Computers Puzzled About Isaac’s Likely Path

Tropical Storm Isaac arrived in the Florida Keys Sunday afternoon with winds as high as 70 mph (112 kph) at Key West, Florida. This photo shows the effects of Isaac's winds and heavy rainfall at the historic Seven-Mile Bridge near Marathon, about 50 miles east-northeast of Key West. The bridge, built in the early 20th century, has withstood many powerful storms. It is no longer open to traffic. (Photo by Jeff Pinkus)


Meteorologists trying to forecast the path of Tropical Storm Isaac are puzzled because the computer programs they use to predict where a storm will go are giving them very different results.

Keith Blackwell, a meteorologist at the University of South Alabama’s Coastal Weather Research Center in Mobile, said the disgreement between hurricane forecasting programs — known as “models” — was very unusual.

The models are being fed the same data, but are producing divergent paths. One model is predicting Isaac will make landfall somewhere between the Florida Panhandle and Mississippi, while the other model is forecasting a landfall in Mississippi or Louisiana, Blackwell said.

“Based on my experience, this is a pretty serious divergence,” he said. “It’s usually somewhat better.”

The problem may be caused by the way the models are processing the influence of a weather system moving through the Midwest. The system is likely to influence where Isaac eventually comes ashore.

Blackwell said he has “no idea” why the models are producing such different results with the same data.

“I’m sure there will be some research done on this,” he said. “This is such a big quandary, and the stakes are so high.”

Isaac was gaining strength as it passed near Key West, Florida around 4 p.m. today. Blackwell said gusts of about 70 mph (112 kph) had been reported in Key West. Forecasters think Isaac will become a hurricane as it moves across the Gulf of Mexico tonight.

“It looks like this thing is on its way to beginning to crank up,” Blackwell said.

Residents in the Florida Keys started preparing for Isaac’s arrival late last week, when forecasters thought the storm might cross the low-lying islands near Marathon, the second-largest city in the Keys. Marathon resident and former mayor Jeff Pinkus said Isaac’s arrival today had not been as fierce as was feared.

“I don’t think we had winds over 40 knots (about 46 mph, or 74 kph),” Pinkus said.

Isaac is expected to continue strengthening during its trek across across the Gulf of Mexico, and Blackwell said there is still a possibility that the storm could become a major hurricane with winds exceeding 110 mph (177 kph).

Willie Drye has been writing about hurricanes and other topics for National Geographic News since 2003. Read more about Tropical Storm Isaac on his blog, Drye Goods.

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Willie Drye is an award-winning author and a contributing editor for National Geographic News. He and his wife live in Wilmington, North Carolina.