(Reuters) - Presidential candidate Mitt Romney flew to Tampa on Tuesday to join fellow Republicans seeking to put their shortened convention back on track and prevent his message from being drowned out by a hurricane bearing down on the U.S. Gulf Coast.

Finally getting down to business after the storm threat upended the convention schedule, delegates will affirm Romney as the party's nominee in an evening capped by prime-time speeches by his wife, Ann, and New Jersey Governor Chris Christie.

Romney, who had originally planned to stay out of the spotlight until Thursday night when he accepts his party's nomination, decided to make an early appearance in the host city on Tuesday to be on hand for his wife's turn at the podium.

Republicans seeking to salvage the convention faced a stiff challenge: help Romney make an aggressive, memorable argument to voters to replace President Barack Obama while being careful to show sensitivity to those at risk from the hurricane.

Delegates gathering for the typically festive and partisan event were also under pressure to avoid the appearance of unseemly celebration while the Gulf Coast was under threat.

Isaac, upgraded to a Category 1 hurricane, was forecast to hit in the New Orleans area seven years after it was devastated by Hurricane Katrina - a painful reminder of how the mishandling of the disaster response under President George W. Bush stained the last Republican administration.

While Tampa was spared the brunt of Isaac's fury, a destructive landfall in Louisiana in the next day or so could create uncomfortable split-screen television images of the convention juxtaposed with the hurricane.

The Republican gathering will culminate with Romney's nationally televised acceptance speech on Thursday, the biggest speaking engagement of his political life as he heads into a 10-week sprint to the November 6 election.

He spent the past few days rehearsing at his New Hampshire vacation home before heading for Tampa, where his appearance could help energize delegates as the convention gets into full swing. He is scheduled to fly to Indianapolis to address the American Legion on Wednesday before returning to Tampa.

Running even with Obama or slightly behind him in most polls, Romney needs a bounce in popularity from the gathering, particularly in the 10 or so politically divided "swing states," including Florida itself, likely to decide the election.

Romney's campaign insisted the convention would give him momentum but sought to play down expectations of a significant "bump" in the polls that candidates traditionally enjoy after being nominated.

"I just think all bets are off about any kind of past performance being a predictor of the future," Stuart Stevens, Romney's senior adviser, told reporters, citing the uncertain impact of the storm threat and the fact that both parties' conventions are almost back-to-back.

Obama showed he was staying on top of the hurricane situation, warning Gulf Coast residents to make preparations, but he planned to go ahead with own campaign events in Iowa and Colorado later in the day.

Republicans have a lineup of speakers on Tuesday night who are expected to rip into Obama for his economic policies, widely seen as the president's most vulnerable point, and argue that the former private equity executive could do a better job.

Keeping the heat on Obama for his "you didn't build that" comment, convention planners have set the day's theme as "We Built It," in a bid to highlight what they see as the president's hostility toward small business.

SEEKING TO HUMANIZE ROMNEY

Ann Romney's address represents a prime opportunity to humanize her husband, who is often seen as having trouble connecting with ordinary Americans. Obama's campaign has sought to exploit this by emphasizing Romney's vast wealth.

In Tampa, part of Republican officials' aim is to present Romney's biography - as a private equity executive, Massachusetts governor and leader of the 2002 Salt Lake City Winter Olympics - in a flattering way that contrasts with the waves of attacks on Romney by the president and his allies.

Ann Romney, who suffers from multiple sclerosis and survived breast cancer, is perhaps his most effective surrogate.

"Having breast cancer wasn't easy," she told CBS's "This Morning" program in an interview that could help set a more sympathetic tone for the wealthy couple. "I've had several miscarriages actually, but having multiple sclerosis was a very, very hard time in my life."

Adding a personal touch with reporters on the plane to Tampa, she served them Welsh cookies baked from a family recipe. On landing, she went straight from the airport to the Tampa Bay Times Forum for a walk-through and a "mic check" at the lectern.

Expectations are highest, however, for the keynote speech by the fiery Christie, which is likely to be heavy on red-meat rhetoric for conservatives.

Many Romney supporters like Christie's in-your-face style, which contrasts with Romney's stiff demeanor and has made the New Jersey politician a rising political star. Christie was on Romney's vice presidential short list and is seen as a future presidential contender.

"You start turning it around tonight," Christie told ABC's "Good Morning America" program when asked how to overcome some voters' lack of enthusiasm for Romney.

The man Romney did pick as his running mate, Wisconsin congressman Paul Ryan, tops the bill on Wednesday.

Another speaker scheduled for Tuesday, Rick Santorum, is a different matter. The former Pennsylvania senator was the last obstacle standing in Romney's path to the nomination and had delivered attack after attack on Romney on the campaign trail.

Some Romney advisers disliked the idea of granting Santorum a speaking role but relented in the name of party unity.

ROLL CALL OF STATES

Tuesday's agenda will be dominated by the traditional roll call of state delegations, which will make Romney's nomination official, and endorsement of the party's election platform.

The platform was shaped heavily by conservatives, reflecting the party's move farther to the right, and some positions on social issues go beyond what many Republicans support.

The anti-abortion language, which makes no exceptions for rape or incest, was approved by the platform panel amid unflattering headlines caused by U.S. Representative Todd Akin, a Senate candidate in Missouri who has said women's bodies have a way to protect them from impregnation after "legitimate rape."

But uppermost in convention planners' minds was Isaac -- and the question of whether it would rob some of Romney's media attention. The storm forced convention organizers to compress the event into three days instead of four.

The Republicans' convention was also disrupted in 2008 when they chose to delay its start in St. Paul, Minnesota, as Hurricane Gustav hit Louisiana. Republicans then were still reeling from criticism of Bush's handling of Katrina, which killed more than 1,800 people and caused billions of dollars of damage along the coast.