Tropical storm Barry is expected to come ashore along the Louisiana coast as a hurricane early Saturday, bringing a dangerous downpour that could inundate rivers, streets and homes.

As much as 25 inches (64 centimeters) of rain could fall in some areas, the U.S. National Hurricane Center said in an advisory at 1 p.m. in New York. The storm, expected to cause close to US$1 billion in damage, was bearing down on Louisiana’s central coast. On the current path, it may make landfall 125 miles west of New Orleans after 7 a.m. Saturday.

It’s top winds were at 65 miles per hour, up from 50 mph earlier, and it was 105 miles west southwest of the mouth of the Mississippi River. It will become a hurricane once winds reach 74 miles per hour, and Barry could potentially come ashore as a Category 1 storm, the weakest on the five-step Saffir-Simpson scale, according to the NHC.

“The big thing will be the rain with this system,” said Paul Walker, a meteorologist with AccuWeather Inc. in State College, Pennsylvania. “To put it in perspective, New Orleans gets about almost six inches in the month of July. They could get four times as much as they get for the entire month.”

Additionally, Barry has already curbed about half the production of energy resources in the Gulf of Mexico, helping lift oil prices. It’s also disrupted ship traffic on the Mississippi River, where water levels are rising.

After it comes ashore, it will quickly break up as it rains itself out. By next week, it will be bring about 1 inch of rain across southern Illinois and Indiana, which could benefit farmers there, said Ryan Truchelut, president of Weather Tiger LLC in Tallahassee, Florida. Barry probably won’t be remembered for its winds.

“The big story here is going to be the heavy rainfall,” said Truchelut. “From Lafayette to Biloxi and to the north inland there is going to be 10 to 20 inches of rainfall over the weekend and that is going to be a high-impact event.”

Companies have cut 59 per cent of oil and 49 per cent of natural gas output in the Gulf. Tropical-storm-force winds are reaching as far as 175 miles east of Barry’s center, according to the NHC’s advisory.

While New Orleans -- where an emergency was declared Wednesday -- won’t have a mandatory evacuation, residents should be prepared to shelter in place because the slow moving storm could bring heavy rain for 48 hours, Mayor LaToya Cantrell said at a press conference. The Mississippi is now forecast to crest at 19 feet, according to the National Weather Service. That should keep the river below the tops of levees in the city, according to Cantrell.

Louisiana is already under pressure from floods after the months of rain that have set records across the U.S. and prevented farm fields from being planted. The Mississippi River in the state has been at flood stage since January and, for the first time since the Bonnet Carre spillway was completed in 1937, the Army Corps of Engineers has had to open it twice in the same year to help prevent flooding in New Orleans and take pressure off levees.

Based on its current track, the storm will likely cause about $800 million to $900 million in damage, said Chuck Watson, a disaster modeler with Enki Research in Savannah, Georgia. That could balloon to US$3.2 billion if floods overwhelm New Orleans, he said.

A spokesman for the Army Corps of Engineers doesn’t believe levees will be topped by flood waters. The barriers on the lower Mississippi have been inspected daily since November when flooding became an issue.

U.S. benchmark West Texas Intermediate crude traded above $60 a barrel on Friday, while natural gas futures are headed for a third straight weekly gain.

Some other effects of the storm:

• Gulf of Mexico operators have shut-in 1.11 million barrels a day of oil production, the Bureau of Safety and Environmental Enforcement said in a notice. About 1.35 billion cubic feet a day of natural gas production is also halted.
• America’s grain elevators, cotton fields and cane crops in Barry’s path, and almost half of the U.S.’s exports of corn, soybeans and wheat get sent abroad from ports along the Mississippi River.
• The storm is putting 70 per cent of newly minted U.S. LNG capacity at risk, with Cheniere Energy Inc.’s Sabine Pass export terminal and Sempra Energy’s Cameron facility potentially in its path.
• Port Fourchon, a seaport on the Gulf of Mexico serving more than 90 per cent of the region’s deepwater oil production and acting as a land base for Louisiana Offshore Oil Port (LOOP), is under a mandatory evacuation order.
• The storm may have the biggest impact on oil products, with the Louisiana coast home to nearly 40 per cent of U.S. Gulf Coast refining capacity. Royal Dutch Shell Plc’s Norco and Convent refineries are said to be reducing rates on some units and sending nonessential workers home.
• The U.S. Coast Guard expects the New Orleans port to close Friday morning. At least 13 oil ships were waiting in the Gulf of Mexico Thursday, bound for ports that could be affected by the storm.
• Entergy Corp., which runs two nuclear power plants in Louisiana, said it’s keeping a close watch on the storm. Cleco Corp., which supplies power to about 288,000 retail customers in the state, said it’s monitoring Barry and has crews on standby to respond to outages.

In addition to Barry, the hurricane center is also tracking a second potential storm in the mid-Atlantic that has a 20 per cent chance of strengthening in the next five days. That system is still “a long, long, long way away,” Walker said.