(Adds cruise cancellations)
Sept 6 (Reuters) - As Hurricane Irma bore down on the southern United States on Wednesday, airlines adjusted flight schedules, made cancellations and assured passengers they would not have to pay unusually high fares ahead of the storm's arrival.
Irma, the second powerful hurricane to approach the United States in as many weeks, was expected to make landfall in Florida by the weekend, and as of Wednesday, it had already pummeled islands in the Caribbean with rain, pounding winds and surging surf.
While the storm's precise trajectory remained uncertain, airlines preemptively canceled flights in the likely affected regions and put in place travel waivers for customers to reschedule plans.
American Airlines, the largest U.S. carrier by passenger traffic, on Wednesday said it would begin winding down operations in south Florida, including Miami, Fort Lauderdale and West Palm Beach, on Friday. Miami-bound flights arriving on Friday from Europe and South America were canceled.
Delta Air Lines and JetBlue announced fare caps on flights out of Florida - $99 on JetBlue and $399 on Delta - for residents trying to get out of the storm's path.
"We want those trying to leave ahead of the hurricane to focus on their safe evacuation rather than worry about the cost of flights," JetBlue spokesman Doug McGraw said.
United Airlines, which took a substantial financial hit when Hurricane Harvey slammed into Texas last week, said it had suspended operations out of San Juan, Puerto Rico, a U.S. territory that was being raked by the very powerful Category 5 hurricane on Wednesday afternoon, and had extended a travel waiver to include cities in south Florida.
In some cases, before the storm struck, carriers added flights and upsized aircraft out of Florida and the Caribbean to accommodate as many passengers evacuating the area as possible. Fort Lauderdale-based Spirit Airlines said it expects its largest operational hub to be impacted and planned to move its operations center to Detroit on Thursday evening.
Beyond U.S. airlines, Canadian carriers Air Transat and WestJet Airlines on Wednesday both launched evacuation operations to remove passengers that could be affected by Hurricane Irma in the Dominican Republic, and Air Canada allowed passengers to change flights in impacted areas free-of-charge.
WestJet, Canada's second largest carrier, operated rescue flights to Punta Cana and Puerto Plata on Wednesday and could make additional trips to Santa Clara and Cayo Coco, Cuba on Thursday, airline spokeswoman Lauren Stewart said.
Carnival Cruise Lines, which has major operations in Florida, canceled two of its Bahamas-bound cruises and said it is likely that other schedules will be impacted as the storm's path and impact became more clear. (Reporting by Alana Wise in New York; Additional reporting by Allison Lampert in Montreal and David Shepardson in Washington; Editing by Sandra Maler)