92L Gulf Low Pressure; What Does It Mean for Western NC Right Now?

Good morning Foothills Weather followers. I want to give everyone an update this morning on the system we continue watching in the Gulf and, more importantly, what it may or may not mean for us here in Western North Carolina this weekend.

First, I want to say this right up front: there is absolutely no reason to panic over this system. Nothing indicates another Catastrophic event for Western NC but there is also no reason to ignore it. There could still be some impact.

The disturbance we have been watching in the southwestern Gulf is becoming better defined, and the chance of tropical development has increased considerably. As of this morning, there is now an 80% chance of tropical development during the next couple of days. A tropical depression is likely to form as the system moves generally east-northeast before eventually beginning a turn toward the north.

A tremendous amount of uncertainty surrounding what happens after that remains. We are still missing a lot of data and will mot have it until upper air reconnaissance missions begin.

Until we have a well-defined circulation, we don’t have a true center for the models to initialize. Once a circulation develops and we begin getting better observations of the atmosphere surrounding it, the models should gradually get a better handle on the system.

Even then, another major piece of this forecast has to be resolved. There is a frontal boundary sitting across the Southeast and northern Gulf region, with a much drier air mass to its north and deep tropical moisture to its south. At the same time, an upper-level trough will eventually approach from the west.

How those three features interact — the tropical system, the frontal boundary and the approaching upper trough — is going to determine where this ultimately goes.

That is why I don’t want anyone getting locked onto an individual model run right now.

The graphic I’ve included with this post shows the three general scenarios I’m watching.

The GREEN line represents what I currently believe is the most likely general path. In that scenario, the system moves north from the Gulf and eventually gets pulled northward into the Lower Mississippi and Tennessee Valley region. That would bring tropical moisture northward into the Southeast and likely increase our rain chances across Western North Carolina this weekend.

The BLUE line represents the farther-west scenario. That would take the main circulation farther away from Western North Carolina. We could still receive rain as moisture gets pulled northward ahead of the system, but the axis of heaviest tropical rainfall would likely remain farther west.

The RED line is the least likely scenario but one that would concern me the most for Western North Carolina.

A farther-east track would bring the circulation and deeper tropical moisture closer to Georgia, eastern Tennessee and the southern Appalachians. That could establish a much stronger moisture feed into our mountains and foothills. If the low-level wind field were positioned correctly, terrain enhancement along the Blue Ridge and eastern escarpment could become a factor as well. That is still NOT another Helene, Francis, Ivan, or Hugo event.

That red line is NOT a forecast.

It is the scenario we need to watch because it would have the greatest potential to produce heavier rainfall and scattered flash flooding across our area.

And even with that scenario, I want to be very clear: I am not seeing another Helene-type setup.

I know that is where a lot of people’s minds immediately go anytime the words “tropical system” and “Western North Carolina” appear in the same sentence. After what our region has experienced, I completely understand why.

But every tropical system is different. The atmospheric setup is different. The moisture transport is different. The forward speed can be different. The position of the upper trough is different. The orientation of the low-level winds is different.

You cannot simply look at a tropical system coming out of the Gulf and assume the same outcome.

Right now, the more reasonable concern for our area is the potential for a period of rain this weekend, with the possibility of heavier rainfall depending on the eventual track.

There is increasing confidence that moisture will spread northward into portions of the Southeast, Tennessee Valley and southern Appalachians. What we don’t know yet is exactly where the corridor of heaviest rainfall will set up.

That distinction is extremely important. A track farther west could leave us with a fairly manageable rainfall event.

A track closer to the southern Appalachians could increase rainfall considerably and introduce a greater risk of localized flash flooding, rises on creeks and streams and some higher rainfall totals along the terrain.

There is a lot of real estate between those two outcomes. The other thing we’re watching is what happens when the system reaches the increasingly hostile environment farther north.

The system may have an opportunity to organize and strengthen over the Gulf, but as it moves north it will begin interacting with the frontal zone and stronger winds aloft. Eventually, it should begin losing its purely tropical characteristics as it interacts with the larger weather system moving across the country.

That transition is actually one of the biggest forecast questions. How quickly does it happen?Where does it happen?

Does the circulation remain intact long enough to transport a concentrated plume of tropical moisture northward, or does it become stretched and absorbed into the larger frontal system?

Those questions have enormous implications for where the heaviest rain falls.

The computer models still don’t agree on those details. Some are faster. Some are slower. Some take the system farther west. Others bring it farther east. There are also differences in how quickly the tropical circulation gets absorbed into the approaching trough. That tells me one thing very clearly: this forecast can change, and it probably will.

We’re still several days away from whatever ultimately comes north out of the Gulf. At this distance, moving the eventual track 100 or 200 miles east or west would make a substantial difference in our rainfall forecast.

So please don’t take the lines on my graphic as hurricane tracks or forecast cones. They aren’t. They are simply a way for me to show you the range of possibilities we’re evaluating this morning.

For Western North Carolina, I think the message right now is pretty straightforward. Enjoy the quiet weather through the end of the workweek. Expect our rain chances to increase this weekend. Understand that some heavier rainfall is possible.

And continue checking the forecast because we do not know yet whether the heaviest tropical moisture will remain west of us, move across us or end up farther east.

There is nothing in the data this morning that makes me believe people across Western North Carolina need to be scared of this system. There is enough in the data, however, that I’m paying close attention to it. You should too.

That’s the balance I want everyone to understand.

You are going to see model images floating around social media over the next few days. Some will show tremendous rainfall totals. Some will show very little. Some will take the low directly toward our region and others will take it hundreds of miles away.

Don’t let one model run scare you.

We’re looking at the entire atmosphere, not one colorful computer map. As we get a better-defined circulation in the Gulf, better observational data gets into the models and the upper-level pattern becomes clearer, we’ll begin narrowing these three scenarios down.

For now, GREEN is the general path we favor.

BLUE is the farther-west possibility.

RED is the scenario we don’t necessarily expect, but one we need to account for because it would bring the greater rainfall concern to Western North Carolina.

And once again, even the red scenario does not mean another Helene.

We’re going to keep this simple. No hype. No scary model maps eight days out. No trying to turn every tropical disturbance into a catastrophe.

We’ll watch it, we’ll follow the data, and when that data gives us a reason to change the forecast, I’ll tell you.

For now, keep an eye on it and go about your week.

We’ll have plenty of time to adjust if we need to.