ATL: DON - Advisories

[cycloneye]

Tropical Storm Don Discussion Number 21
NWS National Hurricane Center Miami FL AL052023
900 AM GMT Wed Jul 19 2023

Convection associated with Don remains disorganized this morning,
primarily occurring in a group of short bands in the eastern
semicircle. Satellite intensity estimates have not changed much
since the last advisory, and the initial intensity is held at 35 kt
in best agreement with the CIMSS satellite consensus.

As Don turns more westward during the next couple of days, it
should move over warmer sea surface temperatures into a somewhat
more moist air mass. This should allow some gradual strengthening,
and the new intensity forecast follows the previous forecast in
calling for a 45 kt intensity by 48 h. It should be noted that
several of the dynamical models forecast Don to get stronger than
that, possibly due to them expecting Don to move west of the
current forecast track into even warmer sea surface temperatures.
After Don turns northward later in the forecast period, it should
move north of the Gulf Stream and degenerate to a post-tropical low
over cold water between 96-120 h.

The initial motion is now 185/4 kt. Don should turn southwestward
and westward during the next 24-36 h as the subtropical ridge
builds to the northwest and north of the cyclone. This ridge
should then move eastward, leaving the cyclone in a area of
southeasterly to southerly flow on its west side. This should
allow Don to turn northward by about 72 h and then subsequently
recurve into the westerlies. The new forecast track is essentially
an update of the previous forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 19/0900Z 34.0N 39.3W 35 KT 40 MPH
12H 19/1800Z 33.7N 40.0W 35 KT 40 MPH
24H 20/0600Z 33.7N 41.2W 40 KT 45 MPH
36H 20/1800Z 34.3N 42.7W 40 KT 45 MPH
48H 21/0600Z 35.1N 44.5W 45 KT 50 MPH
60H 21/1800Z 36.4N 46.3W 45 KT 50 MPH
72H 22/0600Z 38.4N 48.2W 45 KT 50 MPH
96H 23/0600Z 43.5N 48.5W 45 KT 50 MPH
120H 24/0600Z 46.6N 43.5W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Beven

[cycloneye]

BULLETIN
Tropical Storm Don Advisory Number 22
NWS National Hurricane Center Miami FL AL052023
300 PM GMT Wed Jul 19 2023

...DON POISED TO STRENGTHEN WHILE IT MOVES OVER WARMER WATERS...


SUMMARY OF 300 PM GMT...1500 UTC...INFORMATION
----------------------------------------------
LOCATION...33.9N 39.6W
ABOUT 760 MI...1220 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...WSW OR 255 DEGREES AT 5 MPH...7 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES



Tropical Storm Don Discussion Number 22
NWS National Hurricane Center Miami FL AL052023
300 PM GMT Wed Jul 19 2023

Don is becoming better organized this morning. Satellite images
indicate deep convection is wrapping closer to the center, with
good banding features noted in the southern semicircle.
Additionally, it looks like a smaller core is forming within the
larger circulation on a 1156 UTC GMI pass, which could help
insulate the system from environmental dry air. The initial wind
speed remains 35 kt in concert with the latest TAFB Dvorak and
CIMSS ADT estimates.

The stage is finally set for intensification of Don with the
smaller core forming, along with the storm reaching a maximum in
SST during the next day or so and encountering light shear.
Gradual strengthening is shown through tomorrow, consistent with
the latest guidance and a bit higher the last NHC forecast. By
late Thursday, water temperatures begin to cool again, and shear is
forecast to increase slightly. This is probably enough to arrest
significant strengthening across the remainder of the forecast
period, so the intensity forecast is leveled off through 96 h.
Interestingly, the guidance has decreased since the last cycle, and
the model consensus is now within 5 kt of NHC at every time period.
Weakening should commence after it moves north of the Gulf Stream,
and the cyclone should become post-tropical sometime on Sunday.

Don has turned west-southwestward, still at about 4 kt. No
significant changes were made to the last NHC forecast track as Don
continues its anticyclonic loop around a blocking ridge in the
north-central Atlantic. Similar to yesterday, the ECMWF-based
guidance is on the right side of the envelope and the GFS-based
models are on the left side. The latest corrected-consensus models
are very close to the last NHC forecast track reasoning, so this
forecast is essentially just an update of the previous one.


FORECAST POSITIONS AND MAX WINDS

INIT 19/1500Z 33.9N 39.6W 35 KT 40 MPH
12H 20/0000Z 33.7N 40.4W 40 KT 45 MPH
24H 20/1200Z 33.9N 41.8W 45 KT 50 MPH
36H 21/0000Z 34.6N 43.3W 45 KT 50 MPH
48H 21/1200Z 35.7N 45.2W 45 KT 50 MPH
60H 22/0000Z 37.2N 46.9W 45 KT 50 MPH
72H 22/1200Z 39.2N 48.4W 45 KT 50 MPH
96H 23/1200Z 44.0N 47.5W 45 KT 50 MPH
120H 24/1200Z 47.0N 43.0W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Blake

[cycloneye]

Tropical Storm Don Discussion Number 23
NWS National Hurricane Center Miami FL AL052023
900 PM GMT Wed Jul 19 2023

Don has continued to become better organized during the day, with a
deep convective band now curving more than halfway around the
center, and an expanding outflow pattern especially southeast of
the storm. While the western side of the circulation still has a
lot of dry air lurking, it seems like the lack of shear is allowing
the core of the cyclone to develop. Dvorak estimates have
increased, and a blend of the latest data gives an initial wind
speed of 40 kt. Scatterometer has missed the core for about the
past day, so hopefully tonight's passes will validate the improving
satellite presentation.

