ATL: TAMMY - Advisories

[cycloneye]

BULLETIN
Hurricane Tammy Advisory Number 15
NWS National Hurricane Center Miami FL AL202023
1100 PM AST Sat Oct 21 2023

...TAMMY JUST NORTH-NORTHWEST OF BARBUDA...
...CONTINUES TO BRING STRONG WINDS AND HEAVY RAINS OVER
PORTIONS OF THE LEEWARD ISLANDS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.8N 61.9W
ABOUT 15 MI...25 KM NNW OF BARBUDA
ABOUT 80 MI...130 KM ESE OF ST. MARTIN
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...NNW OR 330 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...992 MB...29.30 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

The government of Antigua and Barbuda has discontinued the
Hurricane Warning for Antigua, and discontinued the Tropical Storm
Watch for the British Virgin Islands.

Hurricane Tammy Discussion Number 15
NWS National Hurricane Center Miami FL AL202023
1100 PM AST Sat Oct 21 2023

Air Force and NOAA Hurricane Hunter aircraft data, along with radar
imagery from Guadeloupe, indicate that the center of Tammy passed
over the island of Barbuda a couple of hours ago. The hurricane
continues to produce intense convection in a small CDO feature with
some ill-defined bands north and northeast of the center. The
eyewall has generally not been closed on the radar images. There
are still some areas of strong convection affecting portions of the
Lesser Antilles to the south of Tammy. Flight-level and SFMR winds
along with Doppler velocity data suggested that the maximum winds
had decreased slightly, but there was an unofficial report of a
sustained wind of 78 kt from Barbuda. Based on a blend of the
aircraft data and the Barbuda observation, the intensity is held at
75 kt for this advisory.

Center fixes indicate that the hurricane continues on its
north-northwestward trek with an estimated motion of 330/9 kt. Over
the next couple of days, Tammy should turn northward while it moves
along the western side of a large subtropical high. Then, the
system should turn, at least temporarily, northeastward on the
southeastern periphery of a mid-tropospheric trough over the western
Atlantic. Beginning around 3 days, the track forecast becomes
challenging, since the global models indicate that the western
Atlantic trough will bypass Tammy after 72 hours while it continues
eastward. A ridge could then build in to the northwest of the
system and cause it to turn to the left. As noted earlier, there is
a very large spread in the track guidance in the latter part of the
forecast period. There is low confidence in the 4- and 5-day NHC
forecast positions.

Tammy should remain over very warm waters with moderate vertical
wind shear for the next couple of days. So, some slight
strengthening is still forecast. By 60 or 72 hours, increasing
shear is likely to induce a weakening trend. The official intensity
forecast is similar to the latest Decay-SHIPS guidance.


KEY MESSAGES:

1. Hurricane and tropical storm conditions are expected in portions
of the northern Leeward Islands through early Sunday.

2. The heaviest rains from Tammy will continue over the Leeward
Islands through Sunday. This rainfall may produce isolated flash and
urban flooding, along with isolated mudslides in areas of higher
terrain.

3. A storm surge could produce coastal flooding in areas of onshore
winds as the center of Tammy moves near or over the Leeward Islands.
Near the coast, the surge will be accompanied by large and dangerous
waves.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0300Z 17.8N 61.9W 75 KT 85 MPH
12H 22/1200Z 18.8N 62.5W 75 KT 85 MPH
24H 23/0000Z 20.2N 63.4W 80 KT 90 MPH
36H 23/1200Z 21.5N 63.9W 80 KT 90 MPH
48H 24/0000Z 22.6N 63.8W 80 KT 90 MPH
60H 24/1200Z 23.1N 63.6W 80 KT 90 MPH
72H 25/0000Z 23.5N 63.0W 75 KT 85 MPH
96H 26/0000Z 25.0N 62.5W 70 KT 80 MPH
120H 27/0000Z 27.5N 63.5W 60 KT 70 MPH

$$
Forecaster Pasch

[cycloneye]

Hurricane Tammy Discussion Number 16
NWS National Hurricane Center Miami FL AL202023
500 AM AST Sun Oct 22 2023

Tammy is beginning to pull away form the northernmost Leeward
islands this morning. The final fix of the prior Air Force
reconnaissance mission suggested the pressure was holding steady
with an eyewall that remained open to the southwest. This structure
was also consistent with the last few radar images out of Guadeloupe
as the Tammy moved out of its range. On satellite, the storm
continues to produce a compact central dense overcast (CDO) of deep
convection with overshooting cloud tops as cold as -85 to -90 C.
However moderate southwesterly vertical wind shear still appears to
be keeping the small hurricane in check with a sharp edge to its CDO
on the west side. The initial intensity is held at 75 kt this
advisory, which is a little under the subjective Dvorak
classifications form TAFB and SAB given the earlier aircraft data.
Another set of Air Force Reserve C-130 and NOAA-P3 aircraft are set
to sample the hurricane again later this morning.

The last center fix from the overnight Air Force mission suggested
that, after a brief west-northwest jog, Tammy had resumed a more
north-northwest motion, at 335/9 kt. Tammy should maintain this
motion or turn more northward during the remainder of today as it
moves along the western periphery of a large subtropical ridge. A
mid-latitude trough passing to the north of Tammy should then
position this ridge a bit southeast of the hurricane, and the
guidance shows Tammy responding by moving slowly north-northeastward
on Monday and Tuesday. However, most of the mid-latitude trough is
forecast to bypass the system, and this is where the guidance shows
dramatically increasing track spread. Most of the deterministic
models now show a deep-layer cutoff low breaking off from the
mid-latitude trough and dropping down to the west of Tammy, and the
vertical depth of the tropical cyclone will likely dictate how much
influence the cutoff low has on it. Much of the deterministic
guidance shows Tammy swinging around this cutoff and pivoting back
to the north or northwest by the end of the forecast period. The NHC
track forecast has been shifted a bit east and north of the prior
one, towards the consensus aids TVCN and HCCA. However the leftward
turn at the end of the forecast happens at a variety of different
latitudes in the GFS and ECMWF ensemble guidance. Thus, the track
forecast towards the end of the period is highly uncertain and of
low confidence.

