ATL: GERT - Post-Tropical - Discussion

[cycloneye]

BULLETIN
Tropical Storm Gert Advisory Number 8
NWS National Hurricane Center Miami FL AL082017
500 PM EDT Mon Aug 14 2017

...GERT CONTINUES TO STRENGTHEN...
...EXPECTED TO BECOME A HURRICANE TONIGHT...


SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...30.6N 72.3W
ABOUT 455 MI...735 KM WSW OF BERMUDA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...N OR 360 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...992 MB...29.30 INCHES

Tropical Storm Gert Discussion Number 8
NWS National Hurricane Center Miami FL AL082017
500 PM EDT Mon Aug 14 2017

The satellite presentation of Gert has continued to improve today.
Convective banding has increased around the center, and a large
banded eye has appeared in recent visible satellite pictures.
Satellite intensity estimates from TAFB, SAB, and UW-CIMSS supported
an intensity of around 55 kt at 18z, but due to the continued
increase in organization, the initial wind speed is set at 60 kt
for this advisory. Although there is some light northerly shear
over the system, it should not prevent additional strengthening
during the next day or so while Gert remains over SSTs of 28 to
29 deg C. Gert is expected to become a hurricane within 12 hours,
and the updated NHC intensity forecast calls for a bit higher peak
intensity than before. The NHC forecast is a little above the
statistical guidance and calls for peak intensity a little sooner
than most of the guidance. The HWRF continues to be very bullish
in bringing the system to major hurricane status, but since it
shows peak intensity well after the system is expected to encounter
westerly shear and cooler SSTs, less weight has been placed on that
scenario. Gert is expected to complete extratropical transition
within 72 hours, then gradually weaken over the North Atlantic
before it merges with a larger extratropical cyclone in 4 to 5 days.

Gert has been moving more slowly than expected today while it has
been rounding the western portion of the ridge. The storm is
expected to turn north-northeastward and begin to accelerate
Tuesday ahead of a shortwave trough approaching the northeastern
United States. The track guidance continues to be in excellent
agreement, but is generally slower than before. As a result, little
cross-track change was required in the NHC track through 72 h, but
the new forecast is slower than the previous one to account for the
latest trend in the latest guidance.

Swells from Gert are expected to spread northward along the
mid-Atlantic coast of the United States during the next few days.
These swells are likely to produce dangerous surf and rip current
conditions. Please consult products from your local National
Weather Service office.

FORECAST POSITIONS AND MAX WINDS

INIT 14/2100Z 30.6N 72.3W 60 KT 70 MPH
12H 15/0600Z 31.6N 72.3W 70 KT 80 MPH
24H 15/1800Z 33.3N 71.6W 75 KT 85 MPH
36H 16/0600Z 35.6N 69.0W 80 KT 90 MPH
48H 16/1800Z 38.0N 64.0W 80 KT 90 MPH
72H 17/1800Z 44.5N 48.0W 70 KT 80 MPH...POST-TROP/EXTRATROP
96H 18/1800Z 52.0N 39.0W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 19/1800Z...ABSORBED BY LARGER EXTRATROPICAL LOW

$$
Forecaster Brown

[OuterBanker]

I'm gonna keep a close eye on this. It will not hit the US mainland, but until it makes its turn and at least passes 35 N. I would prefer that it would turn earlier. The longer it hangs the more beach erosion it will cause.
Waiting for the surfers to show up. Prefer them to the news media.

[Emmett_Brown]

Since Gert has slowed a bit, and will have a little more time over hot water, it's fun to contemplate that ex 99L could be the first major 'cane of the season, just a few days after many were calling on bones to declare it dead. Quite an amazing come back. It just shows how tropical waves don't just disappear, no matter how homely they look, they can and often will develop once conditions allow.

[GCANE]

Two large overshooting towers firing on the SE quad eyewall

[Hurricaneman]

The 18zGFS has nearly a major in 24 hrs and one thing I can say is that is not completely unreasonable

[xironman]

I'm gonna keep a close eye on this. It will not hit the US mainland, but until it makes its turn and at least passes 35 N. I would prefer that it would turn earlier. The longer it hangs the more beach erosion it will cause.
Waiting for the surfers to show up. Prefer them to the news media.

