Tonight, tropical storm isaac is gathering strength every hour as it barrels toward florida. It's expected to become a hurricane by monday. And already the waves are 10-feet high. So nearly 1 million... See More
Tonight, tropical storm isaac is gathering strength every hour as it barrels toward florida. It's expected to become a hurricane by monday. And already the waves are 10-feet high. So nearly 1 million people in tampa, home to the republi national convention, will have to decide what to do. Take a look at the current projected path. Haiti. The dominican republic will be hit friday. Then cuba on saturday and sunday. Then on monday, it moves into the florida keys. And by tuesday, moving off the coast of tampa and the great convention. And a local headline there says it all, "who invited isaac." Abc's matt gutman is on the ground in florida tonight. Matt. Reporter: Hey, diane. 50,000 delegates invited. Isaac could be a very unwelcome guest here in tampa, where the convention center, most of the hotels for the delicates, are right in the flood zone. Tonight, isaac is charging through the caribbean. 600 miles across with winds whipping up to 50 miles per hour. Isaac flooding parts of puerto rico and neighboring islands. Heavy rain bands spinning out 300 miles out from the center. 200 people alone evacuated from guantanamo bay, cuba, where u.S. Troops tonight are sandbagging buildings and, in miami, they're feverishly buying provisions. Every family should be prepared to sustain themselves for up to 72 hours. Reporter: In tampa, all eyes and headlines on the storm. But it happens that tampa is one of the most flood-prone cities in the country. If you have the right storm at the right angle, obviously, it has the ability to funnel a lot of that water right up into the bay. As many as 800,000 people live in the evacuation zone and would have to leave if a category 1 threatened tampa. Right anytime in the middle of that evacuation zone, the convention center. A tropical storm could bring the feet up eight feet. We'd be sub merged. Travel delays are expected. Airlines already allowing passengers to change tickets without penalty. They're not the only ones changing itineraries. Abc has learned that security officials from other parts of the state have cancelled their plans to help at the convention. To help their own communities get ready. And, diane, tampa is so low lying that even a moderate storm of 40 to 45 miles per hour could submerge the roads and bridges you see behind me. That gives you a sense of how vulnerable this city really is. Diane. That's just a tropical storm. It's 74 miles per hour to be a cat 1. Thanks so much, matt.
This transcript has been automatically generated and may not be 100% accurate.