As has been the case for the last couple of days, Tammy remains in
an environment of moderate 15-20 kt of southwesterly shear but
remains over warm 29-30 C sea-surface temperatures. That has not
prevented gradual intensification of the hurricane thus far, and so
some additional intensification is forecast over the next day or so.
Afterwards as the shear begins to gradually increase, there will
likely be some inner core fluctuations and the NHC intensity
forecast shows a leveling off of Tammy during this period. After 72
h, the shear is likely to become prohibitively strong and weakening
is forecast to begin by that time, with Tammy likely dropping under
hurricane intensity sometime in the day 4-5 period. The significant
shear forecast however may be offset by some baroclinic forcing of
the upper-level trough interacting with Tammy at the end of the
period. However, like the track forecast, there is a range of
intensity solutions at these latter time periods, with the NHC
intensity forecast most closely following the consensus aids HCCA
and IVCN.


KEY MESSAGES:

1. Hurricane conditions and coastal flooding in portions of the
northern Leeward Islands within the warning area should continue
for the next few hours.

2. The heaviest rains from Tammy will continue over the Leeward
Islands through today. This rainfall may produce isolated flash and
urban flooding, along with isolated mudslides in areas of higher
terrain.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0900Z 18.5N 62.3W 75 KT 85 MPH
12H 22/1800Z 19.5N 62.9W 80 KT 90 MPH
24H 23/0600Z 20.8N 63.5W 85 KT 100 MPH
36H 23/1800Z 21.9N 63.5W 85 KT 100 MPH
48H 24/0600Z 22.7N 63.1W 80 KT 90 MPH
60H 24/1800Z 23.2N 62.5W 80 KT 90 MPH
72H 25/0600Z 23.8N 61.9W 80 KT 90 MPH
96H 26/0600Z 26.0N 61.4W 70 KT 80 MPH
120H 27/0600Z 29.0N 62.5W 60 KT 70 MPH

$$
Forecaster Papin

[cycloneye]

Hurricane Tammy Discussion Number 19
NWS National Hurricane Center Miami FL AL202023
1100 PM AST Sun Oct 22 2023

Satellite images show that Tammy has not become better organized
over the past several hours. In fact, the Central Dense Overcast
(CDO) has become more fragmented in appearance and the center
appears to be near the southern portion of the CDO. There are
however a couple of prominent convective bands over the eastern
portion of the circulation. Upper-level outflow is restricted over
the southern semicircle of the system, suggesting the influence of
southerly vertical wind shear. SFMR-observed surface winds from a
NOAA Hurricane Hunter aircraft conducting a research mission into
Tammy support a current intensity of 70-75 kt, so the advisory
intensity estimate is unchanged.

A center position estimate from the aircraft indicates that the
motion remains northwestward, or 325/8 kt at this time. The
cyclone should turn northward to northeastward over the next 72
hours or so while moving around the western side of a mid-level
subtropical high. Later in the forecast period, Tammy should begin
to interact with a cyclonic circulation that cuts off from an
eastward-moving mid-latitude trough over the western Atlantic.
This should cause the system to turn westward around the northern
side of the larger circulation in 3-5 days. There continues to be
a fairly large spread in the track guidance in this time frame,
however.

The dynamical guidance indicates that Tammy will be in an
environment of significant south-southwesterly vertical wind shear
for the next few days. This negative influence could be
counteracted somewhat by the presence of a moist and unstable
air mass along with warm ocean waters. Therefore some slight
strengthening is still predicted, along the lines of the
Decay-SHIPS model. This is also similar to the previous official
intensity forecast. By day 4, Tammy should begin to merge with a
baroclinic zone and simulated satellite imagery from the GFS and
ECMWF models depict a frontal appearance. Therefore the system is
forecast to have become extratropical by 96 hours.


KEY MESSAGES:

1. Heavy rain from Tammy will remain possible over the British
Virgin Islands, Leeward Islands, and northern Windward Islands into
Monday morning. This rainfall may produce isolated flash and urban
flooding, along with isolated mudslides in areas of higher terrain.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0300Z 20.8N 64.0W 75 KT 85 MPH
12H 23/1200Z 21.5N 63.9W 75 KT 85 MPH
24H 24/0000Z 22.5N 63.4W 80 KT 90 MPH
36H 24/1200Z 23.2N 62.6W 80 KT 90 MPH
48H 25/0000Z 24.0N 61.6W 80 KT 90 MPH
60H 25/1200Z 25.3N 60.4W 80 KT 90 MPH
72H 26/0000Z 26.6N 59.5W 75 KT 85 MPH
96H 27/0000Z 29.6N 60.5W 60 KT 70 MPH...POST-TROP/EXTRATROP
120H 28/0000Z 30.5N 64.5W 50 KT 60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch

[cycloneye]

Hurricane Tammy Discussion Number 20
NWS National Hurricane Center Miami FL AL202023
500 AM AST Mon Oct 23 2023

Tammy's structure overnight appears to have undergone an evolution.
After maintaining a small compact presentation for several days,
Tammy's convective structure has broadened out, with convective
bands taking on a more fragmented appearance around the center. Some
of this change could be related to some dry air that may have been
entrained into the circulation earlier tonight. On the other hand,
the upper-level outflow has expanded some to the south and west,
suggesting a brief respite in the shear that has been affecting
Tammy. Data from the last pass of the NOAA-P3 reconnaissance mission
suggested the winds were perhaps a bit lower, while both subjective
and objective satellite estimates were also somewhat lower than
earlier. The initial intensity was nudged downward to 70 kt this
advisory.

Tammy has made the long awaited turn northward, with the estimated
motion now at 355/9 kt. A continued turn to the north-northeast and
northeast is anticipated over the next 24-36 hours as the hurricane
briefly becomes steered in between a mid-latitude trough passing by
to its north, and an established mid-level ridge located to its
east. The track guidance is at least in good agreement on this track
evolution for the first 48-60 h. After that time, a piece of the
aforementioned trough is expected to cutoff and dig southward to the
west of Tammy. How the tropical cyclone reacts to this synoptic
feature will likely be dependent on its vertical depth, and its
location when the trough interacts with it. If anything, the track
guidance spread is even larger than it was a few cycles ago, with a
range of solutions from a quick pivot back west (the HAFS-A/B runs)
after 60 h versus a continued northeastward track without much of a
leftward turn at all (the latest GFS forecast). Overall the track
consensus aids have shifted a bit more poleward before Tammy turns
westward, and the NHC track was shifted a little further east and
north compared to the prior one. However, this track forecast
remains of low confidence and is highly uncertain, which is best
exemplified by the 00 UTC ECMWF ensemble guidance, which shows more
than a 1500 mile southwest-to-northeast spread in the various member
solutions in 5 days.

