ATL: LEE - Models

[RevanTheJedi96]

Lee better weaken considerably if landfall is really its destiny. The areas it is targeting can barely handle CAT 1s.

[LarryWx]

0Z Euro: Very similar to the 0Z GFS, this has a NB landfall 9/17 near 977 mb.

[jconsor]

When examining model guidance for a large, intense hurricane like Lee, it is important to look at more than just 500 mb heights/winds to get a better idea of Lee's future track. Very important to consider the 250 mb level IMHO. There have been a number of cases in which hurricanes were lured NW toward the SE US/Mid-Atlantic coast by a negative tilt trough or cutoff low at 250 mb, even when the 500 mb trough was relatively weak.

When it comes to New England hurricanes, it *usually* takes a deep 500 mb trough from near the Great Lakes to the TN Valley or southern Appalachians (570 dm contour down to at least 40N) to pull a hurricane northward from near/east of the Bahamas toward a New England landfall. Such a deep trough is also necessary to accelerate the hurricane enough (forward speed >25 kt) so it maintains hurricane strength despite the cooler waters N of the Gulf Stream. Look at the upper air patterns for 1938, Carol, Edna, Gloria and Bob and you will see such a deep trough.

On the other hand, the 1893 NYC hurricane and Irene both had much weaker/further north troughs at 500 mb than the hurricanes mentioned above. The 1944 Great Atlantic hurricane had an initially deep trough over the W. Great Lakes/OH Valley two days before landfall, but it was weakening/lifting out as the hurricane turned N up the East Coast. In both the 1893 and 1944 hurricanes, a sharp trough at 250 mb along with a strong jet streak from the NE US to SE Canada helped to compensate for the lack of a deep trough at 500 mb.

Also in Lee's case, a relatively deep/neg tilt 250 mb eastern US trough and 100+ kt jet streak as shown by the GEFS would likely help to compensate.

Also important to note that since the frequency of blocking patterns appears to have increased in the past 30 years since the last New England landfall, and there has been substantial warming of SSTs in those 30 years, history may not be as much of a guide as we would hope. In other words, perhaps in the next few decades we will see increasing frequency of slower-moving strong TSs or lower-end hurricanes (i.e similar to Irene, Sandy and Henri) landfalling in the northern mid-Atlantic and New England vs. what was seen up until ~1990.

[jconsor]

I wrote a detailed thread about the trend in model guidance toward a sharper trough at 250 mb from the eastern Great Lakes to the Carolinas end of this week into this weekend, and how this could increase the risk of Lee continuing N or NNW toward New England instead of turning NNE into Atlantic Canada.

 https://twitter.com/yconsor/status/1700950182156787875




 https://twitter.com/yconsor/status/1700953239267508491




 https://twitter.com/yconsor/status/1700956949838237736




 https://twitter.com/yconsor/status/1700960795960463847




 https://twitter.com/yconsor/status/1701158774151536962

When examining model guidance for a large, intense hurricane like Lee, it is important to look at more than just 500 mb heights/winds to get a better idea of Lee's future track. Very important to consider the 250 mb level IMHO. There have been a number of cases in which hurricanes were lured NW toward the SE US/Mid-Atlantic coast by a negative tilt trough or cutoff low at 250 mb, even when the 500 mb trough was relatively weak.

When it comes to New England hurricanes, it *usually* takes a deep 500 mb trough from near the Great Lakes to the TN Valley or southern Appalachians (570 dm contour down to at least 40N) to pull a hurricane northward from near/east of the Bahamas toward a New England landfall. Such a deep trough is also necessary to accelerate the hurricane enough (forward speed >25 kt) so it maintains hurricane strength despite the cooler waters N of the Gulf Stream. Look at the upper air patterns for 1938, Carol, Edna, Gloria and Bob and you will see such a deep trough.

