ATL: FAY - Post-Tropical - Discussion

[Steve]

https://www.ospo.noaa.gov/data/sst/contour/natlanti.fc.gif

Water temps are looking nice and toasty once the circulation gets offshore. 24C waters extend all the way to NYC and southern Long Island, so there’s no cold water to weaken this rapidly as it approaches the Northeast. I’m already starting to prepare for some nasty high tide cycles in the bays on Long Island on Friday/Saturday.

I’m mainly concerned about the large pool of 28-29 C SSTs in the Gulf Stream. 98L will emerge over it no matter what, and could sit on top of it for up to 48 hours. We could see it quickly spin up, and perhaps intensify more than the models have been showing, but that really depends on the size and structure of its circulation once it is full over water.

They are warm but only about up to 37N though - unless it was to be right along the NJ shoreline as it was coming north toward Long Island/CT/RI/MA. Models are still disagreeing about how far off the coast 98L will even get, and that's the ones that take it to water. It could conceivably get out to water and come back up through NC which would further disrupt the structure. ICON and HRRR have been leaders in wanting it to be in the water. Latest run of the ICON (out to 75 hours) shows probably the eastern outlier track. It's got the circulation rounding the outside of the OBX and still moving NNE as it heads toward Long Island

wait - it just kicked in to 108 hours. So it goes to Long Island and then cuts NE/ENE, crosses over Cape Cod and ends up nosing along the Maine border up toward its border with New Brunswick. It peaks it around 999/998mb.

[Steve]

Rather quiet thread for an east coast threat

I'd say things will pick up a little if it gets named. But like Cristobal, it was only ever likely to be a midgrade storm which doesn't bring out as many people. Under extreme threats, they'll sometimes be a couple hundred lurkers.

[Aric Dunn]

the main circ has reformed/started movie ese pretty quickly about 50 miles or so.. the process has begun.

will be an interesting next several hours.

luckily it is very near a radar site and we have a lot of surface obs.

satellite is slightly lagging behind what is happening at the surface.

[CyclonicFury]

The exact location of where an LLC forms, and its size, will be important. Most of the global models, aside from the ICON and UKMET, have kept 98L weak, elongated and very close to the U.S. East Coast. SSTs off the coast of the Carolinas are very warm, though models are not in agreement of whether 98L will spend enough time over these waters to strengthen significantly.

I'd say there is a sizable chance that 98L could make landfall in New England, likely as a tropical storm.

So far the UKMET has been right in line with the short HRRR motion and reformation..

What is the UKMET forecasting for maximum intensity and landfall?

Posted it in the models thread, peaks at 989 mb.

[Steve]

Well, it seems to me like it's probably going to develop once it gets off the coast from what I'm reading here. On the other hand, some of the models and the NHC are less bullish, so I'm just kind of seeing how it plays out. People seem pretty confident that it will head to New England, what are the reasons for that? Could it take another path if it does develop, especially considering the uncertainties about where the center will reform and all that?

There really isn't anywhere for it to go except basically north. Run the model in the link below, and you'll see why. This is the 500mb run of the GFS which is the air pressure at just over 3 1/2 miles. The darker the red, the higher the pressure. What happens is about the entire Atlantic Ocean is under a giant high right now. That blocks any moves to the East or ENE because the flow around it on that side is up from the south and it's not going to penetrate through the high. So it moves north and eventually around NY State (on the GFS) a shortwave trough is coming from its west which will pick it up. That's the pale colored "v" shape in Ohio and Pennsylvania at 90 hours. At that point, it will pull up and out and will have to go NNE or NE because the flow in front of a shortwave is always out of the Southwest*. But other than hooking into land somewhere farther south, that's the way the energy is going. It's going to end up in the Canadian Maritimes and probably be absorbed soon afterwards.

https://www.tropicaltidbits.com/analysi ... 70712&fh=6

* flow around high pressure is clockwise; flow around low pressure is counter-clockwise

[Do_For_Love]

Thanks for sharing that info & site! Very interesting

[Steve]

Thanks for sharing that info & site! Very interesting

No problem. That site is hosted by Levi Cowan and updates as the models come in. It gets swamped during big threats sometimes. He'll usually put out nightly videos that gets posted on Storm2k when there are specific threats. He is a member here. Dylan Federico also puts out some dynamite videos when there are threats as well. Both of those guys are worth following if/whenever there are tropical threats.

[Ubuntwo]

Well, it seems to me like it's probably going to develop once it gets off the coast from what I'm reading here. On the other hand, some of the models and the NHC are less bullish, so I'm just kind of seeing how it plays out. People seem pretty confident that it will head to New England, what are the reasons for that? Could it take another path if it does develop, especially considering the uncertainties about where the center will reform and all that?

There really isn't anywhere for it to go except basically north. Run the model in the link below, and you'll see why. This is the 500mb run of the GFS which is the air pressure at just over 3 1/2 miles. The darker the red, the higher the pressure. What happens is about the entire Atlantic Ocean is under a giant high right now. That blocks any moves to the East or ENE because the flow around it on that side is up from the south and it's not going to penetrate through the high. So it moves north and eventually around NY State (on the GFS) a shortwave trough is coming from its west which will pick it up. That's the pale colored "v" shape in Ohio and Pennsylvania at 90 hours. At that point, it will pull up and out and will have to go NNE or NE because the flow in front of a shortwave is always out of the Southwest*. But other than hooking into land somewhere farther south, that's the way the energy is going. It's going to end up in the Canadian Maritimes and probably be absorbed soon afterwards.

https://www.tropicaltidbits.com/analysi ... 70712&fh=6

* flow around high pressure is clockwise; flow around low pressure is counter-clockwise

Just a technicality, but the visualization you have on that run is geopotential height, not MSLP. So darker red = higher altitude 500mb zone. A higher geopotential height is generally correlated with higher pressure but it's not 1:1 (latitude plays a big part).

