Officials say they hope to begin laying out a revised schedule on Sunday.
As aides in Tampa scramble, Romney is taking a rare day off the campaign trail at his lakeside vacation home in New Hampshire, receiving updates on the storm and making final preparations for the Thursday speech with which he will accept his party's presidential nomination.
"The safety of those in Isaac's path is of the utmost importance," Romney tweeted after Republican officials announced they had called off Monday's convention proceedings.
Because of possible storm surges and flooding Isaac could bring, convention organizers said they were making contingency plans to move delegates who have been booked into beachfront hotels to other locations if necessary. They indicated the schedule shift also was meant to prevent overburdening emergency response personnel at the height of the storm.
The GOP made the announcement late Saturday, saying that while the convention would officially be gaveled into session on Monday as scheduled, events would be postponed until Tuesday.
With Isaac boring down on the coast, President Barack Obama, who was spending the weekend at the Camp David presidential retreat in Maryland, dispatched the Federal Emergency Management Agency to establish a command center and move more resources into the state. Vice President Joe Biden scrapped a planned campaign trip into Florida that was to counter the start of the GOP convention.
Republicans hope to use this week's convention to cast Romney as a determined leader with the know-how to fix the country's economy. They also want to introduce him as a family oriented figure to counter the image of him as a ruthless businessman as Democrats have sought to brand him.
Romney and his wife, Ann, looked to show off the more personal side with a joint interview airing Sunday.
"I wish everyone could see him how I see him, because as a mother, I've seen him, how compassionate he's been with me, as a wife and my raising these small children and how he always valued my work as being more important than his," Ann Romney said in the "Fox News Sunday" interview taped at the family's summer home in New Hampshire.
The candidate described his wife as his "best friend, obviously, and my counselor throughout my life," according to an advance transcript.
While the Romneys reveled in their convention, Obama was due to travel next week to college towns in Iowa, Colorado and Virginia to court young voters and college students. The president's nomination for a desired second term was to come a week later in Charlotte, N.C., during a Democratic convention beginning Sept. 4, right on the heels of the Republican convention.
In an interview with The Associated Press published Saturday, Obama sought to portray Romney as someone beholden to "extreme positions" on economic and social issues. Obama took pains to paint Romney and his running mate, Wisconsin Rep. Paul Ryan, as ideologues at a time when voters seem frustrated by government gridlock.
After a near-constant travel schedule since he was announced as the GOP vice presidential candidate, Ryan was also taking a rare break. Following a Saturday evening fundraiser in Manchester, N.H., he returned home to Janesville, Wis. Aides said Ryan planned a quiet Sunday. Then, before flying to Florida, he was to appear at a Monday rally in his hometown that was likely to offer him a hero's sendoff.
A few of Romney's former presidential rivals were holding events of their own in Tampa. Herman Cain and Minnesota Rep. Michele Bachmann - both have endorsed Romney - were appearing at a joint event. Texas Rep. Ron Paul, who hasn't conferred his blessing on the presumptive nominee, was anticipating thousands at a University of South Florida rally.
Associated Press writers Philip Elliott and Steve Peoples in New Hampshire and Ken Thomas in Washington contributed to this report.