By the middle of next week South Florida, Caribbean Islands and the Yucatan Peninsula should have an idea of whether they sit within Hurricane Irma’s sights or not.
The storm, which has winds of 110 mph, is expected to bulk up to a Category 4 in the next several days but won’t pose a potential threat to land until next week when it nears the far eastern islands of the Caribbean.
As of the 5 p.m. Saturday advisory, Irma was about 1,135 miles for the easternmost islands of the Caribbean, moving west at 15 mph.
Forecast models have bounced all around placing Irma anywhere from the Gulf of Mexico to South Carolina to Maine or just remaining far out to sea, Klotzbach said.
“Beyond five or six days it’s anybody’s guess,” he said. “There’s nothing we can say about U.S. impact other than ‘heads up, there’s something out there, pay attention.’”
“The public should have been prepared back in June, but since Irma is knocking on our doorstep here, now’s a good time to get out there and purchase your emergency supplies,” said Miguel Ascarrunz, Broward County’s emergency management director.
Forecasters are more certain about Irma’s future strength than its future path.
“The easiest call for Irma is that it’s going to be plowing through the Atlantic as a powerful hurricane for quite a few days to come,” Henson said.
But wind shear will be increasing, so Irma may not intensify beyond Category 3 strength through the Labor Day weekend, he said.
But Irma will gain fuel as it travels west toward warmer waters, Klotzbach said.
If it encounters dry air along the way, that would suppress thunderstorms which are a hurricane’s building blocks, he said. If it encounters wind shear, or change of wind direction with height, that could distort the storm’s circulation, inhibit pressure and weaken winds, Klotzbach said.
Right now it is known that a system of high pressure will steer the storm toward the west and then toward the west-southwest during the weekend. The speed of that high pressure system, which won’t become clear for a few days, will be a significant factor in determining if Irma moves toward or away from Florida.
Beyond Wednesday, the uncertainty in Irma’s track expands greatly.
Irma will be sandwiched between a strong Atlantic upper-level ridge and an autumn-like upper-level trough that will be progress across the U.S. next week, Henson said.
The southerly flow between these features is likely to funnel Irma northward at some point late next week, but it’s still too soon to tell exactly where and when that will happen, he said.
Even if Irma recurves in a northeasterly direction as storms positioned in Irma’s current vicinity frequently do, Henson said, it “could still produce high surf and swells along much of the U.S. east coast by around next weekend.”