Further intensification is likely for the next day or so while Don
moves over a local maximum in sea-surface temperatures (SSTs) with
light shear. Thereafter, the environment becomes less conducive
with cooling SSTs, drier environmental air, and perhaps an increase
in shear. The forecast is kept steady through the end of the work
week, then some weakening while Don crosses its own cool wake. The
NHC wind speed prediction is bumped up from the last one, consistent
with the latest model consensus, and most of the guidance is in
pretty good agreement on this scenario. The storm should lose all
of its deep convection and become post-tropical late Sunday or on
Monday after it crosses north of the Gulf Stream.

Don has turned westward, now moving a bit faster at 7 kt. The
system should turn west-northwestward tomorrow as it moves beneath a
large blocking ridge over the north-central Atlantic, with no
changes to the forecast in the short term. However, there has been
a pretty significant synoptic pattern shift in the models by Friday
with the blocking ridge much slower to depart, resulting in Don
moving more to the northwest and not accelerating as quickly
northeastward. The new forecast follows the guidance trend, but for
continuity concerns, the forecast is still faster than most of the
guidance, and further changes will likely be required on the next
advisory.


FORECAST POSITIONS AND MAX WINDS

INIT 19/2100Z 33.8N 40.3W 40 KT 45 MPH
12H 20/0600Z 33.7N 41.3W 45 KT 50 MPH
24H 20/1800Z 34.1N 42.7W 50 KT 60 MPH
36H 21/0600Z 34.8N 44.3W 50 KT 60 MPH
48H 21/1800Z 35.9N 46.1W 50 KT 60 MPH
60H 22/0600Z 37.2N 47.6W 45 KT 50 MPH
72H 22/1800Z 39.0N 48.6W 45 KT 50 MPH
96H 23/1800Z 43.0N 48.0W 45 KT 50 MPH
120H 24/1800Z 45.5N 44.0W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Blake

[cycloneye]

BULLETIN
Tropical Storm Don Advisory Number 24
NWS National Hurricane Center Miami FL AL052023
300 AM GMT Thu Jul 20 2023

...DON CONTINUES TO STRENGTHEN OVER THE CENTRAL ATLANTIC...


SUMMARY OF 300 AM GMT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...33.9N 40.9W
ABOUT 825 MI...1330 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES




Tropical Storm Don Discussion Number 24
NWS National Hurricane Center Miami FL AL052023
300 AM GMT Thu Jul 20 2023

Don continues to maintain a compact area of deep convection, with
cold cloud tops between -60 to -65C attempting to rotate
cyclonically into the northern semicircle of the
storm's circulation. An earlier ASCAT-B pass clipped Don's east
side with a peak wind-retrieval of 39 kt, but this pass might
have missed higher winds closer to the center. In fact, a Synthetic
Aperture Radar (SAR) pass that became available after the prior
advisory suggests Don's radius of maximum wind has contracted to
near 20 n mi with a peak value of 49 kt, but this derived wind
may have been contaminated by ice-scattering noted in microwave
imagery. The most recent subjective Dvorak intensity estimate was
T3.0/45-kt from TAFB, and the most recent objective intensity
estimate from SATCON was 46 kt. A blend of these various data
sources supports increasing Don's intensity to 45 kt this advisory.

There is still a window for Don to intensify more over the next 24 h
while it remains over 25-26 C sea-surface temperatures (SSTs) and
low shear helps ongoing convection moisten up the nearby environment
in a compact area. Beyond that time, SSTs decrease markedly along
Don's track, related to the storm crossing its own cold wake. In
addition, both the GFS- and ECMWF-based SHIPS guidance show
environmental mid-level relative humidity dropping below 40 percent,
and Don's small core could become sensitive to any increase in
shear, which could introduce drier air from the northeast. The most
recent regional hurricane model simulations illustrate this possible
scenario, with convection becoming sheared off to the southwest as
dry air infiltrates the storm's core in 48-60 h. Thus, the NHC
intensity forecast continues to show a peak intensity of 50 kt, with
Don beginning to weaken after 48 h. This NHC forecast is near the
latest ICVN and HCCA consensus aids. The hurricane-regional guidance
also suggests Don should become devoid of convection when it moves
north of the Gulf Stream by 96 h, and the latest forecast now shows
the system becoming post-tropical at that time.

The tropical storm continues to move westward tonight, estimated at
270/5 kt. Don should soon begin to gain latitude again as a
prominent mid-level ridge becomes centered to its northeast. As
mentioned in the previous discussion, the model trends have been
for this blocking ridge to be slow to move completely out of Don's
way, and the storm is forecast to only slowly recurve into the
higher latitudes as a result. The track guidance this cycle has
shifted a bit westward compared to the previous forecast, notably
with the 18z ECMWF coming in farther west. The NHC track forecast
has also been shifted a little westward, but not as far west as the
TVCN and HCCA consensus aids, and further adjustments may be
necessary in subsequent advisories.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0300Z 33.9N 40.9W 45 KT 50 MPH
12H 20/1200Z 34.0N 42.0W 50 KT 60 MPH
24H 21/0000Z 34.5N 43.6W 50 KT 60 MPH
36H 21/1200Z 35.3N 45.4W 50 KT 60 MPH
48H 22/0000Z 36.6N 47.1W 50 KT 60 MPH
60H 22/1200Z 38.3N 48.6W 45 KT 50 MPH
72H 23/0000Z 40.2N 49.3W 45 KT 50 MPH
96H 24/0000Z 43.9N 47.8W 40 KT 45 MPH...POST-TROPICAL
120H 25/0000Z 45.6N 42.5W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Papin

[cycloneye]

Tropical Storm Don Discussion Number 25
NWS National Hurricane Center Miami FL AL052023
900 AM GMT Thu Jul 20 2023

Deep convection associated with Don has become a little better
organized since the last advisory, with a curved convective band
currently developing near and to the north of the center. However,
the various subjective and objective satellite intensity estimates
have not changed significantly, and thus the initial intensity
remains 45 kt.

