(CNN) -- The National Hurricane Center issued a tropical storm warning for the northern coast of the Gulf of Mexico as the fifth tropical depression of the Atlantic hurricane season formed in the southeastern Gulf.
The storm -- which would be named Danielle if, as expected, it reaches tropical storm status -- grew from tropical wave status about 375 miles southeast of the mouth of the Mississippi River and was headed in that direction at about 6 mph. Tropical Depression 5's top sustained winds reached 35 mph -- just short of the 39 mph tropical storm threshold.
The tropical storm warning covers the coast from Destin, Florida, to Intracoastal City, Louisiana, including Lake Pontchartrain and New Orleans. A warning means that tropical storm conditions are expected in the area within 36 hours.
Forecasters, however, said they did not expect more than "modest strengthening" as the storm makes a more northerly turn before coming ashore.
Preparing for the worst, Louisiana's St. Bernard Parish activated its severe weather plan for oil spill operators. Earlier Tuesday, retired Coast Guard Adm. Thad Allen said that attempts to complete the relief well expected to permanently stop BP's oil spill will be delayed because of the approaching weather system.