Washington: As Hurricane Isaac hit southeast Louisiana on the eve of the seventh anniversary of catastrophic Hurricane Katrina, the state's Indian-American Governor Bobby Jindal warned residents to prepare for the hard times ahead.

Packing 80-mph winds and torrential, stinging rains, the storm made landfall at Plaquemines Parish at 6.45 p.m. As it began battering New Orleans, Louisiana's largest city and a major U.S port that was devastated by Katrina.

Isaac's eye then "wobbled westward" and moved back over land by 9 p.m., all the while keeping up its strength as it lashed southeast Louisiana, CNN reported citing the National Hurricane Centre.

"This is a serious storm. It's a slow-moving storm. It's important that our folks take it seriously," said Jindal, a rising Republican star, who skipped the party's national convention in Tampa Florida to deal with the situation at home.

As tropical storm Isaac, now upgraded to category one hurricane, approached the Gulf Coast, Jindal also shot off a letter to President Barack Obama asking for more federal help, urging him to reimburse Louisiana for the full cost of its preparations.

"Given the extraordinary developments of this storm and its approaching impact on the state of Louisiana, I ask that you exercise your discretion to approve the state's pending request for all emergency protective measures," he wrote.

Obama's original disaster declaration, issued Monday, doesn't cover the expenses Louisiana is racking up as it prepares for Isaac, according to Jindal's letter.

Louisiana has already spent $8 million, Jindal wrote. The declaration provides for direct federal assistance, for which the state will bear 25 percent of the cost.

In response Obama, who has declared states of emergency in parts of Louisiana and Mississippi, said at a campaign event in Ames, Iowa: "America will be there to help folks recover no matter what this storm brings."

"Because when disaster strikes, we're not Democrats or Republicans first, we are Americans first."

Asked about Jindal's letter, White House press secretary Jay Carney said the president wanted to make sure Louisiana had immediate support "and there will be time to explore if additional declarations are necessary" to support potentially impacted states.

Meanwhile, Republican presidential candidate Mitt Romney also spoke with Jindal telling him his campaign was "ready to help as much as we can", CNN said citing a campaign official.