By Alex Dobuzinskis
July 10 (Reuters) - Rainfall flooded streets of New Orleans on Wednesday, in the first effects from a weather system churning in the Gulf of Mexico that could grow into a hurricane capable of causing more severe flooding in the low-lying city, officials warned.
If a hurricane forms in the coming days and makes landfall close enough to New Orleans, city officials warned it could bring a storm surge that would raise the Mississippi River 20 feet (6 meters) above sea level and overtop some sections of the levee that protects the city.
The storm is most likely to make landfall west of New Orleans on Saturday, National Weather Service senior hurricane specialist Jack Beven said.
Louisiana Governor John Bel Edwards was preparing to declare a statewide emergency on Wednesday. "No one should take this storm lightly," he told a news conference.
The Mississippi River was already high from previous rains upriver, Edwards said.
New Orleans has been battered by devastating floods before, including 2005's Hurricane Katrina, which left most of the city underwater, killed hundreds of residents and displaced 130,000 people from Louisiana's largest city.
Foreshadowing the looming threat, New Orleans was hit early Wednesday by thunderstorms that meteorologists said were associated with the building storm. A water spout, a weather phenomenon that looks like a tornado, formed over Lake Pontchartrain near New Orleans and the Weather Service issued a tornado warning for the city.
City Hall was closed and many New Orleans streets were flooded after parts of the city received more than 8 inches of rain (20 cm).
The Gulf weather system is likely to develop at the least into a tropical storm, which would be named Tropical Storm Barry, Beven said.
"The forecast has it becoming a hurricane, but there's a possibility that it might not also," Beven said by phone from the National Hurricane Center in Miami.
Oil producers have curbed output and evacuated Gulf oil platforms as the storm approaches.
Southeast Louisiana is expected to be drenched by 4 to 6 inches (10 to 15 cm) of rain by the end of the week, with some areas receiving up to 18 inches (46 cm), Beven said.
New Orleans officials advised residents to gather water, non-perishable food and other emergency items ahead of the storm.
"If you haven't already prepared yourself and your family for a severe weather event, you need to go ahead and do that," Edwards said. (Reporting by Alex Dobuzinskis in Los Angeles additional reporting by Peter Sezekely in New York; editing by Scott Malone and Leslie Adler)
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