MIAMI (AFP) - Tropical Storm Karen weakened early on Saturday as it churned off the US Gulf Coast, though forecasters warned it would still bring heavy rain across several southeastern US states.

The slow-moving storm was parked south of the state of Louisiana, and was not expected to make landfall until late on Saturday or early on Sunday, the National Hurricane Centre said.

At 0900 GMT Karen was located about 310 kilometres southwest of the mouth of the Mississippi river, packing sustained winds of 65 kilometres per hour and moving towards the northwest at 13 kilometres per hour.

Hurricane watches for the Gulf coastal region were cancelled overnight, but a Tropical Storm warning was in effect for a region that ran from the central coast of Louisiana east to the western gulf coast of Florida.

The area includes metropolitan New Orleans, still battered by the 2005 pounding it received from Hurricane Katrina.