(CNN) - New Orleans is facing days of heavy rainfall after 9 inches of rain on Wednesday flooded parts of the city.
Storm surge and extensive flooding are forecast in the coming days thanks to Tropical Storm Barry, the first tropical system to hit the US this year.
The Mississippi River in New Orleans is forecast to crest Saturday at 19 feet, a level not seen since February 1950 and about 2.3 feet shy of the record set in April 1922, the National Weather Service said Thursday. The river initially was forecast to crest at 20 feet.
The city could get at least 10 inches of rain before this system moves out, CNN senior meteorologist Dave Hennen said.
The storm is moving slowly, the weather service said, so residents of the coast and in the lower Mississippi Valley could see heavy rainfall through the weekend and into early next week. Flash flooding and river flooding are likely.
Mandatory evacuations in at least 2 parishes
States of emergency have been declared in Orleans, Jefferson, St. Bernard, Plaquemines and St. Charles parishes. Jefferson Parish and Plaquemines Parish have instituted mandatory evacuations as a precaution in low-lying areas or those outside major levees.
Officials are expected to close dozens of floodgates to help mitigate the risk of flooding, according to Southeast Louisiana Flood Protection Authority East spokesman Antwan Harris, and FEMA has deployed personnel and supplies for staging in Louisiana and Texas, the agency said in a statement.
"Gulf Coast residents should prepare now for heavy rains, flooding and high wind impacts regardless of this storm's category," the FEMA statement said.
In New Orleans, 118 of city 120 pumps that drain neighborhoods are in working order, Sewerage & Water Board spokeswoman Courtney Barnes told CNN. The two that aren't are relatively small, she said, and are at stations with other functioning pumps in the Lakeview area and New Orleans East.
Still, the system of pumps, underground pipes and canals is only designed to remove 1 inch of rainwater in the first hour of a storm and a half inch in subsequent hours. It simply could not keep up with Wednesday's downpour, Barnes said, noting that any system in the country would have been outpaced.
"There's no system designed to pump that capacity of rain," she said.
'The real storm hasn't event hit'
Some residents aren't taking any chances.
Dannie Davis of New Orleans will evacuate, she told CNN on Thursday. She was struck by the flooding Wednesday, "and the real storm hasn't even hit," she said.
"I haven't seen this much rain and flooding before a hurricane in awhile," she said. "Who knows what's to come and whether the city will be able to handle it."
Another resident, Claire Grogan, was also planning to evacuate, she said.
For 40 years she's lived in the French Quarter, mere blocks from the Mississippi River, she said, and has never been scared. Now, that's changed.
"The river is so high that I am just scared to stay," Grogan said, adding that as a business owner, she also wants her employees to have the chance to leave if they want to.
CNN's Brandon Miller contributed to this report.