Arthur

Post storm update, July 17, 1:44 p.m. Pacific: Arthur is long gone, having followed the forecast track rather closely. Here is a video of Arthur, as seen by hybrid infrared satellite imagery, put together by the National Weather Service:
 

NOAA

Arthur’s current five-day forecast cone from the NHC

Hurricane Arthur, per the NHC, will probably be a Category 2 storm when it reaches North Carolina’s Outer Banks. Then it will be in less favorable wind and water temperature conditions and should weaken as it accelerates rapidly to the northeast. Jeff Masters says that Arthur is unlikely to intensify into a Category 3 storm, thanks to dry air interfering with its eyewall.

The NHC issued its first-ever potential storm surge flooding map for this storm. Coastal residents as far north as the Delaware coast and the Chesapeake Bay should definitely check it.

Also, check out the local NWS office statements for Arthur now, if you live near or in Charleston, SC; Wilmington and Newport City/Morehead, NC; Wakefield, VA; and Boston, MA.

This local statement page will be modified for different areas northward along the coast as time passes. Per both the NHC and CHC, Arthur will be at its most intense during its passage off the coast from North Carolina to New Brunswick. It should be moving very quickly, but it will still cause a lot of heavy surf and coastal flooding along the nearby coasts. It’s then forecast to turn into a strong extratropical cyclone, and will probably go on to make life miserable for Newfoundland and perhaps Iceland and the UK next week.

 


July 2, 1:25 p.m. Pacific: I’m not sure Arthur is reading the NHC discussions. Instead, it’s developing an eye and seems to also be extending its circulation into the dry air to the north that has been inhibiting its growth:
 

NOAA

NOAA


 
Arthur is still classified as a tropical storm but as of the 2 p.m. Eastern time advisory, they have issued a hurricane watch for Pimlico Sound and Oregon Inlet, North Carolina. They expect the cyclone to turn into a hurricane in 36 hours. As mentioned, I’m not sure if Arthur is following their timetable.

The NHC is also mentioning the possibility that Arthur might possibly track more to the left, i.e., closer to the coast. This indeed is what I see it doing on the current GFS model run, but the ECMWF shows it staying mostly offshore and then curving out to sea like a good little extratropical cyclone.

Models are not destiny. However, if you’re on the East Coast anywhere from Florida to New Brunswick in Canada, do keep a weather eye out.

Here are the current NHC and Canadian Hurricane Centre (CHC) five-day forecast cones. You can see what it might mean if Arthur tracks further to the left:
 


 
Forecast track from the Canadian Hurricane Centre.

Forecast track from the Canadian Hurricane Centre.


 
At its most intense, according to all experts, Arthur is expected to be a high-end Category 1 storm – I would say “only” a Category 1, but I’ve been in one of those and it wasn’t fun. Anyway, that stage is predicted to occur while it’s out to sea, so coastal flooding will probably be the worst threat.
 


 
TS Arthur looks pretty good right now!  (Image:  NOAA)

TS Arthur looks pretty good right now! (Image: NOAA)

July 1, 2014, 1:23 p.m. Pacific: The NHC, at 11 a.m. Central today, identified Tropical Storm Arthur. Right now, they say that it’s getting better organized and are warning interests along the East Coast up to southeastern Virginia to watch this storm carefully. Per Jeff Masters, it appears likely that North Carolina’s Outer Banks are at most risk of a direct hit from a tropical storm/Category 1 hurricane.

From the current NHC forecast discussion:

Northwesterly vertical wind shear is forecast by the models to
gradually subside over the next 48 hours, which should allow the
cyclone to develop its own upper-level outflow pattern. In fact,
latest visible and water vapor imagery indicates that cirrus
outflow has been expanding on the north side of the system during
the past few hours, suggesting that the shear conditions could
already be subsiding. The low shear conditions and warm
sea-surface temperatures should allow for at least steady
strengthening, and the cyclone is expected to become a hurricane by
72 hours. The official intensity forecast is similar to the
latest intensity model consensus IVCN through 36 hours, and then
slightly higher after that.

FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 27.6N 79.3W 35 KT 40 MPH
12H 02/0000Z 27.8N 79.4W 35 KT 40 MPH
24H 02/1200Z 28.7N 79.6W 40 KT 45 MPH
36H 03/0000Z 29.8N 79.5W 50 KT 60 MPH
48H 03/1200Z 31.2N 78.9W 60 KT 70 MPH
72H 04/1200Z 35.4N 75.2W 70 KT 80 MPH
96H 05/1200Z 40.8N 67.3W 65 KT 75 MPH
120H 06/1200Z 45.5N 59.5W 45 KT 50 MPH…POST-TROP/EXTRATROP

Both the ECMWF and GFS models are showing some development of a low pressure system that’s currently meandering around over the warm waters east of St. Augustine, Florida. Something to keep an eye on. The NHC gives it an 80% chance of development over the next five days.
 

Updates will go belowat the top of the page. Be sure to check out the NHC tropical weather outlook and discussion at the link in the photo above. Dr. Jeff Masters at Wunderground also discussed this system, known as Invest 91L at the moment.

As I understand what they’re saying, in the short term, dry air could get drawn into this system’s circulation (which might put a stop to things), and shear will increase some (which at the very least will hinder its development).

However, there is already good spin to the system and it appears to be organizing. It’s forecast to sit over the Gulf Stream all week, which is sort of like keeping a constant supply of fuel going to a balky engine – it may sputter until things start working together, but it will keep running.

Later in the week, shear is forecast to drop some, so this very well could intensify. Its eventual track will be out to sea, but the details of how close to the Atlantic seaboard it will travel, and where, are still anyone’s guess. Stay tuned!


Front page photo credit: Morguefile/MGDboston.



Categories: Weather

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