Millions brace for impact as Tropical Storm Sally gains strength

The storm is expected to slow down right before landfall in the South, prompting water evacuation preparations and mandatory evacuations in low-lying areas.
4:10 | 09/14/20

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Transcript for Millions brace for impact as Tropical Storm Sally gains strength
We begin with tropical storm Sally taking aim at the gulf. The satellite of the powerful storm which is expected to intensify and reach hurricane status tonight, robin. And the governors of Mississippi and Louisiana declaring states of emergency. New Orleans is under a hurricane warning. Ginger is there now with where the storm is heading and that major storm surge concern. Good morning, ginger. Good morning, robin. From here Toour family in pass Christian to pascagoula and even even mobile. It could be the fourth of the year which is unbelievable to think. See it on the image there. Less than 200 miles to my southeast standing along the Mississippi but the worst of the impacts as it makes landfall tomorrow and before will be that surge and heavy Rhine to the right of this storm so this could be a very heavy on the coast of Mississippi storm that we're talking about. That's W we have rob Marciano right there in biloxi this morning. Hey, good morning to you, ginger. As you said 18 named storms so far this year, so many of those hitting the U.S. Three of which hitting the northern gulf coast just in the last three weeks. This as we mark the 15-year anniversary of hurricane Katrina which brought a 28-foot storm surge engulfing much of the lighthouse one of the few things to survive that storm and now here comes another hurricane. Power is going out right now. Reporter: Tropical storm Sally gaining strength taking aim at the gulf coast. The storm already bringing a foot of rain in the keys causing major street flooding. Saturday one of the wettest days the area has seen in 15 years. Residents in Mississippi and Louisiana bracing for impact as the storm is expected to slow down right before landfall and torture the region for several days. It's better to be safe than sorry, get your vessel out. Reporter: In by lox, Mississippi, long lines of boats waiting to evacuate to safer waters. Both states have declared states of emergency. Mandatory evacuations ordered for low-lying areas of Hancock county, Mississippi and grand isle, Louisiana. Everybody should take this seriously. Please understand that you should be moving now, acting now to get you and your family ready for the storm. Reporter: Taking a similar path as hurricane Katrina 15 years ago. New Orleans expected to take up to 20 inches of rain and a life-threatening 121-foot storm surge. The city's levees will be tested. I got a firsthand look at the improved levee system a few weeks ago and then there's this wall. New since Katrina just east of New Orleans designed to keep any gulf surge out of the city. It is huge. 26 feet high and nearly two miles across. And with the track of this storm, we're going to see persistent northeast winds which means water being pushed up against that barrier for multiple tide cycles. It will be tested for sure. Here in biloxi we expect a nine-foot storm surge which means the lighthouse will survive but probably won't be broadcasting from this spot tomorrow. To say this is storm weary is an understatement. We're just halfway through. I know. I'm so glad that you said that, that it's going to be a little slower than some of the storms we've seen already. That is going to be impactful not just with the heavy rain that could approach two feet in some places, but especially with the surge so here's the surge forecast, a detailed look at kind of far eastern Louisiana where you've seen nine plus feet. Six feet then three feet along lake pontchartrain. Why do we always have this issue? The east coast to explain it, the falloff of the continental shelf acts as a barrier so if you have surge 2 can absorb some of it. The gulf coast, a much more gradual incline up to the beaches so that surge or bubble of water that comes up when you've got six feet, it reaches far inland. That is why here along the gulf coast we are concerned even when we see three feet of surge. So much concern out there. So glad you're warning everyone. Thank you.

This transcript has been automatically generated and may not be 100% accurate.

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