President Barack Obama has declared a state of emergency in Louisiana, as Tropical Storm Isaac threatens to hit the US as a category two hurricane, the BBC informs. Isaac is heading for New Orleans, possibly as early as Tuesday night, nearly seven years to the day after Hurricane Katrina devastated the city. The Republican Party delayed by a day the start of its national convention in Tampa, Florida.Isaac killed at least 24 people in Haiti and the Dominican Republic. The storm wrought significant flooding and damage in the Caribbean. The US National Hurricane Center (NHC) warns Isaac could reach category two strength, with top winds of 100mph (160km/h). The forecast was revised up from category one.President Obama approved Louisiana’s request for a federal disaster declaration, making available federal funds for recovery activities such as clearing debris. The governors of Louisiana, Florida, Mississippi and Alabama have declared emergencies in their states. The Republican governors of Alabama, Louisiana and Mississippi have cancelled their trips to their party’s convention to focus on disaster prevention efforts. Isaac is already a large storm and could bring significant damage to areas within hundreds of miles of its centre, officials warn. The NHC said that at 02:00 EDT on Tuesday (06:00 GMT), Isaac was centred about 145 miles (235km) south-east of the mouth of the Mississippi river, with maximum sustained wind speeds of 70mph (110km/h). The storm is moving forward at about 12mph and storm winds extend out about 205 miles (335km) from the centre. The NHC warned that wind speeds could reach between 96-110mph before the storm makes landfall. Evacuations have already been ordered for some low-lying Louisiana parishes and parts of coastal Alabama. Wednesday is the seventh anniversary of Hurricane Katrina, which strengthened in the Gulf to a category five storm, before weakening to category three by the time it reached New Orleans. Federal officials said the levees around New Orleans are now equipped to handle storms stronger than Isaac. Levee failures led to the catastrophic flooding in the area after Katrina.“It’s a much more robust system than what it was when Katrina came ashore,” Federal Emergency Management Agency Administrator Craig Fugate said in a conference call with reporters. Mr Fugate also said that Isaac was not just a New Orleans storm. “This is a Gulf Coast storm. Some of the heaviest impact may be in Alabama and Mississippi,” he said.