Conditions appear favorable for some strengthening during the next
18-24 h, and the intensity forecast follows the previous forecast
in bringing the winds up to 50 kt during this time. After 24 h,
the cyclone will be moving over cooler sea surface temperatures,
and after 72 h the cyclone should move north of the Gulf Stream
into an area where the water temperatures are below 20C. Based on
this and forecast dry air entrainment, the new intensity forecast
follows the previous forecast in showing Don starting to weaken
around 48 h, then it shows a faster rate of weakening after 72 h.
The cyclone is forecast to degenerate to a post-tropical low with
no convection by 96 h.

The initial motion is now 285/6 kt. A low to mid-level ridge is
forecast to build north and east of Don during the next 72 h, which
should steer the cyclone west-northwestward, northwestward, and
eventually northward during the next 72 h. The guidance has
shifted a little more westward after 48 h, and thus the 60 and 72 h
forecast are a bit to the west of the previous track, However these
points lie to the east of the various consensus models, and some
additional adjustments may be needed on subsequent advisories.
After 72 h, Don is forecast to recurve northeastward along the
southern edge of the mid-latitude westerlies.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0900Z 34.1N 41.6W 45 KT 50 MPH
12H 20/1800Z 34.4N 42.7W 50 KT 60 MPH
24H 21/0600Z 35.0N 44.4W 50 KT 60 MPH
36H 21/1800Z 36.1N 46.3W 50 KT 60 MPH
48H 22/0600Z 37.7N 48.0W 50 KT 60 MPH
60H 22/1800Z 39.3N 49.2W 45 KT 50 MPH
72H 23/0600Z 41.3N 49.7W 45 KT 50 MPH
96H 24/0600Z 45.0N 47.0W 35 KT 40 MPH...POST-TROPICAL
120H 25/0600Z 47.0N 40.0W 30 KT 35 MPH...POST-TROPICAL

$$
Forecaster Beven

[cycloneye]

Tropical Storm Don Discussion Number 26
NWS National Hurricane Center Miami FL AL052023
300 PM GMT Thu Jul 20 2023

Don has not intensified this morning, as a curved convective band
north of the center has begun to weaken. However, visible
satellite imagery and a recent scatterometer pass indicate that
the storm remains well-organized around a clear circulation center.
Subjective and objective satellite intensity estimates continue to
support an initial intensity of 45 kt, which is unchanged from the
prior advisory. However, this may be a bit generous based on the
late-arriving scatterometer pass.

The initial motion is now 290/7 kt. Don is expected to turn to
the northwest and then northward during the next 72 h, associated
with a low to mid-level ridge that is forecast to build north and
east of the forecast track. The guidance has continued to shift
westward after 36 h, and the forecast track after 48 h is thus
shifted slightly west of the previous forecast. The forecast track
represents a blend of the consensus aids and the prior forecast.
After 72 h, Don is forecast to recurve northeastward and north of
the mid-level ridge.

Conditions continue to appear favorable for some strengthening
during the next day or so, and the intensity forecast continues to
indicate an increase in intensity to 50 kt during early portion of
the forecast period. After 24 h, as Don begins to traverse cooler
sea surface temperatures, the cyclone is forecast to cross its
prior track and begin a weakening trend. By 96 h, Don is forecast
to degenerate into a post-tropical low and dissipate by 120 h.


FORECAST POSITIONS AND MAX WINDS

INIT 20/1500Z 34.4N 42.7W 45 KT 50 MPH
12H 21/0000Z 34.9N 43.8W 50 KT 60 MPH
24H 21/1200Z 35.7N 45.7W 50 KT 60 MPH
36H 22/0000Z 37.0N 47.7W 45 KT 50 MPH
48H 22/1200Z 38.6N 49.1W 45 KT 50 MPH
60H 23/0000Z 40.8N 50.2W 40 KT 45 MPH
72H 23/1200Z 42.8N 50.3W 40 KT 45 MPH
96H 24/1200Z 46.7N 46.1W 30 KT 35 MPH...POST-TROPICAL
120H 25/1200Z...DISSIPATED

$$
Forecaster Hogsett/Brown

[cycloneye]

Tropical Storm Don Discussion Number 27
NWS National Hurricane Center Miami FL AL052023
900 PM GMT Thu Jul 20 2023

A band of deep convection has developed over the eastern portion of
Don's circulation since the previous advisory, however, there has
been little overall change in the cyclone's organization today.
The latest subjective Dvorak CI numbers from SAB and TAFB were
unchanged from this morning so the initial intensity remains 45 kt.
Although that could be a little generous based on the earlier
scatterometer data, it is best to hold the intensity steady until
the next ASCAT overpass this evening.

Recent satellite fixes indicate that Don continues to move
west-northwestward (290 degrees) but at a slightly faster forward
speed of 9 kt. A strong low- to mid-level ridge that is currently
located to the north of Don is forecast to shift eastward during
the next 2 to 3 days. This should cause Don to turn northwestward
on Friday and then northward ahead of a broad mid-level trough over
the western Atlantic later this weekend. After that time, the
cyclone is forecast to turn northeastward in the low- to mid-level
southwesterly flow ahead of the aforementioned trough. The
dynamical model envelope has again shifted to the west and the NHC
track forecast has been adjusted accordingly.

