Tropical Storm Harvey, now spinning near Port O'Connor, Texas, is forecast to move back into the Gulf of Mexico today, the National Hurricane Center said.

It will meander over the Gulf for a couple of days before making a second landfall somewhere near the Texas/Louisiana border, likely on Wednesday.

Harvey is then expected to slowly move northeast across Louisiana and Arkansas as a tropical depression from Thursday into Saturday.

As it spins offshore, the storm is expected to dump an additional 15 to 25 inches of rain through Friday over the upper Texas coast and into southwestern Louisiana, exacerbating the life-threatening, catastrophic flooding in the Houston area, the hurricane center said. Isolated storm totals may reach 50 inches over the upper Texas coast, including the Houston/Galveston metropolitan area.

"Reliable weather forecasts still show taking whatever rain has already fallen around Houston and doubling it over the next 4-5 days," WeatherBell meteorologist Ryan Maue said.

Since Friday, an average of 26 inches of rain has fallen in Harris County, where Houston is located, the Weather Channel said. That much rain would provide drinking water for the entire county for roughly five years. Harris County is home to 4 million people, making it the third-largest county in the U.S.

The highest reported total from the storm so far is 30.56 inches in the Forest Oaks neighborhood of Houston.

Brief tornadoes may also form anywhere from Galveston eastward to just south of New Orleans, the National Weather Service warned.

As of 4 a.m. CDT, Harvey had maximum sustained winds of 40 mph with a few higher gusts reported. It was moving to the southeast at 3 mph.

Forecasters were also monitoring another system off the coast of Florida, which should become Tropical Storm Irma later today or on Tuesday. A Tropical Storm Watch has been posted for portions of the South and North Carolina coasts.