Flash flooding from heavy rains battered New Orleans on Wednesday, and the worst might be yet to come. Meteorologists are predicting that the Mississippi River could rise up to about 19 to 20 feet by the weekend, which is the height of the city's levees. The entire Gulf Coast meanwhile braced for major thunderstorms, tropical storms and possibly a hurricane over the next couple of days. In New Orleans, more than 6 inches of rain fell on the Big Easy between 7:41 a.m. and 10:45 a.m. Wednesday, as residents and visitors to the popular tourist city, fled for cover or higher ground. The National Weather Service issued a flash flood warning at 7:41 a.m. and upgraded that to a flash flood emergency at 9:02 a.m., acknowledging that "flash flooding is already occurring with numerous streets and underpasses severely flooded." "Even though I grew up with Midwestern tornadoes and summer storms, this was next level in terms of the absolute deluge of water coming down so fast," California high school teacher Ellen Austin, in town for a convention, told NBC affiliate WDSU. "The water just came up in the streets in what felt like no time at all. And we have been cut off, with doors blocked with towels to keep water out, since this morning. It's been a bit surreal." A waterspout, a kind of a tornado that forms over a body of water, was spotted over Lake Pontchartain, WDSU reported. Louisiana Gov. John Bel Edwards said heavy rains threaten to be too much for levees protecting Plaquemines Parish which extends southeast, into the Gulf of Mexico. "Right now, we believe that any overtopping of the levees will be a relatively short duration of about 12 hours, but that is still a very, very significant hazard," Edwards said Wednesday morning. "We're not sure whether the state will be opening any shelters yet." According to the National Weather Service, the surge could raise the river to 19 feet, only one foot below the height of the New Orleans levee, and the highest the river has been in New Orleans in 70 years. The prediction was subject to change, becoming more precise as the storm got closer to shore. Meteorologists warned of a chance that the storm could linger in the Gulf, strengthening over warm waters and landing sometime this weekend. The Gulf of Mexico is warmer than usual right now, with temperatures typical for August, which was feeding the cluster of storms. Officials also said Wednesday would be one of the hottest days of the summer for Gulf Coast states, with temperatures expected to go above 105 degrees by the afternoon.