Louisiana Gov. John Bel Edwards says a “considerable” amount of water could over-top levees that hold back the Mississippi River in the New Orleans area as emergency officials prepared for a weekend storm.

That’s because the Mississippi River is already swollen from spring rains as a tropical weather system builds in the Gulf of Mexico and could add about 3 feet (1 meter) of storm surge to the river.

Edwards said at a Wednesday morning news conference that he intends to declare a statewide disaster later in the day. He said National Guard troops were preparing to be deployed across Louisiana with high-water vehicles.

Forecasters expect a broad area of disturbed weather in the Gulf to become stronger this weekend when it threatens the region with torrential rain.

Louisiana, Mississippi and Texas are all making preparations for heavy rain and possible flooding.

Forecasters expect a tropical weather system to develop into a storm that could push the already swollen Mississippi River precariously close to the tops of levees that protect New Orleans.

The low pressure area was over water, south of the Florida Panhandle early Wednesday and was expected to strengthen into a storm as it moved west through the Gulf’s warm waters.

Forecasters say parts of Louisiana could see up to 12 inches (30 centimeters) of rain by Monday, with heavier amounts possible in some spots.

Mississippi and Texas were also at risk of torrential rains.

The National Weather Service said New Orleans is protected to a river level of 20 feet (6.1 meters), but it was forecast to rise above flood stage to 19 feet (5.8 meters) by Friday.