Marginal sea surface temperatures, moderate shear, and nearby dry
mid-level have prevented additional strengthening today. Those
conditions are not forecast to change much during the next couple of
days and therefore, little overall change in strength is expected
during that period. Don is forecast to move north of the Gulf
stream and over much cooler waters in 60 to 72 hours, and it is
likely to become post-tropical shortly thereafter. The global
models show the system becoming an open trough in 4 to 5 days and
the official forecast calls for dissipation by that time.


FORECAST POSITIONS AND MAX WINDS

INIT 20/2100Z 34.7N 43.7W 45 KT 50 MPH
12H 21/0600Z 35.1N 45.1W 45 KT 50 MPH
24H 21/1800Z 36.2N 47.1W 45 KT 50 MPH
36H 22/0600Z 37.8N 49.0W 45 KT 50 MPH
48H 22/1800Z 39.7N 50.4W 45 KT 50 MPH
60H 23/0600Z 42.1N 51.2W 40 KT 45 MPH
72H 23/1800Z 44.6N 50.4W 35 KT 40 MPH
96H 24/1800Z 49.7N 42.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 25/1800Z...DISSIPATED

$$
Forecaster Brown

[cycloneye]

Tropical Storm Don Discussion Number 28
NWS National Hurricane Center Miami FL AL052023
300 AM GMT Fri Jul 21 2023

The band of convection noted on the eastern side of Don during the
previous advisory has wrapped around to the western side of the
tropical cyclone tonight. However, Don still is struggling to mix
out the dry air that earlier disrupted its convective structure.
ASCAT-C at 2339 UTC and ASCAT-B at 0026 UTC nicely captured Don's
circulation, and both had a peak wind retrieval of 40 kt, a bit
higher than earlier. However, there have been no changes to the
subjective Dvorak CI numbers from TAFB and SAB this cycle and so the
initial intensity remains 45 kt for this advisory.

Don continues to move west-northwestward at 290/8 kt. The storm is
being steered by a strong low- to mid-level ridge that should
gradually first shift northeastward and then eastward of the cyclone
as a short-wave trough currently over the Great Lakes ejects
eastward into the Canadian Maritimes over the next few days. This
synoptic pattern should result in Don turning to the northwest and
then north over the next 36-48 hours. Afterwards, Don should
complete recurvature northeast into the higher latitudes as it opens
up into a trough. The track guidance consensus has stabilized not
too far off from the prior forecast track, and very few adjustments
were needed to the official NHC track for this forecast cycle.

Don's structure appears quite healthy in the low-levels, per earlier
37 GHz microwave imagery which showed evidence of a closed cyan
ring. However, the combination of dry mid-level air and marginal
(24-25 C) sea surface temperatures appear to be keeping deep
convection (below -50C) in check while it attempts to wrap around
the center. These factors are likely to limit intensification, and
little change in strength is forecast over the next 36 h or so.
Weakening is then forecast to begin by 48 h as Don approaches the
north wall of the Gulf Stream and encounters a more hostile
upper-level flow pattern. Most of the global and regional-hurricane
model guidance show Don ceasing to produce organized convection by
72 h, and the storm is forecast to become post-tropical at that
time, followed by dissipation in 96 h. This forecast is in good
agreement with the consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 21/0300Z 34.8N 44.7W 45 KT 50 MPH
12H 21/1200Z 35.4N 46.1W 45 KT 50 MPH
24H 22/0000Z 36.9N 48.1W 45 KT 50 MPH
36H 22/1200Z 38.8N 49.9W 45 KT 50 MPH
48H 23/0000Z 41.1N 50.9W 40 KT 45 MPH
60H 23/1200Z 43.6N 51.1W 35 KT 40 MPH
72H 24/0000Z 46.2N 49.6W 30 KT 35 MPH...POST-TROPICAL
96H 25/0000Z...DISSIPATED

$$
Forecaster Papin

[cycloneye]

Tropical Storm Don Discussion Number 29
NWS National Hurricane Center Miami FL AL052023
500 AM AST Fri Jul 21 2023

Don has changed little in appearance during the past few hours. A
band of convection has rotated around to the southern and eastern
portions of the circulation. Microwave imagery indicates the
storm still has a well-defined low- to mid-level center. The latest
subjective satellite intensity estimates from TAFB and SAB are
unchanged from the previous advisory. Therefore, the initial
intensity remains at 45 kt.

The cyclone is moving west-northwestward at 8 kt around the southern
periphery of a strong low- to mid-level ridge. Model guidance
indicates that the ridge will build to the north and east which is
expected to turn Don to the northwest and then northward in the next
couple of days. By day 3, the cyclone is predicted to turn
northeastward in the low-level southwesterly flow ahead of a trough
forecast to be over the western Atlantic. Minor adjustments have
been made to the NHC track forecast and it remains close to the
model consensus aids.

Marginal atmospheric and oceanic conditions appear to be preventing
Don from strengthening. These conditions are not expected to change
much in the next day or so, and therefore the storm's intensity is
predicted to remain relatively steady. Don should begin to weaken
in about 36 h when it moves to the north over cooler waters and into
an environment with stronger deep-layer shear. The NHC intensity
prediction is unchanged from the previous advisory and still shows
Don becoming a remnant low by 72 h and dissipated by 96 h.


