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Rethinking hurricane ratings, post-Isaac

For Rick Knabb, halfway through his first season as director of the National Hurricane Center, the last few weeks have underscored one of the biggest challenges of the job.

It’s not figuring out where storms will go. The center’s scientists, analyzing sophisticated computer models, have become increasingly precise at predicting tracks. Persuading the public that there is no such thing as a minor hurricane, however, remains a continuing struggle.

Hurricane Isaac offered only the latest lesson that hurricanes, or tropical storms for that matter, can’t be judged by wind speed alone.

“Historically, we’ve done a better job of conveying wind hazard than we have the water-related hazards, and we realize that and have for some time,’’ said Knabb, 44, a veteran hurricane center forecaster who returned to the center in June after two years as an on-air expert at The Weather Channel. “You have to learn from every event and we’re going to learn from Isaac.”

As a tropical storm skirting South Florida, Isaac only ruffled the hair of bar patrons on Key West’s Duval Street but it dumped a once-a-century deluge over Central Palm Beach County that left neighborhood streets looking like lakes for a week. As a massive but minimal Category 1 hurricane, it pushed the Gulf of Mexico over the roof eaves of homes in Louisiana’s low-lying Plaquemines Parish. Despite evacuation orders from emergency managers and repeated warnings from forecasters of a storm surge up to 12 feet — easily capable of topping the community’s 8 1/2-foot-high protective levee — dozens of bedraggled residents had to be rescued by boat.

In the wake of Isaac, there have been numerous calls in the media, from weather bloggers to the New York Times, for an overhaul of the familiar Saffir-Simpson scale, which ranks storms on the strength of winds alone, from Cat 1 to Cat 5.

One pointed criticism of the NHC, which occupies a bunker-like building bristling with satellite dishes and antennas at the western edge of Florida International University’s main campus in West Miami-Dade County, came from a former colleague at the Weather Channel, hurricane expert Bryan Norcross.

“The NHC’s system for disseminating the forecast is archaic and relies on the media to sort it out and get it right,” Norcross wrote in a blog post last week. The center and local National Weather Service offices produce excellent and accurate forecasts, Norcross wrote, but the torrents of information can be difficult for even trained meteorologists to digest.

Norcross said the NHC’s official advisory — posted online in an all-capital-letters format resembling an old teletype dispatch — buried the critical storm surge forecast for Isaac at the bottom of the text. He argued it should have been the headline and written in plainer language. Many media outlets were complicit in downplaying Isaac as “only a tropical storm,’’ wrote Norcross, who gained national fame as a Miami television weather forecaster during Hurricane Andrew in 1992.

“The message for Plaquemines Parish should have been, “Listen, if the forecast is right, the Gulf is coming over that levee and the water will up to your roof. Now get the hell out!’’

Knabb, in an interview before flying to the Gulf Coast for post-Isaac briefings with regional emergency managers and forecasters, agreed the center needs to do a better job of explaining all the threats posed by an approaching hurricane — not just wind but tornadoes, flooding rains and especially storm surge, which has historically killed the most people.

Before he took over as director in June, the center was already experimenting with a new storm surge warning and maps intended to show potential inundation levels above ground level. Isaac, Knabb said, has given forecasters motivation to expand the testing.

Surge forecasts pose significant complexities, with the size, speed and approach angle of the storm factoring in with an array of local conditions —the timing of tides, the depth of coastal waters, the shape of the coast line, even the contour of the sea bottom. The main challenge now, said Knabb, is to quickly produce analyses and easy-to-understand maps.

While Knabb said the center welcomes feedback to improve future warnings, he also strongly defended its work on Isaac. Those complicated official advisories, for instance, are written to serve a broad array of users, from shipping interests to the military and local TV weathercasters, and are just one way information is delivered to the public.

In the days before Isaac approached South Florida and the Gulf Coast, Knabb was leading daily briefings with federal, state and local emergency managers, and he and other forecasters were regular faces on national and local news broadcasts. The NHC also was pumping out regular social media updates in more digestible nuggets on Facebook and Twitter. In all of it, the repeated message to the Gulf Coast was to worry more about water than wind.

Knabb acknowledges Isaac was a challenging storm for forecasters — a sprawling but poorly organized system that danced at the threshold of hurricane strength for much of its long journey across the Caribbean and into the Gulf of Mexico. Because it never developed a tight center core, computer models also spit out widely varying tracks for a storm with eerie timing, approaching South Florida just after the 20th anniversary of Andrew and Louisiana just before the seventh anniversary of Hurricane Katrina.

In the end, Knabb said, the center’s team of forecasters generally nailed Isaac’s track. Forecasters admittedly struggle with intensity predictions and Isaac was no exception, remaining on the low side of wind speed estimates. The center’s hurricane watches and warnings reflected that, with only the Keys falling under a hurricane warning as the storm’s core passed just south of Key West — but there was also a prediction of heavy rains, with up to a foot in some spots.

Still, there was grousing from the Keys that the storm had been overhyped, quickly followed by shock at what a brute Isaac became in Palm Beach County and Louisiana.

Knabb, who spent eight years as a senior hurricane specialist and science and operations officer at the National Hurricane Center and two years as deputy director of the Pacific Hurricane Center in Honolulu, calls that typical.

“After every storm, there are folks who express that what happens isn’t what they expected,” he said. “They either didn’t get it as bad as they expected or they got it worse.”

It seems especially pronounced for so-called minimal hurricanes below Category 3 “major” storm with winds of 111 mph or more.

Hurricane Ike in 2008, a huge Category 2 hurricane, surprised Texas when it flooded much of the coast and inundated Galveston. The storm wound up killing 112 people in the U.S. and doing nearly $30 billion in damage, making it the second-costliest hurricane in U.S. history. Last year, Category 1 Hurricane Irene caused some $7 billion in damage, most of it in New England states unprepared for torrential rains and flooding.

Knabb hopes to reduce the shock level in the future by expanding and improving the center’s communication skills.

After two years at the Weather Channel, he honed his skills at getting his message across on television, learning to project above his normal soft-spoken voice and to rein in jargon.

“I think of myself talking to a friend or family member,’’ he said. “They know I know the science but that’s not what they want or need to know.”

Bill Read, Knabb’s predecessor, was the first hurricane center director to use Twitter but Knabb has embraced it in an experimental run, tweeting up to 20 messages a day as Isaac skirted South Florida. As of Friday, he had accumulated 12,657 followers and the next storm to near the mainland United States will almost certainly add to the total.

Separate warnings from storm surge, tornadoes and flooding might help the public better prepare for storms. But after decades of study by social scientists and emergency managers, it remains baffling why some chunk of a population in the danger zone invariably rejects evacuation orders — no matter what category of hurricane threatens.

Post-storm surveys after Andrew, a catastrophic Category 5 hurricane, suggest nearly 30 percent of residents in Miami-Dade County refused to leave the most vulnerable coastal areas. Knabb believes past experience plays some role, with residents figuring that if they did well in one storm, they’ll be fine in another one. But each storm is different, bringing with it a different mix of trouble,

Consistent messages from NHC forecasters, the media and emergency managers are critical to getting people to move to safety, Knabb said, but persuading some people to seek safer shelter is “so much more complicated than any of us actually want to admit.”

“Does the number of feet of surge we’re saying tip the scale and get them to go? Does the category of storm make them go? Does the TV meteorologist get them to go? It’s not a simple answer,” he said. “I think that is what everyone is searching for after the fact. What is it that people are not hearing?’’