What's causing the high-impact coastal flooding along the East Coast this weekend?

AccuWeather

AccuWeather's Geoff Cornish explains all of the factors leading to the severity of effects expected from an ongoing tropical wind and rainstorm.

Transcript

00:00Well, we do have a lot to talk about with a high-impact weekend storm. I want to show you

00:07some of the factors at play that will be driving the coastal flooding that makes this storm a one

00:12on the AccuWeather real impact scale for hurricanes. It may not officially be technically

00:17a tropical system in terms of meeting the definition for a named storm within the

00:23government's eyes, but it's about the impacts that we're concerned about, and that's what

00:26we're calling as a tropical rain and windstorm. And it will eventually take on some quasi-tropical

00:31characteristics later in the storm's life cycle. But right now, as we take a look at the big picture

00:35here, we have the formation factors. There's a big puddle of cool air under this upper-level

00:41low-pressure system, and the water temps just off to the east side of Florida are 81, 82, 83 degrees.

00:47So as this puddle of cool air with this big dip in the jet stream slides east, it begins to camp out

00:53over that warm water. And under that, we get this little low-pressure system to begin to spin up,

00:59and it becomes a much more impactful storm. So this is going to ramp up here, and by Saturday night,

01:05low-level wind circulation will be like this. Here you can see the wind at about 20,000 feet.

01:12Those winds are going to be driving the storm. The steering influences will be driving it northward

01:16here into the Outer Banks. So big picture, here is our AccuWeather tropical eyepath for this storm.

01:23And we're very concerned because this is going to be taking its good old time pulling north.

01:28Saturday afternoon and evening, Sunday afternoon and evening, Monday afternoon and evening.

01:32Anytime you're north of the center of this storm, anybody north of the center of the storm,

01:36you're going to have that strong onshore wind, which is going to be driving ocean water inland.

01:42And that's going to be producing coastal flooding. So again, anybody north of the center of the storm,

01:47you're facing that onshore wind. And as we ramp up here, Saturday, gusts of 30 to 40 miles per hour.

01:54Today we've had gusts even before the storm forms, over 20 to 30 miles per hour farther south.

01:59But tomorrow, this begins to ramp up late Saturday. And the big driver here is the coastal storm,

02:05our tropical rain and windstorm. But there's also a massive factor at play in the form of a strong

02:10high pressure system over eastern Canada. So these are working in tandem with one another,

02:16a tight pressure gradient driving this problem, major problems here with coastal flooding.

02:22Let's look at the models here. And this forecast here, the GFS, I wanted to point out,

02:28we have another player on the field. Here's your upper level low. That's the big driver in getting

02:32this going. But there's also this other pesky system crossing the Great Lakes. And the interaction

02:37between that system and the coastal low will dictate how Sunday shapes up. Now the GFS model,

02:45this is the American model, this is a little more aligned with most computer models out there.

02:49And this is the main, this, among two examples I'm going to show you, this aligns pretty well with

02:55our forecast here. Sunday night and Monday, you can still see that interaction between the two.

03:01It's kind of an elongated, stretched out zone here. But the coastal storm at the surface will be

03:06spinning its wheels east of Virginia. And that Great Lakes low interacts with the trough and the

03:14long wave trough, the big trough across the east coast in such a way that it will ultimately

03:17strengthen the storm system, but also probably hold it back a little bit in terms of longitude,

03:22keeping it near the coast for a time. And then a chunk of energy rotates around the base of it

03:26and it carries it out to sea. Now the European model is a bit different. You can see

03:31there's a break here within the, the, the thickness lines here. They don't quite connect

03:36here Sunday morning like they do in the, in the GFS. So the storms are a little more separate for

03:42longer, even into Sunday. So that plays a role in the European depiction of events, keeping this

03:50a little more separate. And ultimately that impacts Sunday. So Sunday, here's the GFS model. We think

03:56this is the most likely scenario. And this aligns pretty well with our forecast. Strong onshore

04:01winds, rain in New York City and so forth. But take a look at the European at the same time,

04:05not even raining in New York City because these two surface low pressure systems are actually

04:11separate. They're not really consolidated into one as cohesively. So we need to keep an eye on this

04:17as a potential. But even if the European is right, it backs rain into Long Island and New York City late

04:23Monday. And then Tuesday morning, while the GFS is winding down, the European still fairly strong

04:30just off the Jersey shore. And then it eventually goes out to sea. So it's kind of an interesting

04:34scenario that there are still a few questions when we're honest about this on the table about how

04:39Sunday night and Monday play out. Significant wave heights. This is the wave watch model. I just

04:44wanted to briefly show you some areas with 20 plus foot wave heights off the Jersey shore. That's a big

04:48deal out there. And again, that's offshore. Now, as we bring it back to the models, or back away from

04:53the models to our forecast. Again, we can't just show you models and say, well, this is what one

04:58model says. This is what another says. Have a great night. We have to make an actual forecast. And we're

05:02hedging toward this. Again, the storm hugging near the coast, strong onshore winds and rain. We're likely

05:10to see rain in New Jersey and even in New York City on Sunday evening. We're hedging toward that first

05:16depiction that I showed you. We have a storm surge of one to three feet in many areas. But I do want

05:20to point out our AccuWeather local storm acts. It's conceivably in an extreme case, somebody out

05:25there could see a potential surge of more than three or four, maybe even more than five feet.

05:31It's more likely that most of us see one to three foot storm surge. But somebody out there like

05:35Lewis, Delaware, here's a candidate for more than three foot storm surge. This is based on

05:40NOAA. It's an experimental product that's been around since the late 90s, improved slightly since then.

05:45But NOAA has an extra tropical storm surge model. That's what they call it. And here's your, the light

05:54blue is your typical high tide based on the moon's influence of around two and a half feet in Lewis,

05:59Delaware. Look at this model's projection. That is more than four feet. That's actually four and a half

06:04feet above the typical tide because of massive, massive flooding from that onshore wind. That would be

06:10Sunday midday and then Sunday midnight to the early morning hours of Monday morning. So those are some

06:16concerns that we're tracking coastal flooding with our forecast feet.

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