[aspen]

Nearly all of 98L’s convection has moved offshore. With the original center still on land and so much convection over the Gulf Stream, it looks like a center reformation is inevitable.

[Aric Dunn]

Nearly all of 98L’s convection has moved offshore. With the original center still on land and so much convection over the Gulf Stream, it looks like a center reformation is inevitable.

it is highly probable.

once the sun sets and we start to lose the effects of daytime heating convection should build along and just offshore and that is when we will likely see it happen.

[CyclonicFury]

A new center forming offshore much sooner than forecast would change things significantly.

So far, most of the dynamical models have been insistent that 98L will remain a broad mess with no single well-defined center for the next 36-48 hours or so, with a center possibly developing near the Outer Banks of North Carolina around that time. That is likely why the global models, aside from the UKMET and ICON, only show a weak, broad tropical storm.

[Steve]

Well, it seems to me like it's probably going to develop once it gets off the coast from what I'm reading here. On the other hand, some of the models and the NHC are less bullish, so I'm just kind of seeing how it plays out. People seem pretty confident that it will head to New England, what are the reasons for that? Could it take another path if it does develop, especially considering the uncertainties about where the center will reform and all that?

There really isn't anywhere for it to go except basically north. Run the model in the link below, and you'll see why. This is the 500mb run of the GFS which is the air pressure at just over 3 1/2 miles. The darker the red, the higher the pressure. What happens is about the entire Atlantic Ocean is under a giant high right now. That blocks any moves to the East or ENE because the flow around it on that side is up from the south and it's not going to penetrate through the high. So it moves north and eventually around NY State (on the GFS) a shortwave trough is coming from its west which will pick it up. That's the pale colored "v" shape in Ohio and Pennsylvania at 90 hours. At that point, it will pull up and out and will have to go NNE or NE because the flow in front of a shortwave is always out of the Southwest*. But other than hooking into land somewhere farther south, that's the way the energy is going. It's going to end up in the Canadian Maritimes and probably be absorbed soon afterwards.

https://www.tropicaltidbits.com/analysi ... 70712&fh=6

* flow around high pressure is clockwise; flow around low pressure is counter-clockwise

Just a technicality, but the visualization you have on that run is geopotential height, not MSLP. So darker red = higher altitude 500mb zone. A higher geopotential height is generally correlated with higher pressure but it's not 1:1 (latitude plays a big part).

That's right. I used geopotential heights because I felt like it would best explain the question do_for_love asked as to what was most likely. 500 heights with MSLP would have been a close depiction in this case I'm sure.

Caveat is that I don't particularly buy the GFS's take on 98L, but I think it has the upper pattern pretty close.

[cycloneye]

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Tue Jul 7 2020

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

An area of low pressure located inland along the Georgia-South
Carolina border southeast of Augusta, Georgia, continues to produce
a large area of showers and heavy rain over portions of the
southeastern United States. The low is expected to move slowly
eastward overnight before turning east-northeastward on Wednesday.
By Wednesday night and Thursday, the system is forecast to move
generally northeastward near or just offshore the coast of the
Carolinas and the mid-Atlantic states, and a tropical or
subtropical cyclone could form later this week if the low moves
over the warm waters of the western Atlantic. Regardless of
development, the low is expected to produce locally heavy rainfall
that could cause flash flooding across portions of the southeastern
U.S. during the next couple of days.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...medium...50 percent.

$$
Forecaster Stewart

[cycloneye]

98L INVEST 200708 0000 33.3N 82.0W ATL 20 1014

[Aric Dunn]

winds at the coast from savannah to Charleston are starting to diverge.. switching to sw and wsw they should still be ese to SE the circ inland is weakening quickly.. and a thin line of convection is developing right along the coast as expected.

lets see if it expands and slides farther offshore.

[Aric Dunn]

wish I could stay up and see how this progresses.. but I have do that whole work thing in the morning.. ugh..

[hipshot]

wish I could stay up and see how this progresses.. but I have do that whole work thing in the morning.. ugh..

Are you working from home?

[Steve]

Not too much is happening right now. I think it's a transition period. There's a lot of flow out of the west, and as Aric has been saying, look for more and more storms to start popping in the coastal waters over the next few hours. I'm probably going to bed early, but a circulation could pop over water tonight and consolidate throughout the day tomorrow near the NC Coast. NAM (all resolutions) keep it pretty weak, though they do depict at least a tropical depression. 3km has it at the Delmarva Peninsula at 60 hours (Friday am) and keeps it mostly hugging the coast on the way up. 12km and 32km resolutions keep it broad and weak. NAM is more or less indicating a party storm.

[Aric Dunn]

wish I could stay up and see how this progresses.. but I have do that whole work thing in the morning.. ugh..

Are you working from home?

For the time being yeah..

[NXStumpy_Robothing]

Not too much is happening right now. I think it's a transition period. There's a lot of flow out of the west, and as Aric has been saying, look for more and more storms to start popping in the coastal waters over the next few hours. I'm probably going to bed early, but a circulation could pop over water tonight and consolidate throughout the day tomorrow near the NC Coast. NAM (all resolutions) keep it pretty weak, though they do depict at least a tropical depression. 3km has it at the Delmarva Peninsula at 60 hours (Friday am) and keeps it mostly hugging the coast on the way up. 12km and 32km resolutions keep it broad and weak. NAM is more or less indicating a party storm.

I don't think the original center migrating towards the new convection can be ruled out either. It's currently crossing the GA/SC border south of Augusta with an ESE direction, and shear is still mostly unfavorable for something to easily spin up off the coast.