As Irene strengthened to a hurricane overnight, a number of Caribbean islands issued storm watches and warnings, forcing itinerary changes for Carnival Cruise Lines and Royal Caribbean ships in the area.

According to the National Hurricane Center's 11 a.m. EDT advisory, Irene is about 105 miles west-northwest of San Juan Puerto Rico -- or about 70 miles northeast of Punta Cana, Dominican Republic -- with maximum sustained wind speeds of 80 mph. The storm is expected to intensify as it skims the cost of Hispaniola and heads towards the Turks and Caicos and over the Bahamas.

As of 11 a.m. EDT, the Dominican Republic, Turks and Caicos, and southeastern Bahamas were under a hurricane warning. A hurricane watch is in effect for the central Bahamas, with tropical storm warnings still in effect for rain-battered Puerto Rico.

The ninth-named storm of the season, Irene barreled over Puerto Rico Sunday night and Monday, knocking out power to 800,000 homes. So far, the storm has forced Carnival to reroute one ship and Royal Caribbean four.

Here's what you need to know about cruise ship itinerary changes:

Royal Caribbean reversed the itinerary for Oasis of the Seas. The ship, which left Fort Lauderdale on Saturday for a week-long Western Caribbean cruise, spent Sunday at sea and will visit Cozumel on Monday, spend Tuesday at sea, call on Falmouth, Jamaica on Wednesday, and visit Labadee, the line's private peninsula on Thursday. The cruise liner is expected to return to Fort Lauderdale as scheduled on Saturday.

Oasis' sister ship, Allure of the Seas, will visit all ports originally scheduled, just in a different order. The ship will head to Nassau, Bahamas on Saturday instead of Monday. Visits to St. Thomas and St. Maarten will go as planned on Wednesday and Thursday, respectively.

Freedom of the Seas will be on a reversed itinerary. The ship, which left Port Canaveral on Sunday for a week-long Western Caribbean cruise, will call on Cozumel Tuesday, Grand Cayman Wednesday, Falmouth, Jamaica Thursday and Labadee Friday.

Royal Caribbean's Serenade of the Seas will also have a scrambled schedule. The ship, which left San Juan, Puerto Rico on Sunday, will now visit Aruba Tuesday, Curacao Wednesday, St. Kitts Friday, and St. Thomas Saturday.

Carnival Miracle, which set out from New York on an eight-night Eastern Caribbean cruise on Thursday, was forced to make a big shift in its itinerary. Rather than visiting San Juan, St. Thomas and then Grand Turk, the ship will now head to Grand Turk on Monday and Half Moon Cay on Tuesday.