ATL: TAMMY - Post-Tropical - Discussion

[aspen]

Lol look at the location of the 'eye' according to the automated ADT site. No wonder you only get a raw T# of 4.0 that way

https://i.imgur.com/pMRsBJK.gif

ADT really needs an update. It’s been so bad with eye placements this season, and this shows it’s not just with pinholes.

[kevin]

Visible imagery is continuing to improve and the eye has now fully cleared out, look at the difference between now and 1 hour ago. This is a cat 3.

[zzzh]

NHC has been underestimating this since 00z. This is at least a MH.

[kevin]

NHC went with 90 kt for 11am. Maybe they're seeing something I'm not, but imo it's clearly a MH. Anyways, they're the experts and if they underestimated it they'll probably correct it in their post-season analysis.

000
WTNT45 KNHC 251454
TCDAT5

Hurricane Tammy Discussion Number 29
NWS National Hurricane Center Miami FL AL202023
1100 AM AST Wed Oct 25 2023

Tammy has improved its satellite presentation this morning. Since
the previous advisory, the hurricane briefly had a symmetric eye in
the satellite infrared and microwave imagery. A nearby deep-layer
trough appears to be limiting the western portion of Tammy's
outflow. The subjective and objective intensity estimates have
increased to 89 to 92 kt, and therefore the initial intensity has
been raised to 90 kt.

The upper-level environmental conditions are expected to be
conducive for the next few hours with enhanced 200 mb divergence
associated with the aforementioned trough. After 12 hours, the
divergence is expected to decrease and strong shear, cooling SSTs,
and surrounding dry subsident air should gradually weaken the
hurricane. Model guidance suggests Tammy will undergo extratropical
transition by Thursday and as a result, the tropical-storm-force
wind field is expected to expand. The official intensity forecast is
similar to the previous advisory and follows the various consensus
aids.

Tammy is moving northeastward at about 11 kt, within the flow
between a deep-layer trough over the western Atlantic and a
subtropical ridge over the central Atlantic. Later today, the
cyclone is expected to turn northward followed by a
north-northwestward to northwestward turn on Thursday with a slower
forward speed. By Friday, Tammy is expected to meander over the
northwestern Atlantic in the light steering currents between two
building ridges over the eastern Atlantic and southeastern United
States. The 3- to 5-day steering flow forecast is rather uncertain
and as a result there is a large spread in the track model guidance
after 48 hours. The latest NHC track forecast is east of the
previous prediction and favors the left side of the guidance
envelope.



FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 26.6N 59.3W 90 KT 105 MPH
12H 26/0000Z 28.2N 58.8W 85 KT 100 MPH
24H 26/1200Z 29.8N 59.5W 75 KT 85 MPH...POST-TROP/EXTRATROP
36H 27/0000Z 30.5N 60.7W 65 KT 75 MPH...POST-TROP/EXTRATROP
48H 27/1200Z 31.0N 61.8W 60 KT 70 MPH...POST-TROP/EXTRATROP
60H 28/0000Z 31.2N 62.2W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 28/1200Z 31.4N 62.7W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 29/1200Z 31.7N 63.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 30/1200Z 31.9N 63.0W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci/R. Zelinsky

[cycloneye]

Another record for the 2023 season. (Tied)

 https://twitter.com/philklotzbach/status/1717189799864381791

[ScottNAtlanta]

They (NHC) really seem a little fast in wanting to declare this "post-tropical" in their forecast.

[ElectricStorm]

Yeah I agree this is probably a major. If they don't upgrade operationally hopefully they will in the TCR

[aspen]

NHC went with 90 kt for 11am. Maybe they're seeing something I'm not, but imo it's clearly a MH. Anyways, they're the experts and if they underestimated it they'll probably correct it in their post-season analysis.

000
WTNT45 KNHC 251454
TCDAT5

Hurricane Tammy Discussion Number 29
NWS National Hurricane Center Miami FL AL202023
1100 AM AST Wed Oct 25 2023

Tammy has improved its satellite presentation this morning. Since
the previous advisory, the hurricane briefly had a symmetric eye in
the satellite infrared and microwave imagery. A nearby deep-layer
trough appears to be limiting the western portion of Tammy's
outflow. The subjective and objective intensity estimates have
increased to 89 to 92 kt, and therefore the initial intensity has
been raised to 90 kt.

The upper-level environmental conditions are expected to be
conducive for the next few hours with enhanced 200 mb divergence
associated with the aforementioned trough. After 12 hours, the
divergence is expected to decrease and strong shear, cooling SSTs,
and surrounding dry subsident air should gradually weaken the
hurricane. Model guidance suggests Tammy will undergo extratropical
transition by Thursday and as a result, the tropical-storm-force
wind field is expected to expand. The official intensity forecast is
similar to the previous advisory and follows the various consensus
aids.

