Ports along the northern Gulf braced for the worst as Hurricane Ivan lashed the coasts of Alabama, Mississippi, Louisiana and the Florida Panhandle on Wednesday with 135 mph winds and pounding waves.

The National Hurricane Center is predicting the eye of Ivan will make landfall early Thursday -- around 4 a.m. ET -- across Mobile Bay in Alabama. Forecasters believe the hurricane may weaken slightly, but still will be a dangerous Category 3 storm when it hits land.

Currently, Ivan is a Category 4 (131-155 mph winds) on the Saffir-Simpson scale. Forecasters said swells in the center of the storm have measured 30 feet.

The National Weather Service said Ivan could bring a tidal surge of 10 to 16 feet, swamping a dozen blocks of downtown Mobile.

The Coast Guard Vessel Traffic Center New Orleans ceased operations at noon today effecting a safety zone from mile marker 88 to 106 at Southwest Pass, including the Intracoastal Waterway, restricting all vessel movements in that area.

At the same time, the Captain of the Port of New Orleans ordered all cargo operations shut down.

Ports from New Orleans to Pensacola, Fla. closed Tuesday afternoon after lashing down equipment and sending most vessels to sea. In Mobile, the Alabama State Port Authority secured cranes and other equipment, and all containers were lowered to two-high stacks.

Alabama ports spokeswoman Judith Adams said all vessels left the port Tuesday, and it could be next week before the port re-opens. "It's going to shove a lot of water down Mobile bay," said Steve Miller, a meteorologist with the National Weather Service in Mobile.

"If it follows the expected track, it won't be a near-miss like we've experienced over the past 10 years. This one will be the real deal," said Randy McKee, head of the National Weather Service office in Mobile.

Unless Ivan veers, it could surpass Hurricane Frederic, the Category 3 storm that hit in 1979, the benchmark by which most longtime area residents measure tropical systems. Frederic brought an eight-foot storm surge to the Port of Mobile.

The Coast Guard established a Crisis Action Center in New Orleans, which was manned by an Incident Management Team, after sending all non-essential personnel to seek higher ground.

In Florida, the Port of Panama City has a ship scheduled to arrive Thursday that was to be diverted. Port Director Chuck Porter said port officials' main concern was several million dollars worth of construction materials piled on the port dock for a renovation project. Porter said the lumber and other materials would be either lashed down or moved inside warehouses to prevent flying debris.

At the Port of New Orleans, seven working ships are tied up at port wharves for safe harbor.

By Janet Plume