Tammy's somewhat broader structure could delay some intensification
in the immediate short-term, but most of the intensity guidance
remains adamant about some strengthening occuring in the next 24-36
h as the hurricane remains over 28-29 C sea-surface-temperatures and
moderate wind shear between 15-20 kt. However after 48 hours,
vertical wind shear is expected to rapidly increase out of the
southwest which should begin to weaken the tropical cyclone. This
forecast remains near or just a bit below the consensus aids HCCA
and IVCN during this time frame. After 72 h, The cutoff trough
digging in to the west of Tammy will likely impart some cool and
very dry mid-latitude air into the storm's core, initiating
extratropical transition as deep central convection is also stripped
away by the increased shear. This process could be completed in 96
h, especially if Tammy moves further north like the GFS and ECMWF
models are forecasting. However, there also remains some uncertainty
about this evolution, as a further south track before the storm
pivots west could allow it to remain over warmer sea-surface
temperatures and potentially prevent extratropical transition from
completing, as suggested by the HAFS-A/B runs.

Even as Tammy moves away from the Leeward islands, a prominent
feeder band has formed over these islands, likely prolonging the
heavy rain threat for these areas through this morning.


KEY MESSAGES:

1. Heavy rain from Tammy will remain possible over the British
Virgin Islands, Leeward Islands, and northern Windward Islands
through this morning. This rainfall may produce isolated flash and
urban flooding, along with isolated mudslides in areas of higher
terrain.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 21.4N 64.0W 70 KT 80 MPH
12H 23/1800Z 22.2N 63.7W 70 KT 80 MPH
24H 24/0600Z 23.2N 62.9W 75 KT 85 MPH
36H 24/1800Z 24.1N 61.7W 80 KT 90 MPH
48H 25/0600Z 25.1N 60.5W 80 KT 90 MPH
60H 25/1800Z 26.5N 59.3W 75 KT 85 MPH
72H 26/0600Z 28.0N 58.7W 65 KT 75 MPH
96H 27/0600Z 30.4N 59.4W 55 KT 65 MPH...POST-TROP/EXTRATROP
120H 28/0600Z 32.0N 62.9W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin

[cycloneye]

Hurricane Tammy Discussion Number 21
NWS National Hurricane Center Miami FL AL202023
1100 AM AST Mon Oct 23 2023

Tammy appears to be holding steady in spite of the moderate
southwesterly vertical wind shear. There have been regular bursts
of deep convection over the center and a fragmented band around the
eastern portion of the circulation. The latest intensity is held at
70 kt to represent a blend of the subjective satellite intensity
estimates from TAFB and SAB, which were 77 kt and 65 kt,
respectively.

The hurricane is moving northward at 005/6 kt. Tammy should
continue to turn north-northeastward to northeastward in the flow
between a mid-latitude trough over the western Atlantic and a
mid-level ridge over the central subtropical Atlantic. Beyond 60 h,
there is still a significant spread in the model guidance. Most of
the regional models and the GFS model forecast Tammy to continue
northward around the western side of the ridge. A different cluster
of model solutions, including the ECMWF, merge Tammy with a cutoff
low that forms from the trough and turns the cyclone northwestward
to westward. The latest NHC track forecast favors the latter
scenario and has been nudged slightly north of the previous
prediction.

Southwesterly shear appears to be influencing Tammy's structure.
The vertical wind shear is expected to persist and likely increase
in about 36 h, forcing some dry mid-level air into the cyclone's
circulation. These environmental conditions should lead to gradual
weakening. Model guidance predicts that Tammy should undergo
structural changes over the next couple of days as it interacts with
the aforementioned cutoff low. The latest official intensity
forecast now shows Tammy becoming extratropical in 72 hours.


KEY MESSAGES:

1. Heavy rain from Tammy will remain possible over the British
Virgin Islands and Leeward Islands through today. This rainfall may
produce isolated flash and urban flooding, along with isolated
mudslides in areas of higher terrain.


FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 21.9N 63.9W 70 KT 80 MPH
12H 24/0000Z 22.7N 63.4W 70 KT 80 MPH
24H 24/1200Z 23.6N 62.4W 75 KT 85 MPH
36H 25/0000Z 24.5N 61.2W 80 KT 90 MPH
48H 25/1200Z 25.8N 59.9W 75 KT 85 MPH
60H 26/0000Z 27.3N 58.9W 70 KT 80 MPH
72H 26/1200Z 29.1N 58.6W 60 KT 70 MPH...POST-TROP/EXTRATROP
96H 27/1200Z 31.2N 60.2W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 28/1200Z 32.4N 63.6W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci

[cycloneye]

918
WTNT45 KNHC 232039
TCDAT5

Hurricane Tammy Discussion Number 22
NWS National Hurricane Center Miami FL AL202023
500 PM AST Mon Oct 23 2023

Moderate southwesterly vertical wind shear seems to be disrupting
Tammy's circulation. Deep convection is being pulled northward away
from the estimated low-level center and mid-level dry air is working
its way around the southern side of the cyclone. Satellite
intensity estimate have decreased this cycle to 55 and 65 kt from
SAB and TAFB, respectively. The initial intensity has therefore
been lowered to 65 kt. While ASCAT missed the majority of the
hurricane's core, it did show winds on the western portion of the
circulation have decreased and the radii have been adjusted inward
accordingly.

Tammy is moving north-northeastward at 6 kt. A turn toward the
northeast is forecast shortly as Tammy is steered by a mid-level
ridge centered over the central subtropical Atlantic and the flow
ahead of a mid-latitude trough over the western Atlantic. Between
48-60 h, the model solutions begin to bifurcate. The ECMWF turns
the hurricane northward and then westward by the end of the forecast
period. The GFS and regional models tend to turn Tammy toward the
north and northeastward by day 5. The official forecast still
favors the ECMWF forecast and is similar to the previous advisory.

