Live from ABC News headquarters in New York City. This is Good Morning America.

Oh, good morning America. It is so good to see you on this Christmas Eve. What a show we have lined up.

Yeah. Getting in the holiday spirit here. Santa Claus, by the way, has a huge day ahead of him.

We are tracking the big guy's journey with Norad. We'll hear from the commander in charge of keeping tabs on St. Nick. That's coming up. Lots of him. We are tracking the big guy's journey with NORAD. We'll hear from the commander

in charge of keeping tabs on St. Nick. That's coming up. Lots of people looking forward to that,

but we do begin with a major flooding event in Southern California. After days of rain heading

the West Coast already, this morning torrential rain is taking aim, causing potentially

life-threatening flash flooding, especially in areas those wildfires devastated earlier this year.

We have team coverage this morning, starting with Melissa Don in Malibu. Good morning, Melissa.

Janae, good morning. We are already experiencing some of those heavy downpours here in Malibu,

and we want to show you just why the threat of rock slides, mudslides, such a concern. You see this hillside, that is a burn scar.

So just the force of this rain and the duration we're expecting could cause it to collapse.

This morning, after days of storms pummeling the West Coast, the urgent warning from officials pleading with residents to heat evacuation warnings and orders.

The last thing we want to do is ruin anybody's Christmas plans, but we have an obligation as a county family to wave the flag and say there's a threat, a real threat out there.

California already on edge after days of deadly rain, prompting several rescues from the air and the ground.

Life-threatening conditions possible with up to nine inches of rain expected, adding to concerns from fire-ravaged neighborhoods.

The heavy rains could trigger devastating mudslides. Residents in flood-borne areas have a plan.

Know what you're going to do when an evacuation order is given.

But in fire ravaged Altadena, they're taking no chances.

Here in Altadena, you see these empty lots from January's deadly wildfires.

As families work to rebuild right now, they're trying to protect what they do have

because the threat of mud

...