ATL: GERT - Post-Tropical - Discussion

[cycloneye]

Up to 0%/40%

1. A trough of low pressure located about 650 miles east of the
Leeward Islands continues to produce disorganized showers and
thunderstorms. Environmental conditions are expected to remain
unfavorable for significant development during the next couple of
days. However, environmental conditions are forecast to become
a little more conducive for development late this week while the
system moves generally west-northwestward at about 15 mph over the
western Atlantic.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...40 percent.

[txwatcher91]

Looks like the environment will be improving soon with much lower shear ahead.

[weathaguyry]

I would definitely say that this would be much more of an issue for the OBX northward, as of now Florida will not be affected, and models are not showing it anywhere close to there.

[gatorcane]

The GFS develops an upper-level low just east of the Bahamas in 3 days with increasing wind shear from the north by days 5 and beyond. Plus it shows a lot of dry air as some have pointed out. The situation reminds me of when Hermine was an invest in a similar area last year where the Euro kept showing a hurricane into the Bahamas and South Florida while the GFS did not show much due to upper-level low in Bahamas. GFS ended up verifying as the Euro completely missed the upper-level low.

[weathaguyry]

The GFS develops an upper-level low just east of the Bahamas in 3 days with increasing wind shear from the north by days 5 and beyond. Plus it shows a lot of dry air as some have pointed out. The situation reminds me of when Hermine was an invest in a similar area last year where the Euro kept showing a hurricane into the Bahamas and South Florida while the GFS did not show much due to upper-level low in Bahamas. GFS ended up verifying.

Yes, very similar situation, but just farther east. GFS went on a fathom spree far out, then completely dropped development. Very much like it is doing now with 99L

[blp]

Evolution next 48hours will be very interesting. Some have mentioned that jump to the NNW during the 36-48hr time frame. It shows up in Euro and CMC.

[wxman57]

GFS, EC, and CMC all predict an upper-level & surface pattern along the East U.S. Coast that would support a NE turn offshore. That said, it will come down to timing. If 99L arrives early and/or the upper-trof is a bit late, then there could be a landfall in the Carolinas. For now, my gut says recurve offshore (assuming it develops). I see the NHC is up to 40% beyond 48 hrs. All along, I've said the best chance of this disturbance developing would be farther west, well beyond their 80% at day 5 earlier prediction. I'm thinking 70-80% chance of development Sat/Sun.

[blp]

Problem I see with GFS is it eventually latches onto the northern vorticity once it reaches north of the islands versus the southern one that is stronger and is used by Euro and CMC.

[weathaguyry]

GFS, EC, and CMC all predict an upper-level & surface pattern along the East U.S. Coast that would support a NE turn offshore. That said, it will come down to timing. If 99L arrives early and/or the upper-trof is a bit late, then there could be a landfall in the Carolinas. For now, my gut says recurve offshore (assuming it develops). I see the NHC is up to 40% beyond 48 hrs. All along, I've said the best chance of this disturbance developing would be farther west, well beyond their 80% at day 5 earlier prediction. I'm thinking 70-80% chance of development Sat/Sun.

If 99L gets there early, and the trof is late, could NY/NJ be affected by this, or would it probably only be the Carolinas then out to sea?

[Socalhurcnegirl227]

The GFS develops an upper-level low just east of the Bahamas in 3 days with increasing wind shear from the north by days 5 and beyond. Plus it shows a lot of dry air as some have pointed out. The situation reminds me of when Hermine was an invest in a similar area last year where the Euro kept showing a hurricane into the Bahamas and South Florida while the GFS did not show much due to upper-level low in Bahamas. GFS ended up verifying as the Euro completely missed the upper-level low.

Yup said this yesterday lol very much similar to hermine especially being that hermine was a 99L. Hermine as an invest didnt want to die and apparently neither does possible future Gert.

[cycloneye]

00z Best Track:

AL, 99, 2017080900, , BEST, 0, 160N, 533W, 25, 1011, DB

[AJC3]

The GFS develops an upper-level low just east of the Bahamas in 3 days with increasing wind shear from the north by days 5 and beyond. Plus it shows a lot of dry air as some have pointed out. The situation reminds me of when Hermine was an invest in a similar area last year where the Euro kept showing a hurricane into the Bahamas and South Florida while the GFS did not show much due to upper-level low in Bahamas. GFS ended up verifying as the Euro completely missed the upper-level low.

