BOSTON --Gov. Deval Patrick declared a state of emergency Thursday as powerful Hurricane Earl set its sights on the Massachusetts coast.

A hurricane warning was issued earlier in the day for parts of Massachusetts, including Nantucket. Earl was expected to pass about 15 miles southeast of Nantucket, Patrick said.

"It will bring hurricane-force winds and heavy rainfall to the entire Cape and the Islands and tropical force winds and hurricane force gusts to Buzzards Bay, Plymouth and the southeastern coast -- perhaps as far north as Hull," Patrick said. "We expect strong rip currents and high seas throughout the weekend."

Patrick urged residents in low-lying areas prone to flooding to leave their homes by Friday afternoon; however, no mandatory evacuations were ordered.

"Public shelters have been designated and will be supplied. NSTAR that provides electric service for most of the affected area informs us that they have drawn extra crews and equipment from across the operating region, and as far away as Michigan and Ohio, and will preposition response teams to deal with any service interruptions," Patrick said.

Boston Mayor Tom Menino said he convened city officials to develop emergency response plans in preparation for the storm, which is expected to weaken to a Category 2 hurricane as it reaches the Boston area between late Friday morning and early Saturday.

"We have been closely monitoring Hurricane Earl and we are taking proactive steps to ensure the city is ready should we experience significant rainfall and winds," Menino said.

The mayor said the city's primary concerns are flash flooding, the loss of power and fallen trees and power lines that can cause road and traffic problems. City agencies are putting preventive measures in place where possible, focusing on areas particularly vulnerable to flooding and wind damage.

Earl weakened slightly as it moved toward the North Carolina coast about 245 miles south of Cape Hatteras on Thursday, but it was still a dangerous Category 3 storm.

A tropical storm warning was also issued Thursday for the Connecticut and Rhode Island coasts into Massachusetts. Behind Earl, Tropical Storm Fiona was about 550 miles south of Bermuda.

On Cape Cod, boaters worked to pull their vessels out of the water. First responders in Barnstable were busy loading chainsaws and generators onto emergency vehicles.

Homeowners said they are hoping that Earl doesn't get too close to the shore. If that happens, local evacuations may be necessary.

Officials from the American Red Cross Chapter for the Cape and Islands said they'll decide Thursday afternoon where shelters on the Cape will be located and when they will open. A shelter was opened on Nantucket at the high school at noon.

The Department of Conservation and Recreation is taking a number of steps to prepare for the high winds and heavy rainfall predicted this weekend as Hurricane Earl passes offshore.

"It is unfortunate that this storm is predicted for the last holiday weekend of the summer recreation season," said DCR Commissioner Richard K. Sullivan Jr. "But public safety is paramount in the Patrick-Murray administration. We hope campers, beachgoers and other park visitors will understand that the closing of campgrounds, swimming pools and beaches is meant first and foremost to keep them safe and protect them from injury due to the severe weather."

DCR plans to close a number of campgrounds on Thursday and Friday. Campers who are already at the campgrounds have been asked to leave, and those whose reservations are being canceled will be given the choice of a refund or the opportunity to rebook their reservations.

DCR also plans to close all swimming and wading pools and spray decks in the Boston area, as well as several ocean beaches. Halibut Point State Park in Rockport also will be closed on Friday.

In addition, if heavy rain, high waves or strong currents become dangerous, DCR officials may close the pools and ocean beaches on subsequent days as well.

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