Imagine news reports warning of a Category 1 hurricane headed for the coast of Louisiana.
For many state residents, that designation immediately puts into mind either former Category 1 storms they’ve experienced or what they’ve been told about Category 1 storms — and in each case, the conclusion generally will be that a Category 1 isn’t really that bad.
That conclusion is wrong, experts say.
“It’s important to look at every storm, at their individual storm risks,” said Ken Graham, meteorologist-in-charge with the National Weather Service in Slidell.
Although the Saffir-Simpson scale that rates hurricanes by Categories 1 through 5 has been used for years to provide a shortcut that conveys the severity of an approaching storm, the scale only applies to wind speed.
What the Saffir-Simpson scale doesn’t do is relate the size of the storm, where it could make landfall, the amount of storm surge it could bring or how fast the storm is moving. All of these variables are crucial in understanding whether the dangers associated with the hurricane are winds, flooding from rainfall or storm surge and where those dangers are expected to occur.
Every storm is different, Graham said.
“We’re desperate to find ways to better communicate storm surge, which is our biggest threat,” Graham said.
Along Louisiana’s irregular coastline, a storm hitting one area could produce vastly different storm surge levels for communities than if the storm moves just 30 or 40 miles to the east or west, Graham said.
That kind of slight movement could mean drastic storm impacts in the bays, inlets and waterways of the coast.
One of the more recent examples was Hurricane Isaac in 2012 that slowly made its way to Louisiana as a Category 1 storm.
“Isaac was big and slow and didn’t meet with what people thought of as a Category 1 storm,” Graham said.
Because of the storm’s size and extremely slow, forward speed, the storm pushed large amounts of storm surge and poured heavy rainfall across Louisiana after making landfall Aug. 28, 2012.
According to the National Oceanic and Atmospheric Administration, above-ground-level flooding was between 10 to 17 feet in Plaquemines Parish; 8 to 12 feet in St. Bernard Parish; 4 to 8 feet in Orleans and St. Tammany parishes; 3 to 6 feet in Jefferson and Tangipahoa parishes; and 1 to 3 feet in St. John the Baptist and St. Charles parishes.
The slow-moving storm pushed storm surge up against rivers, and heavy rains coming down rivers meant that in some areas, water had nowhere to go. The result was widespread flooding in LaPlace and even a temporary shutdown of Interstate 10 through the area until waters could subside.
“(Hurricane) Isaac, a Category 1, had the eighth-biggest surge in Louisiana going back to the 1880s,” said Barry Keim, state climatologist, citing information from the Southern Climate Impacts Planning Program. “(Hurricane) Ike, a Category 2 in southeast Texas, still produced a top 20 surge in Louisiana.”
The challenge now is to get people to look at more than just a category number as a way to measure their risk. The answer may just be in repeating the message — “every storm is different.”