Models suggest that environmental conditions will be relatively
unfavorable. The deep-layer vertical wind shear is forecast to
increase and surrounding mid-level moisture to decrease through most
of the forecast period. However, in a day or so, when the hurricane
begins to interacts with the trough to its west, upper-level
divergence could enhance convection and cause some strengthening
through about 48 h. Tammy is then expected to gradually weaken and
complete its transition into an extratropical cyclone by day 3. The
NHC intensity forecast is similar to the previous prediction, with a
slightly lower peak intensity of 75 kt.


FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 22.3N 63.6W 65 KT 75 MPH
12H 24/0600Z 23.0N 62.9W 70 KT 80 MPH
24H 24/1800Z 24.0N 61.7W 75 KT 85 MPH
36H 25/0600Z 25.3N 60.3W 75 KT 85 MPH
48H 25/1800Z 26.8N 59.0W 75 KT 85 MPH
60H 26/0600Z 28.9N 58.6W 70 KT 80 MPH
72H 26/1800Z 30.3N 59.3W 60 KT 70 MPH...POST-TROP/EXTRATROP
96H 27/1800Z 31.7N 62.1W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 28/1800Z 32.5N 65.2W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci

[cycloneye]

Hurricane Tammy Discussion Number 23
NWS National Hurricane Center Miami FL AL202023
1100 PM AST Mon Oct 23 2023

Microwave data from multiple polar-orbiting satellites received
during the last few hours indicate that Tammy still has a
well-organized low- to mid-level circulation, even as its deep
convection is getting sheared northward. The most recent TAFB Dvorak
classification was a 4.0/65 kt, which supports maintaining Tammy as
a hurricane.

While Tammy's future path remains unusually unclear, especially at
the 4-5 day range, very little change was made to the official track
forecast. The hurricane is currently moving north-northeastward, and
it should get steered northward starting in about 2 days as the
hurricane interacts with a mid-latitude trough approaching from the
northwest. The uncertainty in the forecast increases considerably
after that point as Tammy will likely reach a col point in the
steering flow over the western Atlantic. Many models and ensemble
members indicate another mid-latitude trough will cause the cyclone
to begin to accelerate eastward or northeastward. However, it
appears equally likely that Tammy will then turn westward or
southwestward under the influence of a mid-level ridge that
should build behind the second trough. With no clear reason to
support one solution or another, the NHC track forecast is unchanged
for now. It remains near the consensus of the GFS and ECMWF through
about 72 h, and then favors the ECMWF and ECENS mean after that.

Conversely, the intensity forecast appears to be more
straightforward. Most of the intensity guidance indicates that
slight strengthening is possible during the next day or so, as Tammy
gets a convective boost while interacting with an upper-level
trough. However, after about 48 h, it should begin to weaken and
transition to a post-tropical cyclone. Based on simulated satellite
imagery, this process is expected to complete in about 72 h, though
Tammy will likely continue to produce gale- to storm-force winds for
several days thereafter.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 22.9N 63.1W 65 KT 75 MPH
12H 24/1200Z 23.6N 62.2W 70 KT 80 MPH
24H 25/0000Z 24.7N 60.8W 75 KT 85 MPH
36H 25/1200Z 26.5N 59.2W 75 KT 85 MPH
48H 26/0000Z 28.5N 58.3W 75 KT 85 MPH
60H 26/1200Z 30.0N 58.6W 65 KT 75 MPH
72H 27/0000Z 31.1N 59.7W 55 KT 65 MPH...POST-TROP/EXTRATROP
96H 28/0000Z 32.0N 62.0W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 29/0000Z 32.5N 64.0W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster D. Zelinsky

[cycloneye]

Hurricane Tammy Discussion Number 24
NWS National Hurricane Center Miami FL AL202023
500 AM AST Tue Oct 24 2023

Tammy's satellite depiction has improved slightly compared to the
sheared convective pattern from yesterday evening. The latest
infrared satellite imagery depicts convective bursts are once again
wrapping around the southern portion of the system. Earlier
microwave imagery showed a well organized low-to mid-level
circulation. The most recent TAFB Dvorak satellite estimate held
steady at T4.0/65kt, which supports maintaining an initial intensity
of 65 kt for this advisory.

The hurricane is currently moving northeastward, and should
continue this motion for the next day or two. A mid-latitude trough
approaching the system from the northwest will cause Tammy to begin
to move more northward during the middle of the forecast period. It
is after this point, the model guidance becomes increasingly
divergent. Models are split on whether another mid-latitude trough
will cause the system to accelerate east to northeastward, or have
Tammy not being picked up by this trough and move the system
westward to southwestward under a building mid-level ridge. The GFS
has trended towards the west-southwest track scenario, closer to
the ECMWF. Therefore, the NHC forecast track, which already favored
the ECMWF solution, remains similar to the previous advisory and is
close to a blend of GFS and ECMWF.

There is considerably better agreement among most of the
intensity guidance, which indicates slight strengthening is possible
during the next day or two, as Tammy interacts with an upper-level
trough. After 48 hours the system should begin to weaken and
start to transition into a post-tropical cyclone. The latest model
simulated satellite imagery depicts that this process is expected
to be complete in about 60 h, though Tammy will likely continue to
produce gale-to storm-force winds for several days even after this
transition occurs.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 23.7N 62.8W 65 KT 75 MPH
12H 24/1800Z 24.5N 61.8W 70 KT 80 MPH
24H 25/0600Z 25.9N 60.3W 75 KT 85 MPH
36H 25/1800Z 27.9N 59.0W 75 KT 85 MPH
48H 26/0600Z 29.5N 58.9W 70 KT 80 MPH
60H 26/1800Z 31.0N 59.7W 60 KT 70 MPH...POST-TROP/EXTRATROP
72H 27/0600Z 31.7N 60.9W 55 KT 65 MPH...POST-TROP/EXTRATROP
96H 28/0600Z 32.4N 62.8W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 29/0600Z 32.8N 64.8W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Kelly

[cycloneye]

Hurricane Tammy Discussion Number 25
NWS National Hurricane Center Miami FL AL202023
1100 AM AST Tue Oct 24 2023

The hurricane has held steady this morning. Satellite imagery
depicts deep bursts of convection mainly to the north of the center
and a large curved band around the northern and eastern portions of
the system. The most recent TAFB Dvorak satellite estimate is still
T4.0/65kt, and the initial intensity remains at 65 kt for this
advisory.

