September 12: Too Much For One Headline

Weather
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WEATHER

Record heat, severe storms, a big temperature shift, more action in the tropics…there’s just a LOT going on! Let’s start with today’s near-record high temperatures — we’ll reach the low to mid 90s this afternoon.

Right now I think we’ll fall one degree short of the record in the Triangle, just two degrees shy in Fayetteville. Both records were set in 1983.

Not only will be it be extremely hot, but the humidity hasn’t gone anywhere.

The heat and humidity will combine forces to push the heat index into triple-digit territory — rare for mid-September!

A weak cold front will drop down from the north late today — as it encounters the hot and humid air mass, we’ll see a chance of scattered storms this evening and early overnight. The forecast model data is all over the place with this storm chance, though…a theme we’ll come back to farther down in the post. The HRRR model’s radar simulation from 11:00am through 11:00pm shows limited activity.

But the North American Model’s simulation in the same time frame is considerably more enthusiastic, showing more-widespread and stronger storms.

With that discrepancy in mind, I can’t be too confident in our rain chances — they’re a little higher than in yesterday’s forecast, but still lower than 50-50.

If (BIG IF) the storms get going, a couple could pose a brief damaging wind threat. The Storm Prediction Center has outlined a “Marginal Risk” (level 1 of 5) for almost all of central North Carolina.

I had to make some adjustments to Friday’s forecast as well — it looks like northeasterly winds will trap the clouds in place for most of the day, keeping highs in the Triangle around 80° and even the 70s to the north. Our counties along the southern Coastal Plain and in the Sandhills have a better chance of cracking the clouds, allowing temperatures to warm well into the 80s.

We’ll see some lingering off-and-on showers under the thicker cloud cover — where the sun breaks through, scattered storms will re-develop in the afternoon and early evening.

The clouds will probably be trapped in place through at least midday on Saturday — enough sun could peek through later in the day to warm things up to the mid 80s. Sunday returns us to the hot weather pattern, with highs around 90°. As for the long-range forecast…well, that kind of depends on what the tropics decide to do.

TROPICS

Things were looking “active, but okay” in the tropics in the wake of Dorian…until this morning. This was my reaction to the overnight forecast model data.

The area of disturbed weather near the Bahamas now has a much better chance of becoming at least a tropical depression. The National Hurricane Center gives it a 70% chance of that in the next 48 hours, an 80% chance over the next five days.

The shaded area on that map shows the NHC’s estimate of where the system will go…which brings us to the overnight model data, specifically the European forecast model’s ensemble. (That’s the same model run dozens of times with slightly different conditions, to give us a range of possibilities and hopefully a sense of the most-likely scenario). The ensemble shows a 90% chance that the system becomes a tropical storm over the weekend, still off the east coast of Florida.

From there, the various ensemble members mostly keep the system on the Atlantic side of the Florida peninsula, and move it north…sound familiar? The “spaghettios” animation shows each ensemble’s estimate of where it will go.

That’s a WIDE range of possibilities, but we’re obviously going to have to keep a very close eye on this system. If you want the worst-case scenario, the ensemble shows a 20% chance there’s a hurricane off the coast of the Carolinas by the middle of next week.

Let me be clear: that is NOT the most-likely scenario at this point. A 20% chance of that worst-case scenario gives us a big ol’ 80% chance of anything else.

What about the other model data? The UK forecast model is statistically the second-best in the world (behind the European) — it’s pretty much on the same page.

Canadian model? Same deal.

The American GFS model is holding onto hope — keeping the system weak, tracking it into the Gulf, then pushing it onshore as nothing more than a big glob of rain.

Problem is, the GFS is statistically inferior to the other global models…even after (some would say especially after) its “upgrade” earlier this year. I sure hope it’s right this time around, though…

Am I worried about this potential tropical system? No. Will I be watching it? Heck yeah. So will the National Hurricane Center — they’ll start issuing “potential tropical cyclone” advisories later today.

Farther out in the Atlantic, there’s another area of disturbed weather that has close to a 50-50 chance of becoming a tropical depression over the next five days as it tracks to the west.

It’s about a week away from potentially moving into the Caribbean, so we’ve got plenty of time to monitor this one.

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