What I think we may have going on here is a little bit of a chicken vs. egg thing. The GFS and ECM are nearly identical in their 500-200MB height/wind/vort patterns through 00Z SAT. Both models retrograde a pinched off piece of the mid-oceanic trough (i.e. a TUTT low) westward from about 40-45N along 20-25W underneath the mid/upper reflection of the Bermuda ridge for several days.

However, in spite of almost identical mid-upper patterns, there's YUGE difference in the extent of surface development in the two models up through that time. The GFS shows a weak inverted trough with pressures around 1014-1015MB, while the ECM shows a 1007MB TS. Beyond that time, the ECM continues to spin up the TC to where it creates an upper level anticyclone which pretty much eats up whatever is left of the upper low. Any increase in upper tropospheric NE or E shear east of Florida is at least partially attributable to the eastern flank of an upper level (Sonoran) ridge building eastward across the southern U.S.

To me the GFS' lack of development doesn't appear to be due to a stronger upper level low , but rather the lack of development through 72-84 hours results in less development of upper ridging aloft, which allows the upper low to maintain a more coherent identity. Like I said at the beginning of my post...chicken/egg.

[ronjon]

GFS wants to split the vorticity with the northern one becoming dominant. If the southern one developed with its faster motion, it would take it into S FL. Not saying that is likely, but still some uncertainty yet.

[gatorcane]

The GFS develops an upper-level low just east of the Bahamas in 3 days with increasing wind shear from the north by days 5 and beyond. Plus it shows a lot of dry air as some have pointed out. The situation reminds me of when Hermine was an invest in a similar area last year where the Euro kept showing a hurricane into the Bahamas and South Florida while the GFS did not show much due to upper-level low in Bahamas. GFS ended up verifying as the Euro completely missed the upper-level low.

What I think we may have going on here is a little bit of a chicken vs. egg thing. The GFS and ECM are nearly identical in their 500-200MB height/wind/vort patterns through 00Z SAT. Both models retrograde a pinched off piece of the mid-oceanic trough (i.e. a TUTT low) westward from about 40-45N along 20-25W underneath the mid/upper reflection of the Bermuda ridge for several days.

However, in spite of almost identical mid-upper patterns, there's YUGE difference in the extent of surface development in the two models up through that time. The GFS shows a weak inverted trough with pressures around 1014-1015MB, while the ECM shows a 1007MB TS. Beyond that time, the ECM continues to spin up the TC to where it creates an upper level anticyclone which pretty much eats up whatever is left of the upper low. Any increase in upper tropospheric NE or E shear east of Florida is at least partially attributable to the eastern flank of an upper level (Sonoran) ridge building eastward across the southern U.S.

To me the GFS' lack of development doesn't appear to be due to a stronger upper level low , but rather the lack of development through 72-84 hours results in less development of upper ridging aloft, which allows the upper low to maintain a more coherent identity. Like I said at the beginning of my post...chicken/egg.

Thanks for that detailed explanation. That makes sense. Now which model will end up verifying will be interesting as they have such a vastly different outcome for 99l or maybe we will end up with something in the middle of the GFS and ECMWF. By the way, didn't know it was called a Sonoran ridge. Always learning something on Storm2K.

[AJC3]

Thanks for that detailed explanation. That makes sense. Now which model will end up verifying will be interesting as they have such a vastly different outcome for 99l or maybe we will end up with something in the middle of the GFS and ECMWF. By the way, didn't know it was called a Sonoran ridge. Haven't heard that before.

"Sonoran" basically references the area of the US desert SW. It may be a bit of a misnomer to use it in that context, but all it is referencing is essentially a ridge building eastward from the southern tier of the central U.S.

Of course, as much as I hate the GFS-bashfest that often time goes on around here, given that the consensus of the global models and ensembles favor something closer to the ECM solution, I'd have to favor that over the GFS. Plus we're starting to see a pretty good convective blowup right over the center of 99L's primary (southern) vortmax.

[floridasun78]

look like their now storm near area llc tonight let see how look in morning

[AubreyStorm]

Hmmmm! Due west? Interesting for now.

[Digital-TC-Chaser]

EC




The NCEP ens look clear of any low within striking distance atm.

[floridasun78]

Hmmmm! Due west? Interesting for now.

it expect move west untill weekend move to wnw by sat

[weathaguyry]

I really don't think Florida is under the gun with this one, trough is strong and High isn';t quite strong enough to steer it into Florida, that could change, but as of now Florida looks to be pretty safe from this one