Watching the Gulf: What We Know About Potential Tropical Development

Good morning Foothills Weather followers. I want to come on this morning and give everyone an update on the Atlantic tropical season and, more specifically, the potential for tropical development in the Gulf of Mexico later this week.

There is going to be a lot of model talk surrounding this over the next several days, so I want to get out ahead of it and explain what we are actually watching and what it could eventually mean for Western North Carolina.

Right now, a tropical wave is moving westward across the western Caribbean at around 15 mph. The National Hurricane Center notes scattered showers and thunderstorms associated with this wave. At the same time, we already have a fairly complicated weather pattern developing across the Gulf. Moisture is being transported northward out of the Caribbean, while a deep-layer trough is influencing portions of the eastern Gulf.

This becomes more interesting as we move through the upcoming week.

A cold front is expected to move south toward the northern Gulf Coast and eventually stall across the northern Gulf. Behind that front, northeast to east winds are expected to increase, while the overall pressure pattern across the Gulf changes considerably.

That stalled frontal boundary could become very important to whatever happens with the tropical disturbance.

If we end up seeing a more organized area of low pressure to develop and move northward through the Gulf, the environment farther north becomes increasingly hostile. Stronger upper-level winds and increasing wind shear associated with the trough and frontal boundary would work against a tropical cyclone maintaining a vertically stacked circulation.

Before reaching that more hostile environment, however, there may be an opportunity for strengthening if a closed circulation develops and the system spends enough time over the warm Gulf waters. I think a stronger tropical storm is within the realm of possibilities, and we cannot completely rule out hurricane strength if the atmospheric environment becomes favorable enough for a period of time.

That is far from a forecast at this point. We don’t even have a developed tropical cyclone yet.

As the system moves farther north, increasing shear could begin pulling the thunderstorms away from the low-level circulation and substantially weaken or even destroy its tropical structure. But that doesn’t necessarily mean the entire weather system simply disappears.

A residual surface low and a tremendous amount of tropical moisture could continue north or northeastward and eventually become incorporated into the larger mid-latitude weather pattern.

That’s the part of this that matters to us in Western North Carolina.

If the eventual low tracks well west of the southern Appalachians, roughly toward the lower Mississippi Valley before lifting northward, Western North Carolina would likely remain on the eastern side of the broader circulation. That could bring an increase in tropical moisture and potentially some heavier rainfall, but that type of track by itself would not automatically translate into widespread flash flooding across our area.

A farther-east track through portions of Mississippi, Alabama and Tennessee would get my attention considerably more.

That type of track could place Western North Carolina closer to the deeper tropical moisture plume and potentially provide a better setup for widespread heavy rainfall. Terrain interaction along the Blue Ridge and eastern escarpment would then become increasingly important. Depending on the low-level wind direction, moisture transport and forward speed of the system, the risk for localized or more widespread flooding could increase.

Those are scenarios, though—not forecasts.

There is a tremendous amount that has to happen between where we are this morning and any potential impacts here next weekend or beyond.

I also want to address the computer models because you’re probably going to start seeing individual model runs posted all over social media.

The models have struggled with the pattern we’ve been dealing with recently. The Pacific flow has been extremely active and complicated, and that has made resolving individual shortwaves, trough evolution and downstream amplification difficult at longer ranges. Small differences upstream can become very large differences several days later across the Gulf and eastern United States.

Both of the major global modeling systems have been showing some version of Gulf development, followed by a movement northward into a progressively more hostile environment. Beyond that broad idea, there are significant differences involving timing, forward speed, intensity, track and how well the circulation survives its interaction with the trough, frontal boundary and increasing wind shear.

Those differences matter enormously.

A 100- or 200-mile change in track several days from now could mean a completely different rainfall setup for Western North Carolina. The forward speed matters just as much. A weakening system moving quickly through the Tennessee or Ohio Valley presents a much different rainfall scenario than a slower circulation transporting deep tropical moisture into the southern Appalachians.

So I don’t want anyone looking at one model image eight or nine days into the future and treating it like a hurricane forecast.

It isn’t.

And I want to be especially clear about something else: at this point, I see no reason to compare this potential system with previous storms that produced devastating flooding across Western North Carolina.

We don’t have evidence supporting that kind of comparison right now.

Could we eventually receive heavy rain from whatever develops? Absolutely.

Could the forecast change substantially over the next several days? Absolutely.

Do we currently have enough information to tell you that Western North Carolina is facing a major tropical flooding event? No.

Not even close.

For now, we watch.

First, let’s see whether we actually get organized tropical development. Then we determine how strong the system becomes. After that, we watch its interaction with the stalled front and increasing wind shear over the northern Gulf. Only once those pieces begin coming together will we have much confidence in where the remnant circulation and tropical moisture ultimately go.

I’m getting this information out early because I’m sure some weather pages will soon start posting the most dramatic model runs they can find. Don’t let a seven-, eight- or nine-day computer model image play on your emotions.

Our team at Foothills Weather Network will continue doing what we’ve always done: watch the pattern, look at all of the data, explain what is changing and give you a clear and calm assessment of the realistic impacts to Western North Carolina.

Right now, this is something to watch—not something to worry about.

We’ll keep you updated as the picture becomes clearer.