Hurricane Earl is growing in size and remains on track to pass close to the Cape and Islands, bringing hurricane winds to Martha’s Vineyard, Nantucket and Cape Cod, the National Hurricane Center director Bill Read said Thursday afternoon.

In a media conference call, Mr. Read said he anticipated the eye of the storm would be “huge” by the time it got here, making for a much larger area of destructive winds.

“We have a perfect track forecast. Nantucket, the Vineyard probably the eastern half of the Cape will experience hurricane-force winds on the western side of the eye wall,” he said.

Already the hurricane has a very large wind field, with storm-force winds extending 230 miles, and hurricane force winds extending out 90 miles from the center.

“And that may actually expand,” Mr. Read said.

“There’s some indication . . . that the storm may be getting ready to do an eyewall replacement cycle,” he also said.

He said eyewall replacement is a phenomenon in which the wall of cloud surrounding the hurricane’s eye gets surrounded by another rain band that eventually chokes off the inner eye wall, and the eye thus expands.

“Storms frequently do that when they reach large intensity. You end up with a larger eye, which spreads the hurricane force winds out,” he said.

Asked how close the eye of the storm was likely to come, Mr. Read said: “The eye is going to be huge by then. I wouldn’t focus on the exact center of the eye, but the eye is coming very close to Nantucket.”

At 11 a.m. Thursday the storm’s center was 300 miles south of Cape Hatteras, and packing winds of 140 miles per hour.

“It still has very good structure, [and is] moving to the north right down the track we’ve been anticipating. It’s moving rather quickly at 18 mph,” Mr. Read said.

Forecasters had a “high confidence factor” that the storm would continue down its plotted track, which is predicted to take it just east of the Cape and Islands in the middle of Friday night.

Federal Emergency Management Administrator Craig Fugate, who also took part in the conference call, warned people not to delay in preparing for the storm.

“The message is this is a day of action,” he said.

“We expect conditions along the East Coast to deteriorate rapidly tonight and tomorrow. So people should not be lulled into a false sense that this will steer away from them.

“This is a large system, with impacts well way from the center, and time will be running out for people who have not gotten ready.”