The southern coast of the U.S. is bracing for the arrival of Hurricane Ida, which is moving across the Gulf of Mexico and could make landfall as early as Tuesday.

A hurricane watch is underway across more than 322 kilometres of coastline, from the Florida Panhandle to Louisiana, where Gov. Bobby Jindal declared a state of emergency on Sunday.

The hurricane watch means a storm with sustained winds of at least 119 kilometres per hour could strike the area by Tuesday. It also mobilizes public resources used in emergencies.

New Orleans doesn't lie in the hurricane-watch area. But some segments of southeast Louisiana that are not protected by levees could be at risk of flooding, if the storm creates high winds and high tides there.

In Mexico, a hurricane warning was discontinued as of 7 p.m. Sunday evening.

On Sunday, rains and high winds battered Cancun, leading nightclub owners and restaurateurs to board up windows. But no serious damage was reported.

The U.S. National Hurricane Center said Ida's winds are approaching 170 km/h.

Ida is moving northwest at close to 19 km/h. The centre of the hurricane was 720 km south-southeast of the mouth of the Mississippi River late on Sunday afternoon.

Ida could also pick up steam as it continues to move across the Gulf of Mexico's warm, open waters.

However, Dennis Feltgen, of the National Hurricane Center, told CTV News Channel that Ida will be "gradually be absorbed by a cold front" as it makes landfall on Tuesday, and should lose some of its energy.

On Sunday, officials in El Salvador blamed dozens of deaths on residual rains from Ida as it moved through neighbouring Nicaragua.

Interior Minister Humberto Centeno said Sunday that 91 people had died in flooding that followed three days of heavy rain. Another 60 people are still missing, and 7,000 are in shelters.

According to Centeno, the deaths occurred in five of the country's 14 provinces.

The storm hammered Nicaragua's Atlantic coast on Thursday, destroying 500 homes, as well as roads and bridges.

However, U.S. officials at the National Hurricane Center in Miami said the rains in El Salvador were caused by a separate, low-pressure system that settled off the country's Pacific coast. While Ida may have helped steer that system, they said the deaths cannot be attributed to the storm.

"Because Ida is in the northwest Caribbean, there is a very large weakness in the steering currents in the middle levels of the atmosphere that's making this thing move on shore near El Salvador from the eastern Pacific," U.S. Navy hurricane specialist Dave Roberts told The Associated Press.

"If there were deaths associated with this rainfall amount in El Salvador, I would not link it to Ida."

With files from The Associated Press