"I would like, obviously, to keep in our thoughts and prayers the people on the Gulf Coast, especially in New Orleans, that are threatened by this terrible natural disaster of a hurricane," McCain said, recalling the devastation New Orleans suffered after Hurricane Katrina flooded the city three years ago.
The Arizona senator appeared onstage with Palin at a baseball park rally under a hot sun outside Pittsburgh. To shouts of "Sa-rah! Sa-rah!" the Alaska governor thanked the crowd for the warm welcome.
"And it is warm! Not something I'm really used to," Palin said, laughing.
McCain aides say the campaign has brought in $7 million online since Palin's selection was announced Friday and that her strong anti-abortion credentials have helped energize conservatives, especially conservative women.
But the Palin rollout threatened to be overshadowed by Gustav, with the storm likely to change the course of the Republican convention scheduled to open Monday in St. Paul.
Gulf state governors could decide to remain at home if the storm threatens to bring serious damage. It could also affect Monday's opening-night address by President Bush. Gustav's projected path suggests it will make landfall late Monday or early Tuesday on Louisiana's central coast.
Earlier, in a television interview, McCain suggested convention plans may well be altered if Gustav continues on its projected path.
"You know it just wouldn't be appropriate to have a festive occasion while a near tragedy or a terrible challenge is presented in the form of a natural disaster, so we're monitoring it from day to day and I'm saying a few prayers, too."
He commented in an interview taped for "Fox News Sunday."
A top McCain aide, Mark Salter, said the campaign is drawing up contingency plans for what to do about the convention depending on when and where the storm hits. But he cautioned that it didn't mean the gathering would be canceled outright.
"It might change what we do at the convention" but wouldn't necessarily mean calling it off, Salter said.
Democratic presidential nominee Barack Obama, in his first direct comment on McCain's unexpected running-mate choice, said he had called her on Friday to wish her luck "but not too much."
McCain and Palin made a morning stop at Tom's Diner in Pittsburgh's trendy Southside neighborhood. The running mates, with spouses in tow, greeted patrons and posed for pictures. Palin's daughters Willow and Piper were also on hand, with Willow carrying Palin's 4-month old son, Trig.
The first-term Alaska governor told reporters she was having fun in her new role. "It's great to see another part of the country," she said. She also said she'd managed to get a little sleep during the night.
"We're used to not getting too much sleep," she said, nodding her head toward the sleeping infant.
Palin also issued her first fundraising appeal, saying in an e-mail, "Some of life's greatest opportunities come unexpectedly, and this is certainly the case for me."
A day after his surprise selection of Palin, McCain planned to work part of the day on his convention acceptance speech.
The Democratic team of Obama and Joe Biden also began their day with a diner stop - in the Youngstown, Ohio, suburb of Boardman - as they pressed on with their post-Democratic convention bus tour of Rust Belt battleground states.
Obama said in a television interview that he had wished Palin luck "but not too much luck on the campaign trail" in a brief congratulatory phone call on Friday. He told CBS' "60 Minutes" he had yet to meet Palin but "she seems to have a compelling life story. Obviously, she's a fine mother and an up-and-coming public servant."
Of his own choice for a ticket-mate, Obama said Biden "can step in and become president. And I don't think anybody has any doubt about that."
He also said he wanted the "counsel and advice of somebody who's not going to agree with me 100 percent of the time." The Delaware senator, who chairs the Senate Foreign Relations Committee, has a reputation for outspokenness. "Joe Biden doesn't bite his tongue," Obama said in the interview that was taped Friday night in Pittsburgh.
As Republicans began to gather in St. Paul, a new Obama ad that began airing nationally on cable television on Saturday acknowledged McCain's selection of Palin - but in images and words that left no doubt that Obama still wants the public to judge McCain by the policies of Bush.
"Well, he's made his choice," the ad states, "But for the rest of us, there's still no change."
During their diner stop, Obama and Biden and their wives chatted with patrons and told reporters they hoped the lessons learned from Hurricane Katrina would help the Gulf Coast this time.
"Hopefully we've learned from that tragedy," Obama said. Biden said the region was much better prepared than before Katrina.
"Just pray to God that those levees hold," he said.
With memories still vivid of the devastation wrought by Hurricanes Katrina and Rita in 2005, the possibility of serious damage threatened to cast a pall over the convention. It also could keep away some prominent governors - including Louisiana's Bobby Jindal and Mississippi's Haley Barbour. Depending on the path the storm takes, it could also affect the plans of governors Bob Riley of Alabama, Rick Perry of Texas and Charlie Crist of Florida.
Bush, faced with the chance of another devastating hurricane during his presidency, called Gulf Coast governors on Saturday and conferred with federal officials to keep a close watch on developments, said spokesman Scott Stanzel.
Forecasters on Saturday said Gustav had strengthened to a Category 4 storm with maximum sustained winds near 145 mph. The National Hurricane Center called it an "extremely dangerous" storm.
The president has been widely criticized for the way the government dealt with Katrina and its aftermath.
But the convention was still on schedule in St. Paul.
"There are no plans for any postponement," said Mike Miller, director of operations. "We plan to start when we're going to start and end when we're going to end.
Convention workers put up new barricades and closed off streets as Republicans made final preparations for the four-day GOP gathering at the Xcel Energy Center. Workers inside the arena were putting finishing touches on the stage and checking red telephones installed in the each delegation's seating area. The delegates' chairs were roped off with yellow caution tape in an effort to keep people from sitting on them.
Set-up crews and guards took a few seconds to take pictures of themselves in front of the large screen on the podium, which displayed an image of an American flag waving in the wind. Big signs ringing the inside of the arena highlight one of McCain's campaign themes, "Country First."
(Copyright 2008 by The Associated Press. All Rights Reserved.)