Tammy is moving northeastward at about 11 kt, within the flow
between a deep-layer trough over the western Atlantic and a
subtropical ridge over the central Atlantic. Later today, the
cyclone is expected to turn northward followed by a
north-northwestward to northwestward turn on Thursday with a slower
forward speed. By Friday, Tammy is expected to meander over the
northwestern Atlantic in the light steering currents between two
building ridges over the eastern Atlantic and southeastern United
States. The 3- to 5-day steering flow forecast is rather uncertain
and as a result there is a large spread in the track model guidance
after 48 hours. The latest NHC track forecast is east of the
previous prediction and favors the left side of the guidance
envelope.



FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 26.6N 59.3W 90 KT 105 MPH
12H 26/0000Z 28.2N 58.8W 85 KT 100 MPH
24H 26/1200Z 29.8N 59.5W 75 KT 85 MPH...POST-TROP/EXTRATROP
36H 27/0000Z 30.5N 60.7W 65 KT 75 MPH...POST-TROP/EXTRATROP
48H 27/1200Z 31.0N 61.8W 60 KT 70 MPH...POST-TROP/EXTRATROP
60H 28/0000Z 31.2N 62.2W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 28/1200Z 31.4N 62.7W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 29/1200Z 31.7N 63.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 30/1200Z 31.9N 63.0W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci/R. Zelinsky

If that 127 kt SAR pass is legit, then they’re severely underestimating this. I think ADT/SATCON’s low bias is dragging this down. Hopefully it maintains a strong satellite presentation and gets upgraded at 5pm.

[MarioProtVI]

That SAR pass makes a solid case for 100 kt. If it manages to hold onto its current presentation until 18z-21z I can see them upgrading it but I’m not confident as the N side is beginning to degrade. They might go 95 kt instead and probably mention the SAR pass with a note of perhaps how they’ll revisit it in analysis.

[Teban54]

Welp, looks like Tammy is on a weakening trend now. CDO thinning to the north, and the eye has become more squished in the last hour.

[cycloneye]

Is making the transition to extratropical.

 https://twitter.com/OSUWXGUY/status/1717223255604363648

[aspen]

Dropped to 85 kt in the 18z BT. This is a rare instance of something that’s highly likely to be a major just never getting upgraded. Alvin was another one. ADT did a bad job with both systems, because I guess it needs an eye 50 miles wide to be correct.

[Vince_and_Grace_fan]

Nice satellite presentation of the long frontal cloudiness extending from Tammy toward SW-Europe at 12Z (EUMETSAT).

[CrazyC83]

That was definitely T5.5, if not T6.0 there. 105 kt would be my guess earlier as a peak at 1200Z (90 kt now).

[Sciencerocks]

[Sciencerocks]

[Dean_175]

Within the past few hours (in the time since the photos from the user ScienceRocks above were added) , Tammy looks like it is now well underway unwrapping into a post-tropical cyclone. Most of the moisture fueling the convection has been pushed upward above the cooler air across the frontal boundary, has the distinct comma shape, and doesn't look very tropical at all anymore. Minimum cloud top temperatures have risen several tens of degrees C(35C+ where the convective center was) as convection dissipates(. It appears like its convective core has completely disintegrated. That said, strong winds persist regardless of classification. Bermuda could still receive tropical storm winds late tomorrow night or Friday. On satellite, it just looks like a typical maritime extratropical cyclone sucking humid air directly from the tropics. Does anyone think it could wrap itself back up again once it is pushed westward?

[cycloneye]

They say it could be tropical again.

Though it is
not explicitly forecast, there is some potential based on the GFS
and ECMWF simulated satellite imagery that Tammy could reacquire
tropical characteristics this weekend or early next week. The
chances of the system transitioning back to a tropical cyclone will
be evaluated in routine Tropical Weather Outlooks.

[WalterWhite]

Dropped to 85 kt in the 18z BT. This is a rare instance of something that’s highly likely to be a major just never getting upgraded. Alvin was another one. ADT did a bad job with both systems, because I guess it needs an eye 50 miles wide to be correct.

This could get upgraded in post-season analysis, but it is very rare for the NHC to change the peak intensity of a storm by more than 5 knots.

[cycloneye]

They are mentioning it in TWO.

Northwestern Atlantic (Post-Tropical Cyclone Tammy):
A strong extratropical cyclone (former Tammy) associated with a
stationary front is located a few hundred miles east-southeast of
Bermuda. There is a possibility this system could regain tropical
or subtropical characteristics while it meanders over the
northwestern Atlantic through early next week. Regardless of
development, the system has the potential to bring gusty winds and
heavy rainfall to Bermuda. Interests in the area should monitor the
progress of this system. For additional information, including gale
warnings, see the High Seas Forecasts issued by the National Weather
Service and products from the Bermuda Weather Service.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 7 days...low...30 percent.