Republican officials abruptly announced late Saturday that they would delay their national convention until at least Tuesday afternoon because of Tropical Storm Isaac, which was expected to become a hurricane early Sunday and reach Florida later in the day.

As of late Saturday, Tampa was expected to avoid a direct hit but would almost certainly be pelted with high winds and rain that could cause major disruptions to the convention.

Tampa sits in a low-lying area prone to flooding, with many bridges and causeways. Convention delegates might need to be evacuated from their hotels, many of which are on beaches in nearby Clearwater and St. Petersburg. Locals who are staffing the convention could face problems getting to work. And the convention site is within a block of the water.

“Our first priority is ensuring the safety of delegates, alternates, guests, members of the media attending the Republican National Convention, and citizens of the Tampa Bay area,” Republican National Committee Chairman ­Reince Priebus said in a statement Saturday evening.

“We’ll know on Monday how severe this tropical storm is,” Priebus told reporters on a conference call Saturday night. “We’re not going to put delegates on a bunch of buses over bridges . . . and we can’t predict how severe the wind is going to be.”

Even if Tampa is unscathed by Tuesday, Republican officials will have to make a decision about whether to proceed if Isaac stays on its current track and hits farther north on the Gulf Coast. The 2008 Republican convention, which was in Minneapolis, was postponed a day because of Hurricane Gustav.

Republicans also will have to contend with the diverted attention of the media and the public, who may tune into hurricane coverage instead of the convention.

Russ Schriefer, a senior strategist for presidential candidate Mitt Romney’s campaign and who is overseeing the convention program, said officials were working to move Monday’s scheduled speakers onto programs for the following three days.

“We will absolutely be able to get our message out,” Schriefer told reporters Saturday night.

Monday’s theme was to be “We Can Do Better,” highlighting the country’s rising debt and lingering joblessness. Scheduled speakers included House Speaker John A. Boehner (Ohio), former Florida governor Jeb Bush, former Arkansas governor Mike Huckabee, South Carolina Gov. Nikki Haley and Sen. Rand Paul (Ky.).

Schriefer added that the roll-call vote that would make Romney’s nomination official, which was planned for Monday night, will now occur Tuesday.

Even before a final decision to delay the opening had been made, Romney advisers were rearranging the schedule for the week. Kyle Downey, spokesman for the convention, said the updated schedule should be released on Sunday afternoon.

The storm likely will come ashore in the U.S. sometime Tuesday, and the current track puts landfall in or near the Florida Panhandle. Convention officials plan to adapt as necessary the tone and tenor of the Tuesday sessions, depending on the severity.

“We remain hopeful the impact will be minimal,” Downey said. “But we will continue to monitor the situation and act accordingly.”

Vice President Biden also canceled a Tuesday campaign trip to Orlando and St. Augustine because of the storm; he had earlier canceled a planned Monday event in the Tampa area.

Heading into Tampa, Romney had been trying to build on the momentum following the largely successful rollout of Rep. Paul Ryan (Wis.) as his vice presidential running mate. But his task of winning over moderate voters became more challenging last week as a Missouri Senate candidate’s comments on “legitimate rape” and abortion — as well as Romney’s quip Friday about his birth certificate — highlighted the more extreme views within the Republican coalition.

Romney’s advisers have planned an elaborately choreographed convention aimed at presenting him as a successful businessman and compassionate family man.

“Help is on the way,” Romney said in a Saturday podcast previewing the convention, which will focus on his command of the economy and prescriptions to fix it.

“Certainly, for the next two months, the sole focus of the Romney campaign is going to be on jobs and the economy, debt and taxes and energy,” Virginia Gov. Robert F. McDonnell, a top Romney surrogate, said in an interview. “These are the things that Americans really care about, it’s what they’re talking about, it’s what the failed policies of this president have produced — a bad situation for our country — and it’s what the undecided voters are going to ultimately vote on.”

President Obama and his allies are intent on disrupting Romney’s narrative. Obama, in an interview with the Associated Press published Saturday, sought to discredit Romney by arguing that he has taken “extreme positions” and lacks serious ideas and peddles factual inaccuracies that will haunt him in the fall debates.

“I can’t speak to Governor Romney’s motivations,” Obama said in the interview. “What I can say is that he has signed up for positions, extreme positions, that are very consistent with positions that a number of House Republicans have taken. And whether he actually believes in those or not, I have no doubt that he would carry forward some of the things that he’s talked about.”

Obama singled out Romney’s plan for across-the-board tax cuts and said they would help the rich at the expense of everyone else, and he argued that his policies would be better for the middle class. Obama also alluded to Rep. Todd Akin’s statement last weekend that when a woman is the victim of “legitimate rape,” her body has a way to “shut that whole thing down,” so as not to become pregnant.

Romney quickly disavowed Akin’s comments last week and he has called on the Senate candidate to drop out of the Missouri race.

At a rally Saturday in Ohio, Romney tried to close the substantial gap with Obama among women with an appeal to their economic anxieties.

“Just a word to the women entrepreneurs out there,” Romney said. “If we become president and vice president, we want to speak to you, we want to help you. Women in this country are more likely to start businesses than men. Women need our help.”

This is a critical juncture for Romney in a race that has remained deadlocked after months of bitter negative advertising and personal attacks. Polling shows that Obama holds a slight advantage in some key battleground states, but Romney’s advisers are confident they will get a bounce from the Tampa convention.

“The convention is the ‘This is who I am’ moment for Mitt Romney,” former New Hampshire governor John Sununu said in an interview.

Felicia Sonmez in Powell, Ohio, contributed to this report.