FORECAST POSITIONS AND MAX WINDS

INIT 21/0900Z 35.4N 45.6W 45 KT 50 MPH
12H 21/1800Z 36.3N 47.0W 45 KT 50 MPH
24H 22/0600Z 38.0N 49.0W 45 KT 50 MPH
36H 22/1800Z 40.0N 50.5W 45 KT 50 MPH
48H 23/0600Z 42.4N 50.9W 40 KT 45 MPH
60H 23/1800Z 45.1N 50.3W 35 KT 40 MPH
72H 24/0600Z 47.5N 49.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 25/0600Z...DISSIPATED

$$
Forecaster Bucci

[cycloneye]

Tropical Storm Don Discussion Number 30
NWS National Hurricane Center Miami FL AL052023
1100 AM AST Fri Jul 21 2023

Shortly after the release of the previous advisory convection
nearly wrapped completely around the center of Don. Since the
time, the convection has become somewhat more fragmented, but there
is still a well-defined curved band that wraps about three-quarters
of the way around Don's center. Subjective Dvorak T-numbers from
SAB and TAFB are a unanimous T3.0 or 45 kt, so the initial
intensity remains 45 kt for this advisory. A recently arriving
scatterometer overpass missed the core of the cyclone so there is
no information on the system's strength from that data source
this morning.

The initial motion estimate is still west-northwestward or 300
degrees at 9 kt. A low- to mid-level ridge to the north-northeast
of the cyclone is forecast to shift eastward during the next 24 to
36 hours causing Don to turn northwestward, and then northward
during the next day or two. After that time, Don is expected to
turn northeastward within low- to mid-level southwesterly flow
between the ridge and a broad trough over eastern Canada and the
northeastern United States. The dynamical models are tightly
clustered and little overall change was made to the previous NHC
track forecast.

Don remains over marginally warm sea surface temperatures and
within a relatively dry mid-level environment so little overall
change in strength is predicted during the next 12 to 24 hours.
The system is forecast to pass over the slightly warm waters of
the Gulf stream on Saturday, but this is not likely to result in a
significant change in strength. By Sunday morning, Don will have
moved north of the Gulf stream and over much colder SSTs. This
should result in weakening and the system's transition into a
post-tropical cyclone. Dissipation is predicted by the global
models in a little more than 3 days, and the official forecast
follows suit.

FORECAST POSITIONS AND MAX WINDS

INIT 21/1500Z 35.8N 46.5W 45 KT 50 MPH
12H 22/0000Z 36.9N 48.0W 45 KT 50 MPH
24H 22/1200Z 38.8N 49.9W 45 KT 50 MPH
36H 23/0000Z 41.1N 50.9W 45 KT 50 MPH
48H 23/1200Z 43.7N 50.6W 40 KT 45 MPH
60H 24/0000Z 46.1N 49.1W 35 KT 40 MPH...POST-TROPICAL
72H 24/1200Z 48.4N 45.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 25/1200Z...DISSIPATED

$$
Forecaster Brown

[cycloneye]

Tropical Storm Don Discussion Number 31
NWS National Hurricane Center Miami FL AL052023
500 PM AST Fri Jul 21 2023

There has been a continued increase in banding in association
with Don today. In visible satellite imagery, the primary
convective band wraps nearly completely around the center, however
the cloud tops have warmed over the northwestern portion of the
storm recently. A late arriving ASCAT-C overpass that caught the
northwestern portion of Don this morning revealed peak winds in the
43-45 kt range. Given the typical undersampling of that instrument
and the fact that it missed the potentially stronger northeastern
quadrant of the cyclone, the initial intensity has been increased
to 50 kt, which is a little above the latest subject Dvorak wind
speed estimates.

Despite the slightly stronger initial intensity, the overall
intensity forecast philosophy has not changed much. Don will be
moving over the slightly warmer waters of the Gulf stream later
tonight and Saturday which could result in some slight
strengthening. The official forecast allows for this possibility
and is close to the various intensity consensus aids through 24
hours. By early Sunday, Don is forecast to move north of the Gulf
stream and over much colder SSTs, which should cause steady
weakening. Simulated satellite imagery from the global models
suggest that Don will struggle to produce deep convection by late
Sunday, marking the system's transition to a post-tropical cyclone.
Dissipation is predicted just after 72 hours.

The storm has made its anticipated northwestward turn. A mid-level
ridge to the north-northeast of Don is expected to shift eastward
during the next day or so and allow the cyclone to turn northward
on Saturday. After that time, Don is forecast to turn northeastward
within low- to mid-level southwesterly flow between the ridge and a
broad trough over eastern Canada. The dynamical model envelope
made a noticeable eastward shift at 36 hours and beyond, which
required an eastward adjustment to the NHC track forecast. The new
track lies along the western edge of the guidance envelope and is
not as fast east as the multi-model consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT 21/2100Z 36.6N 47.5W 50 KT 60 MPH
12H 22/0600Z 37.9N 48.9W 55 KT 65 MPH
24H 22/1800Z 40.0N 50.2W 55 KT 65 MPH
36H 23/0600Z 42.4N 50.0W 50 KT 60 MPH
48H 23/1800Z 44.6N 48.6W 40 KT 45 MPH...POST-TROPICAL
60H 24/0600Z 47.1N 45.1W 35 KT 40 MPH...POST-TROPICAL
72H 24/1800Z 48.7N 41.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 25/1800Z...DISSIPATED

$$
Forecaster Brown

[cycloneye]

Tropical Storm Don Discussion Number 32
NWS National Hurricane Center Miami FL AL052023
1100 PM AST Fri Jul 21 2023

Don has generally changed little during the past several hours.
Deep convection remains fairly well organized in curved bands that
wrap around the southern half of the circulation. The initial
intensity of 50 kt is based on the earlier ASCAT data and the
storm's steady nature. This value is above the latest satellite
intensity estimates and could be a little generous.

Don is moving northwestward at 12 kt and is located on the
southwestern side of a mid-level ridge situated over the
north-central Atlantic. A mid- to upper-level trough over eastern
Canada is expected to gradually slide eastward, eroding the western
portion of the ridge. This pattern change should cause Don to turn
northward on Saturday and then northeastward and eastward later in
the weekend and early next week. The NHC track forecast is a little
to the right of the previous one from 36 h to 72 h, trending toward
the latest models.

