ATL: SAM - Advisories

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ATL: SAM - Advisories

#1 Postby cycloneye » Wed Sep 22, 2021 3:54 pm

TCPAT3

BULLETIN
Tropical Depression Eighteen Advisory Number 1
NWS National Hurricane Center Miami FL AL182021
500 PM AST Wed Sep 22 2021

...ANOTHER TROPICAL DEPRESSION FORMS IN THE EASTERN ATLANTIC..
...EXPECTED TO STRENGTHEN OVER THE NEXT SEVERAL DAYS...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...10.1N 33.9W
ABOUT 2430 MI...3910 KM WNW OF
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Tropical Depression Eighteen
was located near latitude 10.1 North, longitude 33.9 West. The
depression is moving toward the west near 15 mph (24 km/h) and this
motion is expected to continue for the next day or so followed by a
gradual turn to the west-northwest by Friday.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Strengthening is forecast over the next several days. The
depression is forecast to become a tropical storm by tomorrow, and
could be near hurricane intensity by the weekend.

The estimated minimum central pressure is 1008 mb (29.77 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Papin



Tropical Depression Eighteen Discussion Number 1
NWS National Hurricane Center Miami FL AL182021
500 PM AST Wed Sep 22 2021

The tropical wave that NHC has been monitoring over the last several
days has gradually become better organized. The satellite structure
in particular is quite impressive for a tropical depression, with
both the 1800 UTC subjective Dvorak estimates from TAFB and SAB
at T2.5/35 kt. This bigger question, however, was if the system
possessed a well-defined closed earth-relative circulation. An
ASCAT-C pass from earlier this morning hinted that the circulation
was becoming better defined, with the development of westerly
low-level winds to the south of the convective shield. This westerly
low-level flow is also confirmed by atmospheric motion vectors
(AMVs) available from the GOES-16 meso domain over the system. While
the low-level circulation may still be somewhat broad, it now
appears to be well-defined enough to mark the formation of a
tropical cyclone. The initial intensity is set at 30-kt, in
agreement with peak wind retrievals of 28-30 kt by the earlier
scatterometer data.

The initial motion is estimated to be at 270/13 kt, though this is
somewhat uncertain given that the center has only recently formed.
An expansive mid-level ridge is located to the north and west of
the cyclone, which should maintain its heading toward the west,
though with a gradual gain in latitude as the system approaches
the western extent of the ridge by day 5. The track guidance is in
excellent agreement on this track evolution for the first three
days, with just a bit more spread in the guidance thereafter. The
ECMWF and its ensemble mean towards the end of the forecast is on
the left side of the guidance envelope, while the GFS and HWRF
models are currently on the right side. For the first NHC track
forecast, I have elected to stay close to the track consensus aids,
taking a blend of the HCCA and TCVN aids which are near the
middle of the guidance envelope.

The environment ahead of the tropical depression appears quite
favorable for intensification. Vertical wind shear is forecast by
both the ECWMF- and GFS-based SHIPS guidance to stay at or under 10
kt for the next 3-5 days as the storm traverses warm 28-29 C sea
surface temperatures. Most of the guidance responds to this
environment by indicating strengthening, and the NHC intensity
guidance follows suit, showing a steady increase in intensity
throughout the forecast period. While it might take a bit of time
for the formative low-level circulation to become vertically aligned
with the mid-level center, once that occurs, it is possible a period
of rapid intensification could occur during the five day forecast.
The forecast intensity by 120 hours (100 kt) is on the higher end of
the guidance envelope, but not as high as the latest HWRF or HAFS-B
forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT 22/2100Z 10.1N 33.9W 30 KT 35 MPH
12H 23/0600Z 10.1N 36.0W 35 KT 40 MPH
24H 23/1800Z 10.5N 38.6W 40 KT 45 MPH
36H 24/0600Z 11.0N 41.1W 50 KT 60 MPH
48H 24/1800Z 11.7N 43.4W 60 KT 70 MPH
60H 25/0600Z 12.4N 45.3W 70 KT 80 MPH
72H 25/1800Z 13.0N 46.8W 80 KT 90 MPH
96H 26/1800Z 14.2N 49.5W 90 KT 105 MPH
120H 27/1800Z 16.0N 52.5W 100 KT 115 MPH

$$
Forecaster Papin
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Re: ATL: EIGHTEEN - Advisories

