(CNN) -- Hurricane Dean intensified Saturday as it muscled across the Caribbean and headed toward a dangerous rendezvous Sunday with Jamaica.
Satellite image shows Hurricane Dean's position at 9:15 a.m. ET Saturday. more photos »
The Jamaican government issued a hurricane warning late Saturday morning, meaning a hurricane is expected within 24 hours, the U.S. National Hurricane Center said.
Forecasters fear Dean will be a destructive Category 5 monster packing 155 mph winds by the time it reaches Jamaica.
Even worse could be yet to come. By Monday, as Dean nears Cancun and other tourist areas along Mexico's eastern Yucatan coast, its sustained winds could be 160 mph, with gusts approaching 200 mph -- wreaking new havoc on an area heavily damaged just two years ago by Hurricane Wilma.
At 11 a.m. ET Saturday, Dean was in open water south of Puerto Rico, 565 miles east-southeast of Kingston, Jamaica, and 210 miles south-southeast of Santo Domingo, Dominican Republic, the National Hurricane Center said.
The storm's maximum sustained winds neared 150 mph with higher gusts, putting it at Category 4 intensity. It was moving north-northwest at about 17 mph. Hurricane-force winds extend 60 miles from the center of the storm, the hurricane center said. Watch CNN meteorologist Bonnie Schneider with latest on Hurricane Dean »
The storm could force NASA to cut short the space shuttle Endeavour's flight if Dean heads toward Mission Control in Houston, Reuters reported.
NASA shortened Saturday's spacewalk and prepared for a possible Tuesday landing -- one day earlier than scheduled. Bringing Endeavour back early would allow NASA to complete the flight before Mission Control would have to be evacuated, Reuters reported.
"We'd really like to protect an option to be able to end the mission on Tuesday," mission management team chairman Leroy Cain said, according to Reuters.
Jamaicans were rushing to supermarkets to stock up on groceries, batteries and nonperishable food, said Jamaican reporter Kirk Abraham.
"There are long lines," he said. "Several persons are also at the gas station trying to get petrol, kerosene and all of that. People are taking it seriously."
The two main airlines in Jamaica -- Air Jamaica and American Airlines -- have added flights and are taking on additional passengers to accommodate those who want to leave, said Lincoln Robinson, spokesman for Prime Minister Portia Simpson Miller.
The Associated Press reported several deaths and significant damage on the islands of St. Lucia, Dominica and Martinique.
Dean is forecast to reach Category 5 strength -- the highest rating on the Saffir-Simpson scale of hurricane intensity -- later in the day Saturday, with winds of at least 151 mph, according to the NHC.
With long-range computer models showing Dean turning north after striking Mexico, officials in Texas and Louisiana launched preparations for a possible midweek landfall.
Louisiana Gov. Kathleen Blanco declared a state of emergency Friday and activated the state's emergency response center. Texas Gov. Rick Perry called Dean an imminent threat and took steps to deploy emergency responders to the coast.
"It is imperative that Texans living along the coast pay close attention to threatening weather conditions and heed the warnings of their local leaders," Perry said.
Southern Texas was still dealing with flooding caused by Tropical Depression Erin, which dumped heavy rain on the region late in the week. The storm has left six people dead and one missing, according to The Associated Press. See dramatic images as Erin soaks Texas »
Blanco, whose state was devastated by hurricanes Katrina and Rita in 2005, urged Louisianans to "be prepared for the worst and hope for the best."
Besides Jamaica, hurricane warnings were in effect for the southern Dominican Republic and southern Haiti. The Cayman Islands, west of Jamaica, were under a hurricane watch, meaning hurricane conditions were expected within 36 hours.
The northern parts of the Dominican Republic and Haiti were under a tropical storm warning, and parts of Cuba were under a tropical storm watch.
A tropical storm watch for the U.S. Virgin Islands and Puerto Rico was dropped.
The hurricane center forecast rainfall of up to 6 inches in Puerto Rico, Haiti and the Dominican Republic, which could trigger flash floods. Jamaica could receive 5 to 10 inches of rain, it said.
Emergency services were gearing up in Jamaica and in the Cayman Islands, which were devastated by Hurricane Ivan in 2004.
"I implore every resident to prepare for the hurricane," Kurt Tibbetts, head of the local government in the British overseas territory, said Friday. "Take no chances. Don't second guess."
The long-range forecast shows Dean making landfall in Mexico's Yucatan peninsula, near Cancun, on Monday, before emerging back into the Gulf of Mexico on Tuesday. See Hurricane Dean's projected route »
The storm is expected to weaken over land, but forecasters predicted it would remain at least a Category 3 storm, with winds of at least 111 mph, once it gets loose again in the Gulf.
The forecast path has the storm making landfall again late Wednesday near the Texas-Mexico border. But because of the unpredictable movements of hurricanes, forecasters cautioned that the storm could strike anywhere in the western Gulf. E-mail to a friend
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All About Hurricane Dean • National Hurricane Center
Hurricane Dean forecast update at 8 a.m. (EDT) update on August 18, 2007, courtesy of NOAA. 
The  in Miami is calling Hurricane Dean "extremely dangerous," saying that the storm is gaining strength and will likely become a  storm. The storm's winds are currently clocked at 150 mph, classifying it as a . A Category 5 hurricane means the storm has winds of over 155 mph and has the potential to cause "catastrophic" damage. 

Dean is currently moving through the eastern Caribbean, and is heading towards the Dominican Republic and Haiti. The storm is expected to hit Jamaica on Sunday, and then gain even more power as it strikes Mexico's Yucatan Peninsula on Monday.

Dean could hit the mainland of the United States on Wednesday. Therefore, officials in Texas and Louisiana are currently making major preparations.

, the Governor of Texas, said the hurricane is an "imminent threat," saying the state is preparing for its arrival. Task forces have been put on alert, and supply trucks and other resources are in position.

Governor  of Louisiana declared a state of emergency yesterday so local governments can move forward with emergency plans if necessary. However, forecasters say there is little chance of Dean moving toward Louisiana. Instead, the storm is expected to threaten Mexico or Texas.

A  has been issued for Haiti from the Haiti/Dominican Republic border to .  has opened all shelters and  has declared a "state of alert" in preparation for the storm. 

A tropical storm warning remains in effect for the U.S. and  and Puerto Rico.

At 5 a.m. EDT, the center of Hurricane Dean was about 240 miles south-southwest of San Juan, Puerto Rico, and 660 miles east-southeast of Kingston, Jamaica, and was moving west at 14 mph. However, the storm is expected to pick up speed today.

Hurricane Dean could force NASA to cut short 's flight. Mission management team chairman Leroy Cain said, "We'd really like to protect an option to be able to end the mission on Tuesday."

The ''Associated Press'' reports several deaths and significant damage on the islands of St. Lucia,  and Martinique.