"The threat for damaging winds and deadly storm surge is increasing."

There's a 90% chance a tropical depression will form within the next 48 hours.

Torrential rain could result in life-threatening flooding.

The second storm of the 2019 Atlantic hurricane season was expected to form later Wednesday or Thursday along the Gulf Coast and is forecast to make landfall around Louisiana on Saturday as a treacherous storm or hurricane.

A hurricane watch was issued late Wednesday for most of the Louisiana coast, meaning that at least tropical-storm-force winds are forecast within the next 48 hours.

The weather disturbance, currently spinning off the coast of the Florida Panhandle, could either form as a tropical depression or a tropical storm. If the depression's winds reach 39 mph, it would become Tropical Storm Barry.

It's then expected to hit the Gulf Coast as a hurricane on Saturday, the National Hurricane Center said.

"This system has the potential to become a dangerous hurricane," the National Weather Service in Lake Charles, Louisiana, said on its Facebook page. "The threat for damaging winds and deadly storm surge is increasing."

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A storm surge watch was in effect for portions of Louisiana as the system gathered strength Wednesday.

The storm could bring more heavy rain and flooding to New Orleans, which was inundated with up to half a foot of rain on Wednesday morning, triggering a flash flood emergency for the area. A tornado or waterspout was also spotted near the University of New Orleans, WWL-TV said.

Even more concerning, the Mississippi River in New Orleans is now forecast to crest near 20 feet on Saturday, the weather service said – and the average levee height for New Orleans is 20 feet, said meteorologist David Bernard of Fox 8 in New Orleans.

University of Georgia meteorologist Marshall Shepherd called this "a potentially dire situation."

Louisiana Gov. John Bel Edwards declared a state of emergency Wednesday for all of Louisiana because of the possibility of flooding, winds and storm surge throughout the state.

“There could be a considerable amount of overtopping of Mississippi River levees in Plaquemines Parish on both the east bank and the west bank,” Edwards said at a Wednesday news conference.

A mandatory evacuation notice has been issued to members of the Plaquemines Parish community, starting Thursday at 6 a.m., according to the Monroe News Star. Evacuees will be housed in nearby West Monroe.

As of 5 p.m. ET, the system had winds of 30 mph and was located about 125 miles from the mouth of the Mississippi River. It was moving to the west-southwest at 8 mph.

Edwards ordered the Louisiana National Guard to begin deploying soldiers and high-water vehicles to the state's most vulnerable areas.

New Orleans Mayor LaToya Cantrell declared a state of emergency Wednesday afternoon. She said in a tweet that predicted conditions would warrant the use of "all extraordinary measures appropriate to ensure the public health, safety, welfare, and convenience."

The National Hurricane Center said Wednesday that there's a 100% chance a tropical depression will form within the next 48 hours in the Gulf of Mexico.

Rain, and lots of it appears likely to be the main threat from the storm.

"Regardless of the eventual track and intensity of the system, heavy rainfall is expected from the Florida Panhandle to the Upper Texas Coast extending inland across portions of the Lower Mississippi Valley, much of Louisiana and eastern Texas," the hurricane center said in its 8 a.m. advisory.

Up to 18 inches of rain is possible, the hurricane center said, while BAM Weather meteorologist Ryan Maue said that "totals probably will exceed 20-30 inches in Louisiana."

AccuWeather meteorologist Dan Kottlowski said that "right now, our greatest concern is for torrential rain that would result in life-threatening flooding."

Officials in New Orleans are monitoring for any potential storm surge impacts on the Mississippi River, AccuWeather said.

Tropical systems are occasional visitors to the U.S. in July: The most recent July hurricane to hit the continental U.S. was Hurricane Arthur in North Carolina in 2014, according to Colorado State University meteorologist Phil Klotzbach.

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"The most recent July tropical storm landfall was Tropical Storm Emily in Florida in 2017," he said.

The strongest recent storm to make landfall in the United States in July was Hurricane Dennis, which hit the western Florida Panhandle on July 10, 2005, as a Category 3 hurricane, the Weather Channel said.

Contributing: The Associated Press; The Daily Advertiser