The storm could strengthen a little on Saturday while it moves over
a patch of warmer water, however, any intensification should be
short-lived. Don is expected to move over sharply cooler waters on
Sunday and into an environment of increasing vertical wind shear
early next week. These environmental conditions should cause Don to
begin weakening in about 24 hours and it will likely become a
post-tropical cyclone by late Sunday. The system should dissipate
completely in 3 or 4 days. No change was made to the previous NHC
intensity forecast and this one lies near the middle of the guidance
envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0300Z 37.4N 48.6W 50 KT 60 MPH
12H 22/1200Z 38.7N 49.8W 55 KT 65 MPH
24H 23/0000Z 41.0N 50.1W 55 KT 65 MPH
36H 23/1200Z 43.5N 48.8W 50 KT 60 MPH
48H 24/0000Z 45.6N 46.5W 40 KT 45 MPH...POST-TROPICAL
60H 24/1200Z 47.4N 42.8W 35 KT 40 MPH...POST-TROPICAL
72H 25/0000Z 48.4N 38.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 26/0000Z...DISSIPATED

$$
Forecaster Cangialosi

[cycloneye]

Tropical Storm Don Discussion Number 33
NWS National Hurricane Center Miami FL AL052023
500 AM AST Sat Jul 22 2023

Don continues to generate curved convective bands around the center,
although the overall organization has not changed much during the
past several hours. There has also been little change in the
various objective and subjective satellite intensity estimates, so
the initial intensity remains a possibly generous 50 kt.

The initial motion is 315/12 kt as Don is located on the
southwestern side of a mid-level ridge situated over the north-
central Atlantic. A mid- to upper-level trough over eastern Canada
is expected to move eastward and erode the western portion of the
ridge during the next 24-48 h. This should allow Don to turn
northward and then recurve northeastward into the westerlies. Based
on the tightly clustered track guidance, the new NHC forecast is
similar to, but a little faster than, the previous forecast.

Don could strengthen a little during the next 12 h as it passes over
the Gulf Stream. After that, the cyclone should move over much
colder water and into increasing vertical wind shear. This
combination should cause weakening, and the new intensity forecast
calls for the system to become post-tropical between 36-48 h and
degenerate into a remnant low by 60 h. The new intensity forecast
has some minor adjustments from the previous forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 22/0900Z 38.3N 49.6W 50 KT 60 MPH
12H 22/1800Z 39.9N 50.4W 55 KT 65 MPH
24H 23/0600Z 42.3N 49.8W 55 KT 65 MPH
36H 23/1800Z 44.6N 47.9W 45 KT 50 MPH
48H 24/0600Z 46.5N 44.7W 35 KT 40 MPH...POST-TROPICAL
60H 24/1800Z 47.8N 40.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 25/0600Z 48.7N 36.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 26/0600Z...DISSIPATED

$$
Forecaster Beven

[cycloneye]

Tropical Storm Don Discussion Number 34
NWS National Hurricane Center Miami FL AL052023
1100 AM AST Sat Jul 22 2023

Don's convective structure has increased in organization this
morning. A curved band has wrapped completely around the center
with a ragged eye-like feature becoming apparent during the past
couple of hours. Earlier microwave imagery also revealed this
feature, but the convection surrounding it was fragmented.
Subjective satellite estimates from SAB and TAFB were T3.5 (55 kt)
and T3.0 (45 kt) at 1200 UTC, but given the more recent increase in
organization, the initial intensity is raised to the higher end
of those estimates at 55 kt.

Don has made its anticipated northward turn. A northward motion
with some increase in forward speed is expected today as the
cyclone is steered around the western periphery of a mid-level
ridge. After that time, Don should turn north-northeastward and
then northeastward within the mid-latitude westerlies. The
dynamical model guidance remains tightly clustered, and the new NHC
track is essentially an update of the previous advisory.

Don is currently crossing the Gulf Stream with SSTs of around 26C.
Although it is not explicitly shown below, it is possible that some
slight additional strengthening occurs within the next 6-12 hours
while Don is over the slightly warmer Gulf Stream waters. After
that time, a sharp decrease in SSTs along the track of Don and
increasing vertical wind shear should cause weakening. Don is
expected to become post-tropical around the 36 hour time period
and dissipate by 72 hours.


FORECAST POSITIONS AND MAX WINDS

INIT 22/1500Z 39.1N 50.1W 55 KT 65 MPH
12H 23/0000Z 40.7N 50.0W 55 KT 65 MPH
24H 23/1200Z 43.3N 48.8W 50 KT 60 MPH
36H 24/0000Z 45.5N 46.2W 45 KT 50 MPH...POST-TROPICAL
48H 24/1200Z 46.8N 42.6W 35 KT 40 MPH...POST-TROPICAL
60H 25/0000Z 48.0N 38.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 25/1200Z...DISSIPATED

$$
Forecaster Brown

[cycloneye]

BULLETIN
Hurricane Don Advisory Number 35
NWS National Hurricane Center Miami FL AL052023
500 PM AST Sat Jul 22 2023

...DON BECOMES A HURRICANE JUST BEFORE REACHING COOLER WATERS...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...40.1N 50.0W
ABOUT 480 MI...775 KM SSE OF CAPE RACE NEWFOUNDLAND
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...N OR 5 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...988 MB...29.18 INCHES



Hurricane Don Discussion Number 35
NWS National Hurricane Center Miami FL AL052023
500 PM AST Sat Jul 22 2023

Don's cloud pattern continued to become better organized after the
release of the previous advisory with convection wrapping around an
eye in infrared imagery. Since that time, the cloud tops over the
western semicircle have warmed somewhat, but a 1648 UTC AMSR2
microwave pass showed a well-defined low- to mid-level eye with deep
convection surrounding it. Subjective Dvorak estimates at 1800 UTC
ranged from T4.0 (65 kt) from TAFB and T3.5 (55 kt) from SAB, with
objective estimates in the 60 to 63 kt range. Since subjective
estimates have yielded a T4.0 throughout much of the afternoon, the
initial intensity has been raised to 65 kt, making Don a hurricane.

