Tropical Storm Matthew, the 13th named storm of the 2004 hurricane season, flooded roads and homes across southeastern Louisiana on Saturday as it blew toward the Gulf of Mexico with high tides and torrential rainfall.

The town of Houma received 7.2 inches of rain in 24 hours, said Frank Revitte, a forecaster with the National Weather Service (search) in Slidell.

Tides were up to 4 feet above normal, causing flooding in the coastal towns of Montegut, Dulac and Cocodrie, said Michael Deroche, emergency preparedness director in Terrebonne Parish (search). A state of emergency was declared in the parish and two emergency shelters were opened.

"We have one humongous mess," Deroche said.

Officials on Grand Isle, Louisiana's only inhabited barrier island, decided against ordering evacuations, said police Capt. Bruce Francois. Although side roads were flooded, the only road connecting the island to the mainland remained open.

"The pumps are pumping, everything's working, so we should be OK if we don't get too much more rain," Francois said.

Farther inland, 4.17 inches of rain fell overnight at New Orleans and 5.29 inches fell at Baton Rouge.

The storm later weakened and was downgraded to a tropical depression.

At 11 a.m., the poorly defined center of the system was about 270 miles southwest of the mouth of the Mississippi River (search), and its top sustained wind speed had decreased to 35 mph. It was moving toward the north-northeast at around 10 mph.