"Unfortunately, all of Louisiana's coastline is currently in the forecast cone for Tropical Storm Ida, which is strengthening and could come ashore in Louisiana as a major hurricane as Gulf conditions are conducive for rapid intensification," Governor John Edwards said on Thursday.

"By Saturday evening, everyone should be in the location where they intend to ride out the storm.," he added.

The US National Hurricane Center said Ida was expected to cross the western stretch of Cuba as a tropical storm starting on Friday afternoon and then strengthen, reaching the Gulf Coast by Sunday.

"There is an increasing risk of life-threatening storm surge, damaging hurricane-force winds, and heavy rainfall Sunday and Monday, especially along the coast of Louisiana," the hurricane centre said.

"Ida certainly has the potential to be very bad," said Brian McNoldy, a hurricane researcher at the University of Miami.

Late on Thursday, Ida had sustained maximum winds of 65km/h and was travelling northwest at about 20km/h.

Tropical storm-force winds extended as far as 110km north of the centre.

The storm was forecast to deliver anywhere from 15-30cm of rain over parts of Jamaica, Cuba and the Cayman islands, with the potential for more in some isolated areas.

Forecasters warned of possible flash floods and mudslides and tidal storm surge of as much as one metre above normal, along with "large and destructive waves".

The Cayman Islands government said non-essential government offices were closed and four shelters were activated.

Australian Associated Press