Today's strengthening was the result of the storm passing over the
warmer waters of the Gulf Stream, however it will move north of
those warmer waters later this evening, and Don has likely peaked in
intensity. Weakening should begin overnight, with a faster rate of
weakening expected Sunday through Monday as Don moves over even
colder waters and the vertical wind shear increases. The cyclone is
expected to become post-tropical by Sunday night, and dissipate by
Monday night or early Tuesday.

Don is moving northward or 005 degrees at 10 kt. The cyclone is
forecast to turn northeastward late tonight as it becomes embedded
within southwesterly flow between a ridge to its east and a broad
trough over eastern Canada. A northeastward to east-northeastward
motion should then continue until the system dissipates in 2-3 days.
The track guidance is again tightly clustered and no significant
changes to the previous official forecast were required.


FORECAST POSITIONS AND MAX WINDS

INIT 22/2100Z 40.1N 50.0W 65 KT 75 MPH
12H 23/0600Z 42.0N 49.6W 60 KT 70 MPH
24H 23/1800Z 44.5N 47.6W 50 KT 60 MPH
36H 24/0600Z 46.4N 44.5W 40 KT 45 MPH...POST-TROPICAL
48H 24/1800Z 47.7N 40.4W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 25/0600Z...DISSIPATED

$$
Forecaster Brown

[cycloneye]

Hurricane Don Discussion Number 36
NWS National Hurricane Center Miami FL AL052023
1100 PM AST Sat Jul 22 2023

Don's structure on satellite imagery remains well organized for a
tropical cyclone at such a high latitude in late July. A small but
distinct eye has persisted, surrounded by moderately cold cloud
tops. However, the coldest cloud tops are beginning to erode on the
north edge of the eye, and the upper-level outflow has also become
more restricted in that direction. These factors likely indicate
that Don is starting to feel the effects of nearby cooler waters
and increased vertical wind shear that will ultimately lead to a
swift decline in intensity. For now, the latest subjective Dvorak
estimates were T4.0 (65 kt) from both SAB and TAFB, and objective
intensity estimates currently range from 53 kt to 69 kt. It is
worth noting that UW-CIMSS ADT estimates have been much lower,
apparently due to that objective technique failing to pick up on the
eye pattern seen on satellite today. Discounting that outlier, a
blend of other subjective and objective data supports an initial
intensity of 65 kt for this advisory. Don's wind radii have also
been adjusted some due to a helpful ASCAT-B pass at 2348 UTC.

Now that Don is moving north of a warm eddy in the Gulf Stream, the
cyclone should soon encounter much colder sea-surface temperatures
along its track. Thus, steady weakening is expected to begin
shortly. As Don quickly loses its deep convection, the cyclone is
forecast to become post-tropical in 36 h, with the circulation
expected to open up into a trough axis after 48 h. This forecast is
in good agreement with the global and hurricane-regional model
guidance.

Don is now moving to the north-northeast a bit faster than before at
015/12 kt. A continued turn to the northeast with a bit more
acceleration is anticipated overnight into tomorrow as Don is
embedded within southwesterly steering flow between a subtropical
ridge to its southeast and a deep-layer trough located over eastern
Canada. This pattern should persist until Don dissipates, with the
system continuing to recurve eastward over the next 48 h. The track
guidance has shifted a bit faster than the prior cycle but still
remains along a similar trajectory. Thus the NHC track forecast
remains very close to the prior track, but just a little faster.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0300Z 41.4N 49.6W 65 KT 75 MPH
12H 23/1200Z 43.3N 48.5W 55 KT 65 MPH
24H 24/0000Z 45.5N 46.0W 45 KT 50 MPH
36H 24/1200Z 47.2N 42.1W 35 KT 40 MPH...POST-TROPICAL
48H 25/0000Z 48.1N 37.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 25/1200Z...DISSIPATED

$$
Forecaster Papin

[cycloneye]

Tropical Storm Don Discussion Number 37
NWS National Hurricane Center Miami FL AL052023
500 AM AST Sun Jul 23 2023

Don is moving over much cooler water, and its structure is
rapidly deteriorating. While the latest satellite pictures still
show a well-defined center, the eyewall convection has fallen apart
and become more fragmented. Dvorak estimates are falling quickly,
and the initial wind speed is lowered to 55 kt. Don should
continue to rapidly weaken as it moves over very cool waters with
increasing shear, and it should lose any remaining deep convection
within 24 hours and become a post-tropical cyclone. The new
forecast is lower than the previous one, closest to the GFS model.

The storm continues moving north-northeast, now at 14 kt. Don
should move faster to the northeast today and east-northeast on
Monday due steering flow mostly around the northern side of
the subtropical ridge. Guidance is tightly packed around the
previous forecast, and little change was made for this advisory,
except to move up dissipation 12 hours based on the global model
fields.