Tammy is moving northeastward with an estimated motion of 035/6 kt.
A mid-latitude trough over the northwestern Atlantic should steer
the hurricane more northward in a day or so. By day 2, most of the
global model guidance shows Tammy turning westward and slowing down
between two mid-level ridges through the remainder of the forecast
period. Only minor adjustments have been made in the latest NHC
track prediction, which lies in the middle of the track guidance
envelope.

Intensity guidance continues to suggest Tammy should slightly
strengthen in the near term. As the hurricane approaches the
mid-latitude trough, it should enter a region with enhanced
upper-level divergence, and thus strengthen. After about a day or
so, strong deep-layer vertical wind shear and cooling sea surface
temperatures should gradually weaken the cyclone. Tammy is still
expected to become a gale-force extratropical cyclone by 60 h.


FORECAST POSITIONS AND MAX WINDS

INIT 24/1500Z 24.2N 62.3W 65 KT 75 MPH
12H 25/0000Z 25.0N 61.2W 70 KT 80 MPH
24H 25/1200Z 26.7N 59.9W 75 KT 85 MPH
36H 26/0000Z 28.6N 59.1W 70 KT 80 MPH
48H 26/1200Z 30.1N 59.5W 65 KT 75 MPH
60H 27/0000Z 31.2N 60.6W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 27/1200Z 31.8N 61.6W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 28/1200Z 32.5N 63.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 29/1200Z 32.6N 65.1W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci

[cycloneye]

Hurricane Tammy Discussion Number 26
NWS National Hurricane Center Miami FL AL202023
500 PM AST Tue Oct 24 2023

There have not been many changes in the satellite appearance of
Tammy since the previous advisory. Bursts of convection continue to
wrap around the estimated surface center. An AMSR2 microwave
satellite pass at 1657 UTC showed a closed low-level circulation.
While a couple of ASCAT passes showed surface winds less than
hurricane strength, the resolution of the instrument likely cannot
capture the peak winds in Tammy's small inner core. The initial
intensity is held at 65 kt, closest to the TAFB satellite intensity
estimate, though this could be generous.

Simulated satellite imagery suggests Tammy could strengthen slightly
within a day or so when the hurricane enters a region of enhanced
upper-level divergence. Beyond this time frame, strong
southwesterly shear, dry mid-level relative humidities, and cooling
sea surface temperatures should cause Tammy to steadily weaken.
Global models now indicate the hurricane should transition into a
gale-force extratropical cyclone by 48 h, and this is reflected in
the official intensity prediction.

Tammy is moving to the northeast at about 7 kt. A mid-latitude
trough should turn the hurricane north-northeastward and northward
in a day or so. By Thursday, Tammy should bend to the northwest and
slow down within the light steering currents between two ridges. A
gradual westward turn is expected by the end of the forecast period.
The latest NHC track prediction is slightly to the south of the
previous advisory, and forward speed in the long-term forecast has
been slowed.


FORECAST POSITIONS AND MAX WINDS

INIT 24/2100Z 24.6N 61.7W 65 KT 75 MPH
12H 25/0600Z 25.6N 60.7W 70 KT 80 MPH
24H 25/1800Z 27.5N 59.6W 70 KT 80 MPH
36H 26/0600Z 29.2N 59.4W 65 KT 75 MPH
48H 26/1800Z 30.4N 60.3W 55 KT 65 MPH...POST-TROP/EXTRATROP
60H 27/0600Z 31.1N 61.2W 50 KT 60 MPH...POST-TROP/EXTRATROP
72H 27/1800Z 31.6N 62.2W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 28/1800Z 32.0N 63.4W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 29/1800Z 32.0N 64.4W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci

[cycloneye]

Hurricane Tammy Discussion Number 27
NWS National Hurricane Center Miami FL AL202023
1100 PM AST Tue Oct 24 2023

Satellite data indicate Tammy has strengthened tonight. Deep
convection has increased near and over the center of the hurricane
during the past several hours, resulting in a cold and expanding
central dense overcast with intermittent glimpses of a ragged eye.
Recent SSMIS and GMI passive microwave images show a tighter inner
core compared to earlier today, with a mid-level eyewall that mostly
wraps around the center. The subjective Dvorak estimates from SAB
and TAFB have risen to T4.5/77 kt and T4.0/65 kt, respectively, with
similar increases in the various UW-CIMSS objective estimates. Thus,
the initial intensity is raised to 75 kt for this advisory.

Despite strengthening upper-level winds over Tammy, increasing
upper-level divergence associated with a deep-layer trough over the
western Atlantic could support some additional intensification in
the near term, as shown by the GFS and some of the regional models.
Given recent trends, the updated NHC intensity forecast is raised at
12-24 h to account for this potential. Then, Tammy is expected to
merge with a cold front currently analyzed to the northwest of the
hurricane. This extratropical transition is forecast to be completed
by 36 h, with an expansion of Tammy's wind field as it becomes a
hurricane-force extratropical cyclone. Thereafter, the global models
show the frontal cyclone weakening through the rest of the period.
There is some potential it could shed its frontal structure this
weekend, but for now the model-simulated satellite imagery does not
show much increase in convection during that time.

Tammy is moving northeastward (50 degrees/8 kt) within the flow
between a deep-layer trough over the western Atlantic and a
subtropical ridge over the central Atlantic. Tammy is expected to
turn northward during the next day or so as it becomes captured by
the upper trough. The updated NHC forecast lies slightly right of
the previous one in the first 24 h, mostly based on the more
northeastward initial position. Then, the cyclone is forecast to
move more slowly northwestward in 2-3 days within weaker steering
currents. The long-range track forecast is highly uncertain, with
diverging global and ensemble model solutions that move the
shallower cyclone in opposite directions. Given the above-average
uncertainty, it seems prudent to make little change to this portion
of the track forecast at this time.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 24.9N 60.7W 75 KT 85 MPH
12H 25/1200Z 26.1N 59.9W 85 KT 100 MPH
24H 26/0000Z 28.1N 59.1W 80 KT 90 MPH
36H 26/1200Z 29.6N 59.7W 70 KT 80 MPH...POST-TROP/EXTRATROP
48H 27/0000Z 30.5N 60.9W 60 KT 70 MPH...POST-TROP/EXTRATROP
60H 27/1200Z 30.9N 61.8W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 28/0000Z 31.3N 62.7W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 29/0000Z 31.4N 63.6W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 30/0000Z 31.0N 64.5W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Reinhart

[cycloneye]

Hurricane Tammy Discussion Number 28
NWS National Hurricane Center Miami FL AL202023
500 AM AST Wed Oct 25 2023

Satellite data indicate Tammy has strengthened this morning.
Proxy-vis and infrared imagery depict a ragged eye has developed
with deep convection wrapping around the center. There has been no
microwave imagery this morning, but earlier SSMI/S and GMI
images showed a tight inner core. The subjective Dvorak final-T
intensity estimates have increased this cycle with a T5.0 and T4.5
from SAB and TAFB, respectively. Given the improved satellite
imagery and using a blend of these estimates, the initial intensity
is raised to 85 kt for this advisory.

