August 24: Heat and Humidity Return, Daily Links

WEATHER

Two big stories in the weather today: the return of the steamy weather around here, and the potential development of a tropical system that could threaten the U.S. coast.  We’ll start with the local perspective, which actually isn’t too complicated: it will be hot.  And muggy.  For a while.

Today’s highs will reach the low 90s, with a mix of clouds and sun overhead:
WEDNESDAY HIGHS
Dew points are back up to around 70:
PAUL RPM 4KM DEW POINT
Which pushes the heat index up to the upper half of the 90s:
WEDNESDAY HEAT INDEX
Just an isolated storm chance today, as the HRRR model shows:
hrrr_2016082412_ref_nashville
It looks like the best storm chance will shape up along the Cumberland Plateau, but even there you’re not likely to get any free lawn-watering.

More of the same tomorrow, over the weekend, and into early next week:
WSMV 7 Day AM
The best chance of storms Friday and Saturday is just a one-in-three chance, so don’t cancel any outdoor plans based on that.  Just be ready to adjust if you have to, and be ready to deal with the heat and humidity!

Over the next few days, you’ll be hearing plenty about “something brewing” in the tropics — at this point, it’s just a tropical wave (that means it’s a disorganized glob of showers and thunderstorms).  If it gets organized, it will be categorized as a tropical depression, at which point it gets a number…if the winds strengthen to 39mph, it will be upgraded to a tropical storm, at which point it gets a name (next name on the list is Hermine).  If the winds reach 74mph, it will be upgraded to a hurricane.  The key word in all of that is “IF” because it’s still a disorganized glob of showers and thunderstorms right now:
PAUL SATELLITE TROPICAL
The National Hurricane Center estimates a 60% chance that it will become at least a depression within the 48 hours, and an 80% chance within the next 5 days:
two_atl_5d0
The range of possibilities with this system is all over the place — the “spaghetti plot” of the various forecast models shows decent short-term agreement regarding where the center of the system will go over the next few days (but those models aren’t in agreement as to the strength of the system in that time frame):
PAUL TROPICAL SPAGHETTI 1
After 72 hours, the computers just go to the zoo.  Does it go into the Gulf?  Does it stay off the East Coast?  The various models do both, and everything in between:
PAUL TROPICAL SPAGHETTI 2
But there are even more questions!  Does it stay a minimally-organized rain-maker?  Or does it develop into a hurricane?  The European forecast model has been painting an ominous portrait of a strong hurricane in the Gulf of Mexico by next week (the exact placement has varied from run to run, but the overall theme of “uh oh” has been consistent):
EURO
Meanwhile, the American GFS model shows…well, nothing much:
GFS
The European model is, on a consistent basis, more accurate.  In “model school” it drags the GFS out behind the gym and beats it up, steals its lunch money, then makes fun of its mom.  But that doesn’t mean it’s perfect — far from it!  We’re talking about a forecast that’s looking 120-180 hours in the future…that’s an eternity when you’re talking about simulating something as chaotic as the atmosphere.  The model accuracy scores in that time frame aren’t good for any model — in fact, it’s more appropriate to say that the European model is just “less bad” when it comes to forecasting weather patterns a week in advance.

All of which is to say: there could be trouble brewing for Florida and the Gulf Coast late this weekend and next week — I’m concerned about the fact that the more-accurate long-range model shows something close to the worst-case scenario, and I’m concerned about the fact that the water near the Bahamas and in the Gulf of Mexico is bathtub-warm.  BUT, at this point, there’s just as good a chance that this will fizzle.  We’ll adjust those odds as more data comes in…suffice to say, this one has our full attention.  One more round of “ifs”: IF it strengthens, IF it enters the Gulf, IF it becomes a hurricane and makes landfall, the soonest we’d see any remnant moisture around here would be next Thursday and Friday.  And that’s a looooooooooooooooooong way off.

 

LINKS

Plenty of weather stuff, as the tropics get more active.  Plus some other nerdiness as well…

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About paulheggen33

Morning meteorologist for WNCN-TV in Raleigh.
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