Tropical Depression 13 poses a high threat level to the U.S. Gulf Coast region, including potential flooding risks in New Orleans which was devastated by high waters from Hurricane Katrina in 2005. Louisiana Gov. Bobby Jindal has issued a state of emergency in advance of the storm, likely to intensify to tropical storm status with drenching rainfall.

This is a developing story on Friday with potential for significant impact into the Labor Day weekend and early next week that residents along the coasts of Alabama, Mississippi, Louisiana and even Texas should closely monitor through the weekend.

Forecasters say the storm has the potential to drench the low-lying region with up to 20 inches of rainfall before it ends. In Louisiana, Gov. Jindal said he is concerned about the serious threat of flash flooding from the storm in his state and he declared a state of emergency late Thursday as the system continued to develop.

The tropical depression is likely to become Tropical Storm Lee, the 12th named storm of the Atlantic hurricane season. Last week, Irene became the first hurricane to strike the U.S. since Ike in 2008.

Tropical storm warnings have been posted from Mississippi to Texas, including New Orleans, where current forecast models show the biggest threat and potential impact. The National Hurricane Center said the system will pour massive amounts of rain over southern areas of the coast.

Already Friday, New Orleans is facing locally heavy rainfall possible from the storm. The forecast calls for a 70 percent chance of precipitation Friday and Saturday, with easterly winds gusting from 20 to 35 miles per hour.

Tropical Depression 13, likely to become Tropical Storm Lee, has a slow northwest movement forecast through Friday, followed by a turn toward the north on Friday night and Saturday. The center of the cyclone is expected to approach south Louisiana during the weekend. Gradual strengthening is forecast, and the depression could become a tropical storm on Friday.

Forecasters say isolated amounts of rainfall of 20 inches are possible, with widespread accumulations of 10 to 15 inches. Also, storm surge water levels could rise by as much as two to four feet above ground level of onshore flow.

New Orleans was severely damaged by inland flooding from Hurricane Katrina after water from torrential rainfall breached levees. Inland flooding is often the most damaging aspect of tropical storms and hurricanes that strike the U.S., not wind.