Although vertical wind shear is analyzed to have increased over
the hurricane, the system is strengthening beneath upper-level
divergence associated with a deep-layer trough over the western
Atlantic. Models suggest some additional strengthening is possible
over the next 12 hours or so, which is reflected in the NHC
intensity forecast. Tammy is then expected to merge with a cold
front, which is currently analyzed by TAFB and OPC just northwest of
the system. Tammy is expected to undergo an extratropical
transition, with this transition forecast to be complete within 24
hours. As this transition occurs Tammy's wind field will expand as
it becomes a hurricane-force extratropical cyclone. Global models
are in fairly good agreement that the cyclone will then weaken
throughout the remainder of the forecast period. There is some
potential it could shed its frontal structure this weekend, but for
now the model-simulated satellite imagery does not show much
increase in convection during that time.

Tammy is moving northeastward at an estimated motion of 45 degrees
at 9 knots, within the flow between a deep-layer trough over the
western Atlantic and a subtropical ridge over the central Atlantic.
Tammy is expected to turn northward later today, then move slowly
northwestward in 2-3 days within weaker steering currents. The
long-range forecast remains uncertain, with not much run-to-run
model consistency and ensemble solutions that move in opposite
directions. Given the uncertainty, there is little change from the
previous forecast at this time range, with the NHC forecast track
showing the cyclone slowing and meandering through the end of the
the period.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 25.6N 60.2W 85 KT 100 MPH
12H 25/1800Z 27.0N 59.4W 90 KT 105 MPH
24H 26/0600Z 28.9N 59.3W 75 KT 85 MPH...POST-TROP/EXTRATROP
36H 26/1800Z 30.0N 60.4W 65 KT 75 MPH...POST-TROP/EXTRATROP
48H 27/0600Z 30.6N 61.6W 60 KT 70 MPH...POST-TROP/EXTRATROP
60H 27/1800Z 31.0N 62.3W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 28/0600Z 31.3N 62.9W 50 KT 60 MPH...POST-TROP/EXTRATROP
96H 29/0600Z 31.2N 63.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 30/0600Z 31.0N 63.9W 40 KT 45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Kelly

[cycloneye]

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]

Hurricane Tammy Discussion Number 30
NWS National Hurricane Center Miami FL AL202023
500 PM AST Wed Oct 25 2023

Tammy is beginning to interact with a front to its north. The eye
has lost some of its definition as the northern eyewall slowly
erodes. Outflow is now limited to the southern and eastern portions
of the circulation. Subjective and objective satellite intensity
estimates have fallen since the last advisory. Final T-numbers from
SAB and TAFB are both T4.5 and ADT is down to T4.2. Given the recent
degradation in satellite appearance, the initial intensity has been
lowered to 85 kt.

It appears that Tammy has moved out of the region with favorable
upper-level dynamics. Strong upper-level winds and surrounding dry
air are expected to steadily weaken the system through the forecast
period. Model guidance shows that the hurricane should become
entangled with the frontal feature to its north and transition into
an extratropical cyclone within the next 24 hours. By 48 hours, the
global models depict Tammy occluding and shedding its front.
Therefore, the most recent NHC forecast shows the system as a
post-tropical cyclone instead of extratropical beginning at day 2.
There is a possibility that Tammy could regain tropical or
subtropical status as the vortex meanders over sufficiently warm
ocean waters during days 2 and 3.

Tammy is still moving northeastward, but model guidance insists that
the hurricane will make a turn to the north shortly. This is
followed by a northwestward turn with a slower forward speed by
Thursday. 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 official NHC track forecast shows Tammy slowly turning
back to the east by the weekend. However, more model guidance is
showing a faster turn to the east resulting in a large spread in the
track guidance envelope. The current forecast is on the western edge
of the track solutions and is closest to the GFS. Further
adjustments may be needed if these trends continue.


FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 28.0N 57.9W 85 KT 100 MPH
12H 26/0600Z 29.5N 58.4W 80 KT 90 MPH
24H 26/1800Z 30.5N 59.4W 70 KT 80 MPH...POST-TROP/EXTRATROP
36H 27/0600Z 31.1N 60.4W 60 KT 70 MPH...POST-TROP/EXTRATROP
48H 27/1800Z 31.5N 61.1W 55 KT 65 MPH...POST-TROPICAL
60H 28/0600Z 31.8N 61.5W 50 KT 60 MPH...POST-TROPICAL
72H 28/1800Z 32.1N 61.7W 50 KT 60 MPH...POST-TROPICAL
96H 29/1800Z 32.5N 61.5W 45 KT 50 MPH...POST-TROPICAL
120H 30/1800Z 32.8N 61.0W 40 KT 45 MPH...POST-TROPICAL

$$
Forecaster Bucci/R. Zelinsky

[cycloneye]

Post-Tropical Cyclone Tammy Discussion Number 32
NWS National Hurricane Center Miami FL AL202023
500 AM AST Thu Oct 26 2023

Tammy appears to have completed its transition to a post-tropical
cyclone, merging with the nearby front. The cloud pattern has become
more comma shaped, with a long linear convective band, and is no
longer producing deep convection near the center. The cyclone is
now frontal but likely still has a warm core, indicating that it is
a warm seclusion-type of extratropical cyclone. Despite the
transition, it remains a strong cyclone, and the initial intensity
is 75 kt, based on current intensity satellite estimates.

