(CNN) -- Officials in some Gulf Coast states spent the third anniversary of Hurricane Katrina on Friday gearing up for what could be the biggest threat to the region since Katrina hit in 2005.

Hurricane Gustav is poised to pass near or over the Cayman Islands on Friday night and over western portions of Cuba on Saturday. It may approach the U.S. Gulf Coast by Tuesday morning as a Category 2 or 3 hurricane, the National Hurricane Center said Friday.

"Today, on that third anniversary, we've got to be thinking about the future," Mississippi Gov. Haley Barbour said. "As we pray for the best, we're going to prepare for the worst,"

Barbour announced Friday that Hurricane Katrina victims living in government-issued trailers or mobile homes along his state's coast will begin evacuating this weekend to prepare for the Gustav's possible arrival.

The process will begin Saturday, with notices going out to people living in Federal Emergency Management Agency trailers or mobile homes, as well as people living in more permanent structures known as "Mississippi cottages," he said.

The evacuation will begin in Harrison and Hancock counties on Sunday morning, Barbour said. Evacuation in Jackson County will begin Monday.

About 4,300 families live in FEMA trailers or mobile homes, and 2,800 live in Mississippi cottages, the governor's office said. He said he would urge people living in privately owned mobile homes to evacuate as well.

President Bush declared an emergency in Louisiana on Friday, freeing up federal aid and allowing FEMA to coordinate relief efforts.

Louisiana Gov. Bobby Jindal has declared a state of emergency and urged residents to update their evacuation plans.

He said residents in certain southern parishes could be asked to leave Friday or Saturday. In Plaquemines Parish, where Hurricane Katrina roared ashore as a Category 3 storm days after its initial landfall in Florida, Parish President Billy Nungesser called for a mandatory evacuation beginning at noon Saturday.

Residents of the community of Grand Isle in Jefferson Parish were urged to begin voluntary evacuations Friday afternoon, and voluntary evacuations for Jean Lafitte, Crown Point, Barataria and areas outside the levee protection system are recommended beginning at noon Saturday, the parish said in a news release.

St. Bernard Parish, which was beginning transport Friday for those who would need assistance, said it expected to call a mandatory evacuation Saturday afternoon.

In New Orleans, which has yet to fully recover from Hurricane Katrina, Mayor Ray Nagin on Thursday urged residents living in FEMA units to make evacuation plans in case city officials order them to leave.

"Travel trailers are unsafe during heavy winds," he said. "As we continue to monitor and prepare for the possibility of Hurricane Gustav, I want all of our citizens to make certain they have a plan for leaving the trailers when advised to do so."

As of early this week, there were 2,829 FEMA trailers in Orleans Parish, the mayor's office said.

The city has designated 17 sites for people without transportation to board buses that would take them out of the city in the event of a mandatory evacuation. The city also arranged with Amtrak for more than 7,000 seats to evacuate the elderly by train, said Jerry Sneed of City Homeland Security and Emergency Preparedness.

Signs of mobilization were apparent at Louis Armstrong New Orleans International Airport, where nearly every departure gate had long lines of elderly people in wheelchairs. Rental car counters normally attended by tourists were filled with relief workers from the Red Cross and the Fire Department of New York's Disaster Assistance Response Team.

The DART team consisted of retired New York firefighters, jovial men with graying hair and larger waistlines. Many are volunteers assisting the Red Cross who were in New York during the September 11 attacks and wanted to give back.

The 40-member DART team of heavy-equipment operators, truck drivers and registered nurses was headed to Alexandria, Louisiana, to set up an evacuation shelter.

After the storm, the team will feed, shelter and re-supply people in the areas affected by Gustav.

"Whatever small way you're able to help, it's a great feeling," said Kevin Wallace, a 23-year FDNY veteran who's helped after six disasters. "Whatever they need us to do, we do."

All 2,500 inmates in Orleans Parish would be bused out from state and local facilities, Orleans Parish Criminal Sheriff Marlin Gusman told the New Orleans Times-Picayune.

New Orleans Police Chief Warren Riley said this week that hundreds of officers will be posted in the uptown, downtown, Central City and West Bank areas to ensure an adequate law enforcement presence in the event of an emergency.

During Katrina, many New Orleans officers were accused of leaving their posts as widespread crime and looting permeated the city. Sixty-seven officers were fired for it, Riley said.

In addition to the police department's actions, at least 1,500 Louisiana National Guard members arrived in New Orleans on Friday.

Homeland Security Secretary Michael Chertoff said his concerns for New Orleans are twofold. First, he was worried about areas of potential weakness in the levee system, which he said the Army Corps of Engineers monitor closely, and second, rainfall.

"You can build levees that are 100 feet high; it's not going to keep the rain out of the city. A very, very intense period of rain could flood the city, because the pace of the rainfall could exceed the ability to pump out of the city," he said.

The only thing to do was prepare, he said.

"We evacuate; we protect the integrity of the levees; we continue to strengthen the levees; that's part of a total system of really driving down the risk to the people of New Orleans," he said.

The Louisiana National Guard has requested 20 helicopters from eight states to replace its helicopter air assault battalion, which is now serving in Iraq with its 20 UH-60 Black Hawks.

The Guard is asking for UH-60 helicopters for search and rescue, as well as CH-47s, Chinooks, which could drop large sandbags if the levees are breached.

A 40-person aviation headquarters unit also is being requested and probably will be provided by the Arkansas National Guard to handle air traffic control and communications for any air operations that might be needed.

In Texas, Gov. Rick Perry pre-emptively declared an emergency in 61 Texas counties. He said also the state had agreed to take into its shelters several thousand Louisiana residents, should they evacuate.