Hurricane Dorian forecasting shows how models have improved since Floyd in 1999

As Hurricane Floyd yanked trees from the Bahamian sand in September 1999, knocking out electricity and phone service on the islands, Florida watched in fear. The state meteorologist, little more than a day before the Category 4 hurricane’s expected arrival, said computer models had struggled to plot its track.

“The problem with these storms,” he said, “is the dearth of information.”

Twenty years later, Hurricane Dorian swirled out of the Atlantic Ocean like Floyd’s awful twin, decimating the Bahamas and skirting the eastern coast of Florida. But unlike Floyd, which caused 2.6 million people from Florida to the Carolinas to flee their homes — then the largest peacetime evacuation in U.S. history — forecasters and emergency managers expressed more faith in their models.

“The level of forecasting, while it’s certainly not perfect, is night and day to how it was 20 years ago,” said Fox 13 Tampa Bay chief meteorologist Paul Dellegatto.

Andy Johnson, standing, and Paul Dellegatto, seated, check the paths of past hurricanes at work. Hurricane Floyd is shown on the large monitor on the left corner of the photo. [ LOPEZ, TONY | St. Petersburg Times ]

In 1999, according to National Hurricane Center data, the average forecast track error for tropical storms and hurricanes three days out was about 240 miles. Last year, it was 117 miles.

“The decisions that you would have made at three days with the confidence level we had in 1999 is now what we’re operating with as a 5-day forecast in 2019,” said private meteorologist Ryan Maue. Public forecasts didn’t even extend to five days back then.

In 1999, the spaghetti models went out to 72-hours.

Here's a sequence of maps from Hurricane Floyd.

Now, with what you learned from Twitter about weather forecasting, and the benefit of hindsight, how do you deal with this today? What's changed? pic.twitter.com/MfC49VZQrG
— Ryan Maue (@RyanMaue) September 3, 2019

That means cones of uncertainty are shrinking, year by year, and planners have better information sooner, allowing them to make more exact decisions about school closures, evacuations and emergency declarations. Fewer parents call out of work and fewer businesses close when they don’t need to.

“Because of the improved forecast, the economy takes a much smaller hit than it used to take,” said Mark Bourassa, a professor of meteorology at Florida State University.

The improvements in forecasting have several causes, including better and more data and increased computing capacity. More processing power means scientists use more complex equations, building models off advanced physics.

They harness improved resolution to account for the land beneath storms, too, said Joel Cline, a meteorologist at the National Hurricane Center.

“There would have been a lot more warnings issued for Dorian if we had the technology of 20 years ago,” said Jeff Masters, director of meteorology at Weather Underground.

Satellite image of Hurricane Floyd [ NOAA | NOAA ]

In 1999, the National Hurricane Center’s forecast called for Floyd to move up the coast of Florida without making direct landfall, but confidence was low. News stories offered the caveat that tracks could be off by 100 miles a day in advance.

Disney World closed for the first time in its history and many flights were grounded from Orlando to Miami. Hotels were fully booked in Tampa Bay, with some worried evacuees turned away.

Floyd was wider than Dorian, meaning Florida was at obvious risk of high winds even if it stayed offshore. Forecasts called for the eye to skid within 50 miles of the coast.

“It was so close that the emergency management folks just could not take the chance that they were going to be wrong, and so they evacuated most of South Florida,” said Denis Phillips, chief meteorologist at ABC Action News.

The response to Dorian was in some ways similar. Disney World closed early and the Orlando airport stopped operations, and state and local officials ordered people in multiple counties to evacuate. Officials said up to 1.5 million people may have left ahead of the storm, including tourists and part-time residents outside evacuation areas. Watches and warnings blanketed several counties.

Jerry Jarrell, director of the Hurricane Center at the time of Floyd, has watched Dorian from afar, marveling at how close it is to the 1999 storm.

“The tools are a little sharper, but the way you have to deal with the problem — the preparedness problem — is the same,” he said. "Maybe I should say a lot sharper tools.”

Jerry Jarrell, right, stands in the middle of the busy National Hurricane Center as he talks with hurricane specialist Ed Rappaport, left, in September 1999 ahead of Hurricane Floyd. [ COOKE, BILL | Associated Press ]

The forecast was not perfect, though. Last week, early tracking showed the storm sawing through the state and across Tampa Bay as soon as the weekend, prompting a run on water at local grocery stores and sandbag distribution all over Florida. Phillips said five-day forecasts have significant error margins compared to three-day, and people should be cautious about putting too much stock in early predictions.

Modeling has not improved much on intensity, either, meaning Dorian’s strengthening before it hovered over the Bahamas was somewhat surprising — similar to how Hurricane Michael grew rapidly in the Gulf of Mexico last year. Think of a storm like a car: Intensity is about how the engine works, and the track deals with where the car will go. Scientists struggle with anticipating the former.

Jennifer Collins, a professor at the University of South Florida School of Geosciences, said the growth in forecasting and people’s trust in the process were obvious when she worked on evacuation surveys along the interstate over the weekend.

“By Saturday afternoon, people were deciding just to stay put,” she said. "A lot of people have just been waiting and seeing.”

By Sunday night, Eric Blake, a specialist at the National Hurricane Center, marveled at how calm life was in Florida.

“Incredible to think there is a category 5 hurricane less than 200 miles east of me, and the threat from Dorian is judged to be low enough that there’s no warning in place for Miami,” he wrote. “We live in amazing scientific times!”

Incredible to think there is a category 5 hurricane less than 200 miles east of me, and the threat from #Dorian is judged to be low enough that there’s no warning in place for #Miami. We live in amazing scientific times! pic.twitter.com/VgX3m9kSZQ
— Eric Blake 🌀 (@EricBlake12) September 1, 2019