The cyclone has slowed down and made a northward turn overnight, and
recently the system is turning more north-northwestward. The
estimated long-term motion is 355/10 kt. Over the next day or so,
Tammy is forecast to slow down and move generally northwestward to
west-northwestward. Beyond 36 h there continues to be high
uncertainty in the track forecast, with no more clarity from the
latest global model runs. The global models continue to have
enormous spread, and ensemble solutions that diverge in opposite
directions. Given the uncertainty, there is little change from the
previous forecast at this time range.

Although post-tropical, Tammy remains a powerful cyclone. In the
near term, the increasing shear and drier air associated with a
deep-layer trough to the west should continue to cause convection to
dissipate, and the system to weaken over the next few days. Global
model fields indicate Tammy could shed its frontal structure by 36
h. A reduction in wind shear is forecast soon thereafter, and
convection could redevelop near Tammy's center in about 2-3 days
while it moves over 25-26C sea surface temperatures. 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.

This is the last NHC advisory. Additional information on this system
can be found in High Seas Forecasts issued by the National Weather
Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and
online at ocean.weather.gov/shtml/NFDHSFAT1.php


FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 30.5N 58.4W 75 KT 85 MPH...POST-TROP/EXTRATROP
12H 26/1800Z 31.2N 59.6W 65 KT 75 MPH...POST-TROP/EXTRATROP
24H 27/0600Z 31.5N 61.0W 55 KT 65 MPH...POST-TROP/EXTRATROP
36H 27/1800Z 31.9N 62.2W 55 KT 65 MPH...POST-TROPICAL
48H 28/0600Z 32.3N 62.1W 50 KT 60 MPH...POST-TROPICAL
60H 28/1800Z 32.4N 61.2W 50 KT 60 MPH...POST-TROPICAL
72H 29/0600Z 32.4N 60.4W 45 KT 50 MPH...POST-TROPICAL
96H 30/0600Z 32.3N 59.6W 40 KT 45 MPH...POST-TROPICAL
120H 31/0600Z 32.2N 58.4W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Kelly

[cycloneye]

Tropical Storm Tammy Discussion Number 33
NWS National Hurricane Center Miami FL AL202023
1100 AM AST Fri Oct 27 2023

Tammy appears to have become separate from the frontal zone in
which it was formerly embedded. Satellite imagery shows that
moderately deep convection has developed in a fairly symmetrical
pattern near the center, and there are also convective bands
surrounding the center. This change in structure indicates that
the system has evolved back into a tropical cyclone, so advisories
are being re-initiated on Tammy. Extrapolation of earlier
scatterometer data suggest that the current intensity is around 55
kt.

Over the next few days, the atmospheric and oceanic environment
for Tammy should result in gradual weakening. The cyclone is
currently over marginal SSTs, and westerly vertical wind shear is
likely to increase. Later in the forecast period, Tammy will
probably move over slightly warmer waters, but dry air and strong
shear will likely cause continued weakening. The official
intensity forecast is on the high side of the model guidance and
shows the cyclone weakening to a depression in 5 days, although
given the environment this may occur sooner.

The storm is drifting slowly northwestward, with a motion near
320/3 kt. Tammy should turn eastward in 12 to 24 hours under the
influence of mid-level westerly flow on the north side of a
subtropical ridge. Later in the forecast period, the system is
expected to turn southeastward and southward on the eastern side of
a subtropical anticyclone and west of a broad trough over the
eastern Atlantic. The official forecast is similar to, but
somewhat slower than, the model consensus prediction and roughly in
the middle of the track guidance suite.

Gusty winds are expected in Bermuda through tonight, and a gale
warning is in effect for that island.


FORECAST POSITIONS AND MAX WINDS

INIT 27/1500Z 32.2N 61.1W 55 KT 65 MPH
12H 28/0000Z 32.4N 61.3W 55 KT 65 MPH
24H 28/1200Z 32.7N 59.9W 50 KT 60 MPH
36H 29/0000Z 32.5N 57.5W 45 KT 50 MPH
48H 29/1200Z 32.0N 54.5W 45 KT 50 MPH
60H 30/0000Z 30.7N 51.4W 40 KT 45 MPH
72H 30/1200Z 29.0N 50.0W 40 KT 45 MPH
96H 31/1200Z 27.5N 50.0W 35 KT 40 MPH
120H 01/1200Z 28.0N 51.0W 30 KT 35 MPH

$$
Forecaster Pasch

[cycloneye]

Tropical Storm Tammy Discussion Number 34
NWS National Hurricane Center Miami FL AL202023
500 PM AST Fri Oct 27 2023

Tammy's cloud pattern hasn't changed much on satellite images since
earlier today. There has been some cooling of the convective cloud
tops to about -60 deg C near the center of circulation along with a
few banding features. There is limited upper-level outflow to the
south and east of the system. The current intensity is held at 55
kt in agreement with an objective ADT Dvorak estimate from UW-CIMSS.

Tammy is currently situated over SSTs of around 25 deg C in a
marginally moist mid-level air mass. The dynamical guidance
indicates a significant increase in vertical wind shear during the
next day or so. This should cause a gradual weakening trend to
commence soon. Later in the forecast period, although the ocean
waters under Tammy should get a little warmer, strong shear and
substantially drier air should cause continued weakening. The
official intensity forecast is above most of the model guidance, so
Tammy could weaken to a depression sooner than shown here.

Tammy is currently moving slowly northwestward at about 320/3
kt. The cyclone should soon turn to an eastward track and move
along the northern side of a subtropical ridge for a couple of
days. Later in the forecast period, Tammy is expected to turn
southward and move along the eastern side of a mid-level high. The
official track forecast lies between the simple and corrected
dynamical model consensus solutions.


FORECAST POSITIONS AND MAX WINDS

INIT 27/2100Z 32.5N 61.4W 55 KT 65 MPH
12H 28/0600Z 32.7N 60.8W 50 KT 60 MPH
24H 28/1800Z 32.7N 59.0W 50 KT 60 MPH
36H 29/0600Z 32.3N 56.2W 45 KT 50 MPH
48H 29/1800Z 31.2N 53.4W 40 KT 45 MPH
60H 30/0600Z 30.0N 51.5W 35 KT 40 MPH
72H 30/1800Z 28.5N 51.0W 30 KT 35 MPH
96H 31/1800Z 28.0N 51.4W 25 KT 30 MPH
120H 01/1800Z 27.5N 52.0W 25 KT 30 MPH

$$
Forecaster Pasch

[cycloneye]

Tropical Storm Tammy Discussion Number 35
NWS National Hurricane Center Miami FL AL202023
1100 PM AST Fri Oct 27 2023

Strong southwesterly shear is taking a toll on Tammy tonight. Its
limited convection is confined to the northeastern portion of its
circulation, which is partially exposed in proxy-visible satellite
images. This shear has resulted in the vortex becoming vertically
tilted, with the mid-level center displaced to the northeast of the
low-level center in recent AMSR2 passive microwave images. Based on
these structural changes and the decreasing satellite intensity
estimates from TAFB and UW-CIMSS, the initial intensity is lowered
to 50 kt.

