At 400 miles wide, Ida -- once a Category 2 hurricane -- is the first tropical storm to make landfall in the Gulf region this late in the season since Tropical Storm Keith in 1988.
Pam Hurst, a Gulf Shores, Ala., resident, said she has noticed a difference with this disturbance.
"It's cold ... usually hurricanes aren't so cold. It's usually a little more muggy," she said.
Ocean levels along the Gulf coast have been rising to 3 to 6 feet above sea level, resulting in 6- to 10-foot waves.
It's tempting for surfers, but public safety officials warned people to stay out of the water.
"This is not the place to learn," Bob West, Pensacola Beach public safety director, told "Good Morning America." "It's extremely dangerous out there."
All around the region, the storm is having an effect.
Business owners from Pascagoula, Miss., to Panama City, Fla., prepared for Ida's arrival by stocking up on sandbags and boarding up windows. Road crews in Destin, Fla., cleared storm drains in an attempt to lessen the expected flooding.
Nearly 30 percent of oil and natural gas production in the Gulf of Mexico has been shut down.
With Ida weakening, most offshore oil rigs in the Gulf will not see any damage, said Jim Rouiller, senior energy meteorologist at private forecaster Planalytics Inc. Rouiller said that by Tuesday there would be normal operations across the production region.
Oil prices eased to $79 a barrel after Ida was downgraded from a Category 2 hurricane.
The Coast Guard closed the Port of Mobile, halting traffic on Mobile Bay, and authorities closed schools and government offices in coastal counties in Alabama and Florida, telling residents of flood-prone areas and mobile homes to evacuate.
The U.S. Coast Guard airlifted two women off of an oil rig in the Gulf -- about 80 miles south of New Orleans -- because of damage caused by the storm.
As Ida weakens, it's throwing rain from New Orleans to Mobile, Ala., and Pensacola. Flooding is a key concern, and Pensacola's annual rainfall had already been a foot above normal before the storm.
Flood watches are in effect for six southern states through Wednesday, and forecasters predict Ida will bring heavy rain as far north as Atlanta, where record-breaking floods killed seven people in September.
El Niño Played Role in Season's Storms
Experts say that El Niño likely played a part in keeping the Atlantic hurricane season mild.
"El Niño generally produces stronger wind shear in the Atlantic. That's when the winds are different in the upper and lower levels of the atmosphere, tends to tear hurricanes apart and we saw that with a number of systems this year," said James Franklin, hurricane specialist unit chief with the National Hurricane Center.
Ida's current has already pulled days of heavy rains into El Salvador, where at least 124 people have died.
Hurricane Ida swept through the Nicaragua's Atlantic Coast last Thursday, leaving nearly 500 homes, as well as roads, bridges and public buildings destroyed.
ABC News' Monica Nista and The Associated Press contributed to this report.