Grain export facilities on the Louisiana Gulf were shuttered on Wednesday as Hurricane Isaac came ashore near the mouth of the Mississippi River, a major shipping outlet through which almost two-thirds of U.S. grain shipments flow every year.

But the facilities, which unload grain barges and load ocean-going vessels, could be back up and running by the end of the week, industry sources said.

The U.S. Coast Guard closed the river on Tuesday to all traffic from the Gulf of Mexico to Baton Rouge as the storm neared, while shippers secured boats and equipment and locked up grain storage bins in preparation for high winds and rain.

"If you can get vessels moving again through the channel and you don't have a huge backlog of traffic that needs to patiently move through, I would imagine that things will be back up and running very quickly," said a grain export trader who asked not to be named.

Unless an export facility sustains considerable damage that keeps it offline for an extended period, little, if any, business was expected to be shifted to other shipping points, such as the Pacific Northwest, the country's No. 2 port range.

About 55 to 65 percent of U.S. corn, soybeans and wheat exit the country via the Gulf Coast. Pacific Northwest facilities handle about 25 percent of the country's exports, while smaller volumes are shipped from the East Coast or from the Great Lakes via the St. Lawrence Seaway.

SLOW EXPORT PACE

U.S. corn and wheat exports have been sluggish in recent weeks due to high prices and global competition, while a large share of U.S. soybean exports have been loaded through the Pacific Northwest, a more direct trade route to major buyers in Asia.

"If we'd had some huge (grain export) program on the books you might have seen a lot of shuffling of the deck, but it's just so slow right now, so this is really just a small bump in the road," a grain trader said.

Slow-moving Hurricane Isaac was expected to linger over Louisiana through Thursday before moving further inland.

The Coast Guard will assess reopening the waterway once conditions are safer.

"The river is still closed from the mouth of the Mississippi to Baton Rouge. Coast Guard personnel and resources are on standby and as soon as conditions are favorable we will deploy resources and personnel to respond to people in distress," said U.S. Coast Guard Petty Officer Bill Colclough.

The Coast Guard received one report of a boat that had broken free of its moorings on the Mississippi, but has thus far not received any other official reports of barges or tow boats that have broken free.

"There could be more, but we haven't received any official reports. It's always a possibility in these types of conditions," Colclough said.

(Reporting by Karl Plume in Chicago; Editing by Dan Grebler)