eye on the storm

September 3: Dorian Headed Our Way

Weather

11:45AM UPDATE: Dorian is now a Category 2 hurricane, with 110 mph sustained winds. I outlined why I thought the storm would be downgraded in this morning’s original post (below). The NHC forecast shows Dorian maintaining that strong Category 2 strength as it tracks up the coast.

Since Dorian will be traveling over the warm water of the Gulf Stream and into a low-wind-shear environment, I still think it’s very possible the storm strengthens to Category 3 again. The forecast track along the North Carolina coast is largely unchanged, so what I wrote below about wind and rain impacts in central North Carolina still stands.

The southeastern half of central North Carolina is now under a Tropical Storm Watch until further notice (basically, through Friday morning). The strongest winds within the watch will be farther to the southeast.

Stay tuned for more updates!

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POSTED 8:30AM: Before Dorian impacts our weather by Wednesday night and Thursday, it will just be hot and humid today and tomorrow. Highs this afternoon will top out in the upper 80s to around 90°.

Just a very slight rain chance this afternoon, mainly east of the Triangle — the HRRR model’s radar simulation isn’t impressed.

We’ll see gradually increasing clouds on Wednesday as Dorian finally starts to make its way up the Frorida, Georgia and South Carolina coasts. Temperatures will still reach the mid to upper 80s before the clouds really thicken up.

HURRICANE DORIAN

Dorian has hardly moved over the last 24 hours — it’s parked just north of Grand Bahama island, with 120 mph sustained winds as of 8:00am.

The storm has weakened over the last 36 hours, because of its nearly-stationary status. The violent winds have pushed around the warm upper layers of the Atlantic, which prompts “upwelling” of cooler water from under the surface…basically, Dorian is cutting off its own energy source. But the storm will start to move north today, over the warm waters of the Gulf Stream — so even if it weakens to Category 2 strength briefly today, it will likely re-strengthen to major Category 3 strength tonight and tomorrow.

The storm will start turning to the northeast Wednesday night, running just off the North Carolina coast Thursday, until it hits the Outer Banks Thursday night as a Category 2 storm.

The “cone of uncertainty” still includes both the possibility of a coastal or slightly-inland track, and the possibility of a turn into the Atlantic. The odds that Dorian takes a path inland of the coast are decreasing, but not zero…and it’s still possible that the storm takes a harder right turn and heads out into the Atlantic.

The forecast model data is in good agreement overall with the NHC’s forecast path. As tightly clustered as these projected tracks are, they still spell a world of difference for the impact on central North Carolina!

We’re getting to the point where some of the short-range forecast models are giving us a glimpse of Dorian moving up the coast. The North American Model’s radar simulation from noon Wednesday through noon Thursday shows the outer rain bands moving in from the south late Wednesday. That rain steadily progresses northward, and becomes heavier in our southern counties by midday Thursday.

As Dorian tracks along the coast, tropical storm force wind gusts (39+mph) become more likely to the south and east of the Triangle, which could result in sporadic power outages. Coastal North Carolina will be more likely to experience gale force (58+mph) or hurricane force (74+mph) winds.

Dorian’s greatest threat for central North Carolina will be the heavy rain that could lead to localized flooding. We’re going to be squarely in the transition zone between “not much rain” to the west of I-85, and “WAY too much rain” along the coast. The Weather Prediction Center (the NOAA branch that works in conjunction with the NHC in cases like this) predicts less than 1″ of rain to the west of I-85, with 2″-4″ along and east of I-95, and up to a foot of rain right along the coast.

Combine the wind threat with the heavy rain/flooding threat, and the greatest impact from Dorian will be felt along and east of I-95. Red-shaded areas on this map should be prepared for the possibility of power outages and some flooded roads. Orange-shaded areas aren’t likely to experience widespread power outages or flooding, but any TINY northwestward jog to Dorian’s path would increase the threat dramatically.

The wild card here is Dorian’s potential interaction with land as it moves up the coast. The center of circulation will stay offshore, but the western edge of the storm will drag over Florida, Georgia and South Carolina today and tomorrow. The friction with land will gradually slow the hurricane’s maximum sustained winds, but that means the area of heaviest rain will spread out even more. (Stronger winds would keep the heaviest rain “wrapped up” closer to the core.) That spreading-out of the heavy rain threat is what made Hurricane Matthew so dangerous as it scraped the coast in 2016. Dorian’s forecast path is farther off the coast than Matthew’s track, but still WAY too close for comfort.

Here’s the bottom line for today:
1) Coastal North Carolina will bear the brunt of this storm, with damaging winds, significant storm surge, and very heavy rain all likely.
2) Dorian will impact central North Carolina’s weather Thursday and Thursday night, but the severity of that impact will depend on the precise path the storm follows up the coast.
3) Any small change to the path could result in a much larger change to the impacts in central North Carolina. (For instance, a track 5 miles closer to the coast could spread the flooding threat 20 miles farther inland.)

Make sure you continue to check back for the latest forecast — we’ll be monitoring the data for any potential changes. We’ll be on TV during our regularly scheduled newscasts, along with quick updates at 11:00am and 2:00pm when the NHC posts its new track forecasts. And you can follow me on Twitter, Facebook and Instagram for more updates over the next few days.

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