7:40 p.m.: The low pressure system in the Gulf of Mexico south of Louisiana has been upgraded to Tropical Depression No. 13, according to the National Weather Service.

In addition, Gov. Bobby Jindal issued a state of emergency for Louisiana Thursday evening, anticipating heavy rains forecast from the system which could become a tropical storm by the weekend.

A Tropical Storm Warning has been issued for the coast of the northern Gulf of Mexico from Pascagoula Mississippi westward to Sabine Pass Texas.

The center of TD13 was located near latitude 26.6 north, longitude 91.4 west. The depression is moving toward the northwest near 6 mph.

A slow northwestward motion is forecast through Friday followed by a turn toward the north Friday night or Saturday. On this track the center of the cyclone is expected to approach the coast of southern Louisiana on Saturday, according to the National Weather Service.

Maximum sustained winds are near 35 mph with higher gusts. Some strengthening is forecast during the next 48 hours and the depression could become a tropical storm on Friday.

Bands of rain associated with this low-pressure system started showing up Thursday in Baton Rouge and New Orleans. This rain and higher winds will be impacting Louisiana through the weekend and maybe into next week.

Barry Keim, Louisiana state climatologist, said not only will there be rain in Baton Rouge for several days, but the winds are expected to reach 20 to 30 mph, with higher gusts. That could mean the possibility of falling trees or power lines, he said.

Winds were starting to pick up Thursday evening and are expected to get stronger Friday, he said.

How long these conditions will continue is uncertain: some forecasts show the system affecting the Louisiana area for three to four days while other show it could last up to seven days.

That could mean that some areas of Louisiana could see up to 10 to 20 inches from the rain bands put off by this system, he said.

Exactly where the system will go once it does start moving also is uncertain.