Saturday, September 8, 2018

Suddenly, Cool and Wet; Preliminary Overview of Forecasted Major Hurricane Florence, Possible High Impact on U.S. East Coast Next Week

View of the George Washington Masonic Nat'l Memorial and surrounding area, Alexandria, Va., Sept 8, 2018

Tim sent me this picture earlier today -- one of a dozen or so weather and picture ones he has sent me in the past few days.

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Saturday afternoon.

Finally, the hot, humid weather has broken.

Today is an overcast gray, showery, much cooler day with air temps around 72F. It remains quite humid (dew point about 66F). There is a decent area of rain north of the region across Pennsylvania but still some scattered rain showers / downpours in the D.C. and Baltimore areas.

Sterling (LWX) NWS radar in standard base reflectivity looped 1:27 p.m. - 2:03 p.m. EDT Sept 8, 2018

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Tomorrow is forecasted to be outright rainy, although today is turning out to be wet, too.

The big news is a developing weather story by the name of Hurricane Florence.

Colorized infrared satellite loop of Tropical Storm Florence earlier today, Sept. 8, 2018 (unsure of time).

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Well, actually, right now it is a tropical storm -- having gotten up to a borderline category 4 tropical cyclone earlier in the week way, way out in the Atlantic Ocean before weakening significantly due to an atmospherically unfavorable environment (wind shear and dry air entrainment).

Streamline visualization for Hurricane Florence on Wednesday, September 12, 2018

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However, the National Hurricane Center (NHC) is almost certain that Florence is going to re-intensify into a major hurricane (category 3 at least) by early next week even as it continues on an extended west-northwesterly path that brings it near the U.S. East Coast in the Wednesday - Friday timeframe of next week.

Caption from CWG entry (linked below): Group of simulations from American (blue) and European (red) computer models from Friday. Each color strand represents a different model simulation with slight tweaks to initial conditions. Note that the strands are clustered together where the forecast track is most confident, but they diverge where the course of the storm is less certain. The thick bold red line is the average of all of the European model simulations, while the blue is the average of all the American model simulations. The thinner bold (red and blue) lines are the main or operational simulations from each model. (StormVistaWxModels.com)

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As shown in the image directly above, the European model and its ensembles have suggested a Southeast or even Mid-Atlantic landfall while the GFS and its ensembles have tended to show more offshore recurvature. A few days earlier, these tracks stayed mostly offshore.

NWS NHC five-day track / cone of uncertainty for Tropical Storm Florence along with expected strengthening to a major hurricane ("M"); Advisory 37, 11 a.m. AST September 8, 2018.

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NHC's five day track (see image directly above) is beginning to hone in on a South Carolina landfall, but we are still 6 days / 144 hours away from that with lots of time for things to change.

Band 13 - 10.3 ┬Ám - Clean Longwave Window - IR - 08 Sep 2018 - 1745 UTC, Atlantic Ocean.

Florence is way out there on the right.

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As of 11 am AST, Tropical Storm Florence is centered at 24.5°N 54.3°W (835 miles SE of Bermuda or 715 miles NE of the Northern Leeward Islands) with a westward movement at 7 mph. Minimum pressure is 995 mb (29.39") and maximum sustained winds at 65 mph.

Again, this system is forecasted to undergo a rapid strengthening by Monday.

Here is a new Capital Weather Gang article on it with lots of imagery / graphics:


OK, I need to hurry up and get ready and go. Despite the less-than-ideal-picnic-weather, our company is having its annual picnic at a place up in Silver Spring just north of the Glenmont Metro. Maybe it'll be moved inside.

My plan is to post an entry tonight (although probably not a Jukebox Saturday Night entry for this week).

--Regulus

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