A tropical storm watch was issued Monday along the entire Louisiana (search) coast as a tropical depression gained strength in the Gulf of Mexico.

The watch was issued for about 280 miles along the Louisiana coast from the mouth of the Mississippi River (search) to Sabine Pass, Texas. A watch means tropical storm conditions are possible within 36 hours.

At 5 p.m EDT, the system was about 435 miles south of the mouth of the Mississippi River and moving north-northwest at 12 mph, according to the National Hurricane Center (search) in Miami.

The depression had top sustained winds of 35 mph, and could strengthen into a tropical storm Tuesday with top sustained winds of at least 39 mph, forecasters said.

Early Monday, the system made landfall over the Yucatan Peninsula and it could bring another 2 to 4 inches of rain over the peninsula's northern tip over the next day, forecasters said. The depression could bring a total of 10 inches of rain in some areas.

This is the third tropical depression of the Atlantic hurricane season, which began June 1 and ends Nov. 30. The next tropical storm would be named Cindy.