The surfers at the S-Turns in Rodanthe are going to have field day.

[Kingarabian]

Looks really close to a hurricane if not one already.

However, dry air is still entrained in the core so it'll need to mix that out ASAP in order for it to RI into something stronger before it reaches unfavorable conditions.

[Hammy]

Good bet that eye feature isn't there now, the cloud temps have really warmed significantly in just the few hours since the advisory came out.

[Kingarabian]

:uarrow: Good bet that eye feature isn't there now, the cloud temps have really warmed significantly in just the few hours since the advisory came out.

Yeah, let's see if it can fire off some hot towers soon and improve its inner structure and allow it to become a hurricane by the next advisory.

[Hammy]

Is Gert strong enough for upwelling? It certainly hasn't been moving much.

[CrazyC83]

TXNT21 KNES 150004
TCSNTL

A. 08L (GERT)

B. 14/2345Z

C. 30.6N

D. 72.6W

E. ONE/GOES-E

F. T4.5/4.5/D2.0/24HRS

G. IR/EIR/SWIR

H. REMARKS...OW EYE EMBEDDED AND SURROUNDED BY DG YIELDS A DT OF 4.5. NO
EYE ADJUSTMENTS MADE. MET=4.0 AND PT=4.5. FT IS BASED ON DT.

I. ADDL POSITIONS

NIL


...KIM

[Hammy]

I think it's safe to say RI is out of the question at this point, given the dry air present.

[TheStormExpert]

 https://twitter.com/richjohnsonwx/status/897252333301760002

[SouthDadeFish]

I think it's safe to say RI is out of the question at this point, given the dry air present.

If the intensity is 70 kt at the 11 pm advisory then the 30 kt in 24 h RI criterion will have been satisfied. Given the T 4.5 estimate, that is quite possible.

[SouthDadeFish]

 https://twitter.com/richjohnsonwx/status/897252333301760002

I disagree. Microwave imagery clearly shows an eye present. The eyewall is broken to the NW though.

[cycloneye]

Hurricane at 11 PM.

AL, 08, 2017081500, , BEST, 0, 308N, 723W, 65, 986, HU

[MississippiWx]

Definitely an eye.

[Kingarabian]

I think it's safe to say RI is out of the question at this point, given the dry air present.

If the intensity is 70 kt at the 11 pm advisory then the 30 kt in 24 h RI criterion will have been satisfied. Given the T 4.5 estimate, that is quite possible.

i think that the T 4.5 will not reflect Gert's correct intensity considering how shallow and warm the convection currently is.

[SouthDadeFish]

I think it's safe to say RI is out of the question at this point, given the dry air present.

If the intensity is 70 kt at the 11 pm advisory then the 30 kt in 24 h RI criterion will have been satisfied. Given the T 4.5 estimate, that is quite possible.

i think that the T 4.5 will not reflect Gert's correct intensity considering how shallow and warm the convection currently is.

I don't disagree. My point was to say that RI has already nearly been satisfied. I wouldn't say it's "out of the question." Perhaps Hammy was referring to future RI though. Regardless, Gert goes to show how challenging it is to accurately forecast TC intensity in moderate vertical wind shear.

[Hammy]

If the intensity is 70 kt at the 11 pm advisory then the 30 kt in 24 h RI criterion will have been satisfied. Given the T 4.5 estimate, that is quite possible.

i think that the T 4.5 will not reflect Gert's correct intensity considering how shallow and warm the convection currently is.

I don't disagree. My point was to say that RI has already nearly been satisfied. I wouldn't say it's "out of the question." Perhaps Hammy was referring to future RI though. Regardless, Gert goes to show how challenging it is to accurately forecast TC intensity in moderate vertical wind shear.

Yes, I meant future RI. I don't think Gert will reach more than 65-70kt at this point if the surrounding air remains as dry as it is, and I do wonder if there is some upwelling going on as well given the slow speed.

edit: apparently intensification is still underway as Tropical Atlantic lists Gert as a hurricane now. Did a quick check, and it looks like 2004 was the last time we had two hurricanes in the first half of August.