If you were thinking Don has been around a while considering the
time of year, you'd be right. The storm is moving up the list of
longest-lasting tropical cyclones on record for July (including
subtropical stages). Preliminarily, Don is tied for 10th, and the
cyclone could make the top 5 longest-lasting for July if it lasts
through early Monday.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 42.6N 48.9W 55 KT 65 MPH
12H 23/1800Z 44.5N 47.5W 45 KT 50 MPH
24H 24/0600Z 46.4N 44.2W 35 KT 40 MPH...POST-TROPICAL
36H 24/1800Z 47.5N 39.5W 30 KT 35 MPH...POST-TROPICAL
48H 25/0600Z...DISSIPATED

$$
Forecaster Blake

[cycloneye]

Tropical Storm Don Discussion Number 38
NWS National Hurricane Center Miami FL AL052023
1100 AM AST Sun Jul 23 2023

Tropical Storm Don continues to move north-northeast over cooling
sea surface temperatures. Visible and infrared satellite imagery
still show a well-defined center, with a convective band mainly
concentrated on the northern and eastern side of the system. The
subjective Dvorak satellite estimates for this advisory were steady
from TAFB at T3.5/55 kt, with SAB coming in a little lower. Given
that there is still a well-defined center, and the aforementioned
convective band, the initial intensity for this advisory remains
at 55 kt.

Don should begin to rapidly weaken as it moves over very cool
waters with increasing vertical wind shear. Simulated satellite
imagery from both the GFS and ECMWF models suggest that it should
lose any remaining deep convection within 24 hours and become a
post-tropical cyclone. The intensity forecast remains similar to
the previous forecast, with Don dissipating in 48 hours.

The system is moving north-northeast, at 14 kt. Don will
begin to increase forward speed to the northeast later today and
east-northeast tomorrow due to the steering flow around the
northern side of the subtropical ridge. Guidance remains tightly
clustered around the previous forecast, and there were very little
changes made this advisory.

The storm is moving up the list of longest-lasting tropical cyclones
on record for July (including subtropical stages). Preliminarily,
Don is tied for 10th, and the cyclone could make the top 5
longest-lasting for July if it lasts through early Monday.


FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 43.9N 47.8W 55 KT 65 MPH
12H 24/0000Z 45.5N 45.8W 45 KT 50 MPH
24H 24/1200Z 47.1N 42.0W 35 KT 40 MPH...POST-TROPICAL
36H 25/0000Z 48.3N 37.5W 30 KT 35 MPH...POST-TROPICAL
48H 25/1200Z...DISSIPATED

$$
Forecaster Kelly/Pasch

[cycloneye]

Tropical Storm Don Discussion Number 39
NWS National Hurricane Center Miami FL AL052023
500 PM AST Sun Jul 23 2023

Tropical Storm Don is moving northeastward this afternoon over the
North Atlantic's cooler sea surface temperatures, and deep
convection is starting to wane. The convective band from earlier
this morning has become more fragmented and not as well defined.
Visible satellite and a microwave AMSR2 pass earlier however, still
showed that Don has a compact low-level center, and a scatterometer
ASCAT-B pass showed winds of 48-50 kt in the southeast quadrant.
Subjective Dvorak estimates from TAFB and SAB have also started to
trend downward with this advisory cycle. Given the ASCAT-B pass and
the subjective satellite estimates, the initial intensity for this
advisory is lowered to 50 kt.

Don is starting to lose its overall convective pattern and should
begin to rapidly weaken tonight and tomorrow. Available global
model guidance suggest that Don should lose any remaining deep
convection within the next 18 to 24 hours and become a post-tropical
cyclone at that time. The intensity forecast remains similar to
the previous forecast, with Don dissipating in about 48 hours.

The system is moving to the northeast at 15 kt. Don will continue
to move to the northeast, with a slight increase in forward speed
the remainder of today, before turning to the east-northeast
tomorrow due to the steering flow around the northern side of the
subtropical ridge. Guidance remains tightly clustered, and there
was very little change to the forecast this cycle.

The storm is moving up the list of longest-lasting tropical cyclones
on record for July (including subtropical stages). Preliminary,
Don is tied for 10th, and the cyclone could make the top 5
longest-lasting for July if it lasts through early Monday.


FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 45.2N 46.5W 50 KT 60 MPH
12H 24/0600Z 46.6N 44.1W 40 KT 45 MPH
24H 24/1800Z 47.9N 39.8W 30 KT 35 MPH...POST-TROPICAL
36H 25/0600Z 48.8N 34.7W 30 KT 35 MPH...POST-TROPICAL
48H 25/1800Z...DISSIPATED

$$
Forecaster Kelly/Pasch

[cycloneye]

Tropical Storm Don Discussion Number 40
NWS National Hurricane Center Miami FL AL052023
300 AM GMT Mon Jul 24 2023

Don continues to slowly weaken and has lost just about all of its
deep convection due to very cool waters. An ASCAT-B pass around
00Z showed peak winds of about 40 kt, and because the instrument
can't always resolve the maximum winds in the storm, the initial
intensity is set to 45 kt. Don is well on its way to become a
post-tropical cyclone and it will likely complete the process later
today.

The storm is moving northeastward at 17 kt in the flow on the
northwest side of a subtropical ridge. A turn to the east-northeast
and then the east are expected later today and tonight while the
storm moves in generally zonal flow on the north side of the ridge.
Little change was made to the previous NHC track forecast. Don is
expected to continue to weaken due to cool waters and dry air
entrainment until it dissipates early Tuesday.

Don has been a very long-lasting tropical cyclone (including
subtropical stages) for the month of July. Preliminary,
up to this point the storm is tied for the 6th longest-lasting
system on record for the month.

FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 46.3N 44.8W 45 KT 50 MPH
12H 24/1200Z 47.4N 41.9W 35 KT 40 MPH...POST-TROPICAL
24H 25/0000Z 48.4N 37.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 25/1200Z...DISSIPATED

$$
Forecaster Cangialosi