Monday, September 10, 2018

Hurricane Florence Update:A Behemoth Takes Shape; Mega-Flooding Possible, But When and Where Will a Temporary Inland Sea Form??

NOTE: I composed this entry last night (Monday) but didn't post it until Tuesday early afternoon. However, I am not updating it. Instead, I will post new information later tonight.

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A monster slides into view …

GOES 16 color view at 1712 UTC Sept 10, 2018 with Hurricane Florence just coming into this satellite's view.

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I'd like to post a comprehensive update on Hurricane Florence, but there is just so much information about model runs and potential scenarios -- most producing disastrous-to-catastrophic flooding somewhere between South Carolina, interior North Carolina, the central Appalachians, or even here in the D.C. area -- that it's hard to focus and get it written.

NWS/NCEP/WCP's 7-day precipitation total forecast for the "DMV" -- District of Columbia and adjoining parts of Maryland and Virginia -- through 8 a.m. Sept 17, 2018.

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In addition, there are several days to go and lots of model runs and much analysis even while there are already evacuations and emergency preparations underway along parts of coastal North Carolina and in the Hampton Roads / Tidewater area.

As of 5 p.m. EDT, Hurricane Florence is has resumed its category 4 strength after days of having weakened to a tropical storm and minimal hurricane. That is, the forecasted / anticipated rapid intensification has happened.

Here is the 5 p.m. EDT 9/10/2018 NHC update

Location: 25.4 N, 61.1 W or 525 miles SSE of Bermuda and 1170 miles ESE of Cape Fear, North Carolina
Maximum sustained winds: 140 mph
Central pressure: 939 mb or 27.73" Hg
Present motion: WNW / 285 degrees at 13 mph

From the 5 p.m. EDT NHC discussion:

Florence has recently turned west-northwestward, still moving at 11 kt. The hurricane is expected to accelerate in that direction over the next day or two due to building mid-level ridge over the northwestern Atlantic Ocean. By late Wednesday, a turn toward the northwest is forecast due to the orientation of the Atlantic ridge, along with a decrease in forward speed due to a new ridge building over the Great Lakes.


12Z 10 Sept 2018 model run showing 7-day precipitation total (in inches) for a portion of the eastern United States, as prettied up by WxBell.com.

I think this is a GFS run but the image was specified. This would be a flooding disaster for North Carolina and northern South Carolina.

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There is a new player in the forecast as well, with the disturbance over the northwestern Caribbean adding some uncertainty in the ridge strength over the southeastern United States. Perhaps it isn't surprising that the model spread has increased on this cycle, with a small eastward shift overall. The official forecast is nudged in the direction of the trend, but is west of the model consensus. It is important not to focus on the exact forecast track as average NHC errors at days 4 and 5 are about 140 and 180 n mi, respectively, and dangerous hazards will extend well away from the center.

Spaghetti chart of all the major model tracks for Hurricane Florence in their 12Z Sept 10, 2018 runs.

This image and two more below (noted) are taken from Cranky Weather Guy's posting about the hurricane which you may read here. Of note, "FV3" represents the latest iteration of the GFS. It is distinct from the current operational GFS.

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About this ridge, I'd like to note this CWG entry (link embedded): Hurricane Florence could be a lot like Harvey. Here's why.

This entry contains the following animated plot of 500 hPa (i.e., 500 mb) height percentile anomalies between hours 0 and 102 initialized from the GFS 12Z 9/9/2018 versus the three-week climatological 500 hPa from the Climate Forecast System Reanalysis (CFSR) for the period 1979 - 2017. This runs from 12Z 9/9/2018 through 18Z 9/13/2018.

Caption: This plot compares forecasts from the American (GFS) model with average conditions over a three week period. By Thursday, the forecast calls for a high-pressure system that would be the strongest for this time of year over the past three decades. (Tomer Burg) (Greg Porter/Washington, D.C.)

What this is showing is that Florence is going to bump into and slide under a large, anomalously strong ridge that extends over the eastern U.S.

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Upper level pattern schematic (labeled) from Cranky Weather Guy, Sept 10, 2018

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Before I post this, I should note that Cranky Weather Guy (relevant entry linked above) has a different take on this that can be summed up as follows: The ridge north of the hurricane will not be as strong / extensive as forecasted and the weakness left by what was Tropical Storm Gordon last week might allow the storm to stall offshore and be shunted out to sea. The height / pressure field weakness left by Gordon is the "new player" referenced in the NHC write up.

Hurricane Florence and schematic of the atmospheric streamline pattern (labeled) over the western Atlantic on or about Sept 12, 2018;
Source: Cranky Weather Guy Sept 10, 2018 posting.

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In the case of the Euro model, is has an even stronger ridge -- hence the storm coming ashore around Cape Fear, N.C., and stalling over North Carolina. He is disagreeing with that model output and he gives his reasons. At least I think that's what he's saying.

12Z 10 Sept 2018 European model's precipitation totals (in inches) for the "DMV" -- District of Columbia and adjoining parts of Maryland and Virginia -- between hours 72 and 192.

This would be a disastrous situation for flooding across much of Virginia.

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GOES 16 satellite image loop between roughly 2300 UTC 10 Sept and 0200 UTC Sept 11, 2018.

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Here are two more CWG entries:

'Extremely dangerous' Hurricane Florence may approach Category 5 as it churns toward the Carolinas

Note: This entry has been updated multiple times -- including the title -- and so if you click on it, the entry may appear differently. I wish CWG wouldn't do that but instead post a new entry.

What will Hurricane Florence mean for the Washington area?

This entry is where I got the first "DMV" rainfall map above.

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As a brief personal update …

A sad-looking, rain-soaked sunflower, Ontario Rd NW, Washington, D.C., 3:04 p.m. Sept 9, 2018

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Yesterday (Sunday), I did almost nothing except go grocery shopping at Harris Teeter in Kalorama. Well, I also showered/shaved and did regular ablutions. It was quite a rainy day.

The cast of 'Allo 'Allo!

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Around 9 p.m., I went next door to Fred and Doug's place in the Northumberland and we watched two more Netflix-carried episodes of the frickin' hilarious British comedy 'Allo 'Allo! We've been slowly cycling through the show's 85 episodes -- presently at the start of season 4.

It was - as I noted in my previous entry -- a cool and pleasant one with temps around 60F.

Blurry rainy night view, New Hampshire Ave and 21st St NW, Washington, D.C., 12:29 a.m. Sept 9, 2018

I had met Tim at Circa DC and was walking home.

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Tonight, by contrast, is muggy and unpleasant -- at once drizzly wet and also uncomfortably warm and humid (around 75F with a dew point about 72F). And the city stinks of its usual smells that I can't abide. However, I'm ensconced in my little apartment, dim lamps lit, MeTV tuned to old shows, and air conditioner cranked up to make it chilly in here.

Stuffed animals including plush hippos.

I had the overhead light on just so the picture would take -- otherwise, nothing would have come out.

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For tomorrow night, I'm going to try to go to the gym. I will try to post an entry later Tuesday night or early Wednesday morning.

--Regulus

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