in 2017:

    The great tragedy of these sorts of maps, is they communicate a very compressed amount of uncertainty. The paths these hurricanes can take can vary wildly around small meteorological variables. They’re simple and offer a condensed overview of the uncertainty of the storm (over time) without the baggage of demystifying a map legend and fraying model paths. While the cone projection maps condenses information, the spaghetti projection map illustrates the ensemble of projections:

    Both the cone and spaghetti maps are helpful for adjacent government planning. But neither really communicate the size or intensity of the storm, and that misinterpretation can be fatal — The Time reports:

    Studies show that some people misinterpret the map as indicating the hurricane getting bigger over time. Others think it shows areas under threat. Research by Hurakan, a University of Miami team I’m a part of, suggests 40 percent of people wouldn’t feel threatened if they lived just outside of the cone.

    The NWS does publish wind projection maps. Again, we’re looking at Hurricane Maria, which easily illustrates the destructive wind speed that pummeled Puerto Rico along its path in 2017:

    It’s instrumental to look at all the projections available to you, to collectively assemble a full picture of the storm ahead. This method of forecasting multiple models (known as ensemble forecasting) isn’t new either. It’s regularly used for tornado and severe storm predictions as well.

    Further Reading: