BWI becoming a "focal city" for Southwest's likely shift abroad will help ensure that growth, he said. He said any other international growth for BWI would depend on market demand, but nothing is determined.

Laraba said Southwest is assessing the viability of adding many destinations to its portfolio, but would not name any.

At first, such destinations would likely be international airports that are close to the United States, given the current abilities of Southwest's fleet. In addition to Baltimore, international Southwest flights will begin Tuesday in Atlanta and Orlando, though Baltimore has the most.

The three flights Southwest takes over in Baltimore — to Aruba, Nassau in the Bahamas and Montego Bay in Jamaica — are all flights that AirTran already operated out of the airport. But once Southwest has a firm footing on those routes, Baltimore will continue to be a jumping-off point for new locales, Laraba said.

"It just opens a huge door," she said. "We really have no idea where it can take us, but we're excited about what we can see in the near future."

Some customers of Southwest are excited, too, though others not so much.

Chris and Cecilia Russo, 73 and 67, respectively, of Rumsey Island in Harford County, said they have mixed feelings about Southwest's venture into international waters.

The couple, awaiting a flight at BWI on a recent afternoon, said they took an AirTran flight to Aruba from BWI last year, so that's nothing new. They also used to take AirTran to Sarasota, Fla. — they have a condo down in Fort Myers — and it was convenient until Southwest discontinued the flight.

"That really put a number on us," Chris Russo said.

Convenience on airlines all depends on where you want to go, the couple said, so they'll wait to see what flights Southwest decides to add, instead of end.

Stacie Siekierski, 64, of Frederick is a Southwest fan, if an infrequent international flier, she said. Still, new international flights out of BWI would be a draw.

Every time Siekierski flies she has a choice to make, she said, because she lives about "equidistant" from BWI, Dulles and Ronald Reagon Washington National Airport.

Still, if a flight is available, BWI is her "first pick every time," she said.

Siekierski's friend, Mike Isaacs, also 64 and from Frederick, said he will be most interested to see whether Southwest eventually extends its reach beyond the Caribbean.

"If Southwest starts competing with the bigger places and carriers," he said, "that would be great."