The deep-layer shear is expected to persist over Tammy during the
next few days, which should result in weakening while the storm
moves over marginal SSTs. While the forecast track does bring the
center of Tammy over warmer waters by early next week, the much
drier and more convergent upper-level environment should make it
difficult for Tammy to sustain organized convection. In fact, GFS
and ECMWF model-simulated satellite data indicate Tammy could be
completely devoid of convection within the next 2-3 days. The
updated NHC forecast is lower than the previous one, following the
latest IVCN and HCCA aids. Post-tropical remnant low status is shown
in 72 h, although this could occur even sooner than forecast.

The long-term motion of Tammy is north-northwestward (335/4 kt), but
recent satellite images indicate the cyclone is now turning
northward as anticipated. A faster eastward to southeastward motion
is forecast over the weekend as Tammy moves around the northern and
eastern sides of a mid-level ridge. Then, the weakening cyclone is
forecast to slow down and turn southward on Monday as the ridge
becomes positioned to its west. No major changes were made to the
NHC track forecast, which still lies between the simple and
corrected consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0300Z 32.7N 61.3W 50 KT 60 MPH
12H 28/1200Z 32.9N 60.3W 45 KT 50 MPH
24H 29/0000Z 32.6N 57.9W 40 KT 45 MPH
36H 29/1200Z 31.9N 55.0W 40 KT 45 MPH
48H 30/0000Z 30.5N 52.7W 35 KT 40 MPH
60H 30/1200Z 29.1N 51.6W 30 KT 35 MPH
72H 31/0000Z 28.2N 51.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 01/0000Z 28.1N 52.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 02/0000Z...DISSIPATED

$$
Forecaster Reinhart

[cycloneye]

Tropical Storm Tammy Discussion Number 36
NWS National Hurricane Center Miami FL AL202023
500 AM AST Sat Oct 28 2023

Tammy continues to be a sheared system with limited convection this
morning. Cloud tops have been warming since last evening, with only
occasional burst near the center. A partial scatterometer pass that
arrived shortly after the previous advisory, depicted winds on the
eastern side of the system were 40-45 knots. This ASCAT data is in
good agreement with the latest TAFB satellite intensity estimate of
T3.0/45 kt. Therefore, the initial intensity is lowered to 45 kt
based on this data and the degraded satellite presentation.

Strong vertical wind shear is expected to continue over Tammy the
next few days, which should result in further weakening. While sea
surface temperatures are marginal, there is increasingly dry air
along the forecast track. The GFS and ECMWF model-simulated
satellite data indicate Tammy could be completely devoid of
convection within 36- 48 hours. The updated NHC intensity forecast
is lower than the previous one, following the latest consensus aids.
Post-tropical remnant low status is now shown in 48 h, although this
could occur even sooner than forecast.

Tammy has turned northward and then northeastward overnight. The
long-term motion of Tammy is northeast at 50/6 kt. A faster eastward
to southeastward motion is forecast throughout the weekend as Tammy
moves around the northern and eastern sides of a mid-level ridge.
As the cyclone weakens and becomes more shallow it is forecast to
slow down and turn southward-southwestward early next week as the
ridge becomes positioned to its west. The NHC track forecast is a
little faster than the previous, and lies between the simple and
corrected consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 33.0N 60.1W 45 KT 50 MPH
12H 28/1800Z 33.0N 58.7W 40 KT 45 MPH
24H 29/0600Z 32.6N 56.0W 35 KT 40 MPH
36H 29/1800Z 31.7N 53.1W 35 KT 40 MPH
48H 30/0600Z 30.4N 50.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 30/1800Z 28.9N 49.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 31/0600Z 27.5N 50.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 01/0600Z 27.9N 53.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 02/0600Z...DISSIPATED

$$
Forecaster Kelly

[cycloneye]

Tropical Storm Tammy Discussion Number 37
NWS National Hurricane Center Miami FL AL202023
1100 AM AST Sat Oct 28 2023

Tammy has not changed much this morning. The impact of strong
westerly wind shear is evident, with an exposed low-level center
apparent in visible satellite imagery. Modest deep convection
remains confined to the eastern half of the circulation, and cloud
tops have continued to gradually warm. The subjective TAFB
satellite estimate of T3.0/45 kt and a blend of objective satellite
estimates continue to support an initial intensity of 45 kt for this
advisory.

Under the continued influence of strong shear for the next 48
hours, as well as a dry mid-level airmass approaching from the
northwest, Tammy is expected to continue weakening. Global and
regional models suggest that most of the deep convection will
diminish by late Sunday or Monday, at which time Tammy is forecast
to become a remnant low. The NHC forecast is similar to the prior
forecast and represents a blend of the prior forecast and intensity
consensus models.

Tammy has accelerated this morning and is now moving east-northeast
or 080/10 kt. The tropical storm is expected to continue eastward
and southeastward for the next day or so along the northern
periphery of a mid-level ridge. Early next week, Tammy and its
remnants are forecast to make a gradual turn toward the
south and southwest before dissipating. The new NHC forecast is
slightly faster than the prior advisory and represents a blend of
consensus aids HCCA and TVCN with the prior NHC forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 28/1500Z 33.3N 58.7W 45 KT 50 MPH
12H 29/0000Z 33.1N 56.4W 40 KT 45 MPH
24H 29/1200Z 32.3N 53.0W 35 KT 40 MPH
36H 30/0000Z 30.9N 50.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
48H 30/1200Z 29.2N 48.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 31/0000Z 27.8N 48.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 31/1200Z 27.1N 49.6W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 01/1200Z 27.5N 51.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 02/1200Z...DISSIPATED

$$
Forecaster Hogsett/Blake