On the other hand, the 1893 NYC hurricane and Irene both had much weaker/further north troughs at 500 mb than the hurricanes mentioned above. The 1944 Great Atlantic hurricane had an initially deep trough over the W. Great Lakes/OH Valley two days before landfall, but it was weakening/lifting out as the hurricane turned N up the East Coast. In both the 1893 and 1944 hurricanes, a sharp trough at 250 mb along with a strong jet streak from the NE US to SE Canada helped to compensate for the lack of a deep trough at 500 mb.

Also in Lee's case, a relatively deep/neg tilt 250 mb eastern US trough and 100+ kt jet streak as shown by the GEFS would likely help to compensate.

Also important to note that since the frequency of blocking patterns appears to have increased in the past 30 years since the last New England landfall, and there has been substantial warming of SSTs in those 30 years, history may not be as much of a guide as we would hope. In other words, perhaps in the next few decades we will see increasing frequency of slower-moving strong TSs or lower-end hurricanes (i.e similar to Irene, Sandy and Henri) landfalling in the northern mid-Atlantic and New England vs. what was seen up until ~1990.

[hohnywx]

0Z Euro: Very similar to the 0Z GFS, this has a NB landfall 9/17 near 977 mb.

More importantly, it has shifted back west to provide significant impacts to New England

[Kazmit]

Starting to see a bit of a W bend toward New England…

[pgoss11]

Starting to see a bit of a W bend toward New England…

https://i.ibb.co/ys4vb7B/13-L-tracks-latest.png

But to me it looks like most of them turn toward away from the US

[hohnywx]

Starting to see a bit of a W bend toward New England…

https://i.ibb.co/ys4vb7B/13-L-tracks-latest.png

But to me it looks like most of them turn toward away from the US

Lee is passing close enough that the impacts will be felt regardless. The wind field is going to be quite large by the time it reaches this latitude. For example, the Canadian is well offshore but still brings TS-force gusts to Massachusetts and Maine (almost hurricane-force to Cape Cod).

[Dsci4]

Starting to see a bit of a W bend toward New England…

https://i.ibb.co/ys4vb7B/13-L-tracks-latest.png

Of note here is that these runs no longer seem to show that more westerly bend before the turn north. I believe that has changed as it def had more of a left bend before the right bend look

[wxman57]

Once Lee reaches the latitude of Cape Cod, it will be in the process of becoming ET. It's wind field will double in size, with TS winds raking the coast of Maine down to as far west as eastern Long Island. Max winds may only be 50-60 kts by then and 50 kts at final landfall. Even though the pressure will be quite low, the expansion of the wind field will reduce the pressure gradient and max sustained winds will drop. TS wind may extend out to 250 miles west of its center as it passes Cape Cod.

[wxman57]

By the way, the new consensus (TVCN) takes the center just west of Nova Scotia an into New Brunswick next Sunday. That's right along our track. Probably 50-55 kts at landfall up there but with a huge area of TS winds as it transitions to ET.

[ColdMiser123]

Since there is still some uncertainty left in the exact track evolution, there's also uncertainty in exactly how strong this is at landfall as well.

You can see three camps on the latest 6z EPS. One cluster that takes this over Boston, one that would pass very close to, or over Maine, and one that takes this over Nova Scotia.

If this takes the leftward cluster's track, there would be less time for weakening over colder water to take place before making landfall. More weakening the longer it stays over the Gulf of Maine.

[dspguy]

Starting to see a bit of a W bend toward New England…

https://i.ibb.co/ys4vb7B/13-L-tracks-latest.png

But to me it looks like most of them turn toward away from the US

"All models are wrong, but some are useful."

Look back at Irma in 2017. Nearly all models as far out as we are with Lee were showing a coast scraper from FL to the Carolinas. Only one showed it going on the Gulf side of Florida at 3 days out. And that was the "most right" model. When the models show such consensus like we have now with Lee, many feel confident that the "solution" is already known when in reality it very well could move further west into New England or further east and miss a landfall in Nova Scotia.

