September 4: Tracking Dorian


Today’s weather gives us the calm before the storm…there’s a reason that’s a famous cliché. It will be hot, despite increasing clouds overhead, and the humidity will be substantial. Highs will top out around 90° this afternoon.

The thickening clouds are associated with Hurricane Dorian, now spinning its way northward along the Atlantic coasts of Florida and Georgia. As of 11:00am, it’s still a Category 2 storm with 105 mph sustained winds.

Dorian is still moving over the very warm waters of the Gulf Stream, so some strengthening is still possible over the next 24 hours. Regardless of the specific wind speeds, the storm will remain close to its current intensity as it tracks along the Georgia coast toward South Carolina — by Thursday afternoon, the center of circulation will be just off the coast of Charleston.

From there, Dorian turns to the northeast, passing over Bald Head Island and just offshore from Wilmington. The storm will speed up as it heads towards the Outer Banks, moving off into the Atlantic by late Friday.

That path just tracks the center of circulation — of course, the storm itself is much larger, and the threats associated with the storm will extend well inland. Exactly how far inland will be determined by Dorian’s path — as I talked about yesterday, a track right along the coast would reduce the wind speeds, but spread out the heavy rain “footprint”.

The latest forecast model data has been trending very slightly closer to that right-along-the-coast scenario. This is the radar simulation from the North American Model from noon Thursday through noon Friday.

That kind of setup would push heavier rainfall amounts as far west as the Triangle, and the newest rainfall outlook from the Weather Prediction Center reflects that.

WPC Precipitation Estimate

That’s an absolutely crazy transition zone, right over central North Carolina. I mean, look at the numbers…less than an inch in Chapel Hill, and over seven inches in Goldsboro? Now you know why I’ve been hammering the point: a small change to the forecast will result in a BIG change to impacts in central North Carolina!

Some of the forecast data maintains that the heaviest rainfall will remain close to the coast. This is the European forecast model’s estimate.

European model forecast

Other models spread that heavy rain significantly farther inland, bringing the flooding threat almost to I-85. This is our RPM model — pretty close to the worst-case scenario for this storm.

RPM model forecast

The National Weather Service has issued a Flash Flood Watch for the southeastern half of central North Carolina.

The Weather Prediction Center’s “excessive rainfall outlook” shows a rare High Risk of flash flooding just to our south. That could be expanded into central North Carolina if Dorian shifts just a little bit.

The wind will be another factor we have to deal with, but the greatest potential for wind damage and widespread power outages will remain closer to the coast. We expect sustained tropical storm force winds (39+mph) along and east of I-95 by Thursday evening into Thursday night, with tropical storm force gusts elsewhere.

To account for the wind damage potential, a Tropical Storm Warning is in effect — it’s been slightly expanded as it was upgraded from a Tropical Storm Watch, and now includes Wake county.

Averaging out the discrepancies between the various forecast models, here’s the overall impact pattern we expect across central North Carolina.

Significant flooding and numerous power outages will be more common in out southeastern counties, while locations west of I-85 will likely dodge any major effects. The Triangle and all other areas between I-85 and I-95 are in that sharp transition zone — every mile you travel to the southeast will bring you into heavier rain and stronger winds. And of course, this pattern will shift along with any shift in Dorian’s path.

1) It’s going to rain, it’s going to be windy.
2) The nastiest conditions — heavy rain and strong winds — will arrive by Thursday evening and continue into early Friday morning.
3) The forecast track could still shift, and any small change is a big deal.
4) Flash flooding and power outages will be the main concerns late Thursday into early Friday, river flooding will be a concern into the weekend.
5) If you live in a flood-prone location, ride this one out somewhere else…especially along and east of I-95!
6) Make sure your cell phone is charged and you’ve got batteries handy.

We’ll be here tracking the storm! I’ll be on Twitter posting updates whenever I’m not sleeping…

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