[Xyls]

Starting to see a bit of a W bend toward New England…

https://i.ibb.co/ys4vb7B/13-L-tracks-latest.png

This riding up the Bay of Fundy or just to the north of would be a worst case scenario for Lee, this would drive huge storm surges up into the Bay and could be an 1869 Saxby Gale kind of scenario. Let's hope this does not happen.

I'm still thinking most likely landfall will be Washington Co, ME or Charlotte Co, NB.

[cheezyWXguy]

This is why when Lee was first getting going, it was important to hammer home the notion of uncertainty.

All things considered, from a track perspective at least, the models actually have done a pretty impressive job of seeing the general track well in advance. However, in cases like this, or Ian for that matter, where the storm is moving generally parallel to a populated coastline, a relatively small deviation to the left or right can produce significantly different impacts.

NHC forecast cones don’t go beyond 5 days for a reason, and we posters obviously don’t have any special information that they don’t when we speculate. Don’t get me wrong, I say speculate away. A lot of us are here to do just that and test our ability to make an amateur forecast. But we need to acknowledge it for what it is and is not. Point being, let’s try and do without the declarative posts on “fish” or specifc landfall locations 10 days out for the next one.

[Hybridstorm_November2001]

Starting to see a bit of a W bend toward New England…

https://i.ibb.co/ys4vb7B/13-L-tracks-latest.png

But to me it looks like most of them turn toward away from the US

"All models are wrong, but some are useful."

Look back at Irma in 2017. Nearly all models as far out as we are with Lee were showing a coast scraper from FL to the Carolinas. Only one showed it going on the Gulf side of Florida at 3 days out. And that was the "most right" model. When the models show such consensus like we have now with Lee, many feel confident that the "solution" is already known when in reality it very well could move further west into New England or further east and miss a landfall in Nova Scotia.

A good word of advice indeed.

"The trend is your friend". Lee's model trend is more westward with time. Let us see if that holds in the days to come.

Edit - At this point a Cape Cod landfall or very close pass would not shock me at all.

[Hybridstorm_November2001]

Just spitballing here but I could see an landfall track similar to the Saxy Gale of October 1869 eventually unfolding given current trends -



https://en.wikipedia.org/wiki/1869_Saxby_Gale

[LarryWx]

For the record 6Z GFS landfalls on E ME 9/17

[LarryWx]

Trying to keep this going as long as countable to follow trend and for record:

EPS 0Z/12Z US landfalls: two 20%+ in a row

9/11 0Z: ~12 (24%): ~9 ME, 1 MA, 1 RI, 1 NY

9/10 12Z: 10 (20%): 6 ME, 3 MA, 1 RI

9/10 0Z: 3 (6%): 1 ME, 2 MA

9/9 12Z: 6 (12%) 9/17-19 (3 ME, 3 MA)
9/9 0Z: 3 (6%) 9/17 (3 ME)
9/8 12Z: 5 (10%) 9/15-18 (5 ME)
9/8 0Z: 7 (14%) 9/15-17 (6 ME, 1 NY)
9/7 12Z: 12 (24%) 9/15-19 (7 ME, 3 MA, 1 NY, 1 NJ)
9/7 0Z: 10 (20%) 9/15-18 (5 ME, 5 MA)
9/6 12Z: 3 (6%) 9/15-18 (2 ME, 1 MA)
9/6 0Z: 5 (10%)
9/5 12Z: 2 (4%)
9/5 0Z: 4 (8%)
9/4 12Z: 1 (2%)
9/4 0Z: 2 (4%)

[LarryWx]

For record/trend following purposes, GEFS US landfalls: last 4 runs 26-42% US landfalls

6Z GEFS: ~10 (32%) ~6 ME, 2 MA, 2 RI

Last 12 GEFS runs: 32%, 29%, 26%, 42%, 10%, 13%, 26%, 16%, 16%, 10%, 10%, 10%