#2 Postby cycloneye » Wed Sep 22, 2021 10:07 pm

BULLETIN
Tropical Depression Eighteen Advisory Number 2
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Wed Sep 22 2021

...TROPICAL DEPRESSION EXPECTED TO TAKE ITS TIME CROSSING THE
TROPICAL ATLANTIC...
...LOTS OF TIME TO MONITOR...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...10.2N 35.0W
ABOUT 1955 MI...3150 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Tropical Depression
Eighteen was located near latitude 10.2 North, longitude 35.0 West.
The depression is moving toward the west near 15 mph (24 km/h), and
this general motion is expected to continue through early Friday.
A slower motion toward the west-northwest is expected later on
Friday and continuing into the weekend.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Strengthening is forecast during the next few days, and the
depression could become a tropical storm on Thursday. It is then
forecast to become a hurricane over the weekend.

The estimated minimum central pressure is 1008 mb (29.77 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 500 AM AST.

$$
Forecaster Berg


Tropical Depression Eighteen Discussion Number 2
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Wed Sep 22 2021

The depression's organization has not improved since earlier this
afternoon. An analysis of the ambiguities from 0000 UTC ASCAT-B
data suggests that the surface circulation is just barely closed,
with the center still attached to the northern end of a trough.
Peak wind retrievals from the scatterometer pass were 25-30 kt, so
the initial intensity remains 30 kt.

Based on the ASCAT data, the depression appears to be moving just
north of due west, or 275/13 kt. Low- to mid-level ridging to the
north is expected to maintain the cyclone on a westward heading for
the next 36 hours, followed by a path toward the west-northwest
from day 2 through day 5. The more notable part of the forecast is
the forward speed. Global models are showing anomalously strong
500-mb ridging developing over the eastern and central Caribbean
Sea in 2 to 3 days, which is likely to block the depression's
forward progress toward the end of the forecast period. In fact,
the current NHC forecast has the system moving west-northwestward
at only 7 or 8 kt well east of the Lesser Antilles on days 3 through
5. All this means that it will probably be a few more days before
we have a better idea if and how the system might potentially
threaten areas farther west. For the 5-day forecast period, there
is a normal amount of spread among the track guidance, and the
updated NHC forecast is very close to a blend of the TVCA and HCCA
consensus aids. This solution is not too different from the
previous forecast.

Overall, an environment of low shear, warm sea surface
temperatures, and a moist, unstable atmosphere appears conducive
for strengthening. However, there is some sort of signal being
conveyed by the global models (e.g., the GFS, ECMWF, and UKMET)
whereby the cyclone's surface circulation does not really tighten
up for another 24 to 48 hours. Given the system's current
structure, this scenario seems plausible. Therefore, the updated
NHC intensity forecast shows a slower rate of strengthening during
the first 48 hours, just a bit below the intensity consensus in
deference to the global model solutions. After 48 hours, the
official forecast converges on top of the previous NHC forecast and
still brings the cyclone to hurricane, and then possibly major
hurricane, strength by the end of the forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0300Z 10.2N 35.0W 30 KT 35 MPH
12H 23/1200Z 10.4N 37.0W 30 KT 35 MPH
24H 24/0000Z 10.9N 39.6W 35 KT 40 MPH
36H 24/1200Z 11.4N 42.1W 45 KT 50 MPH
48H 25/0000Z 12.0N 44.3W 55 KT 65 MPH
60H 25/1200Z 12.6N 46.0W 70 KT 80 MPH
72H 26/0000Z 13.2N 47.5W 80 KT 90 MPH
96H 27/0000Z 14.5N 50.2W 90 KT 105 MPH
120H 28/0000Z 16.0N 53.3W 100 KT 115 MPH

$$
Forecaster Berg
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Re: ATL: EIGHTEEN - Advisories

#3 Postby cycloneye » Thu Sep 23, 2021 5:36 am

BULLETIN
Tropical Depression Eighteen Advisory Number 3
NWS National Hurricane Center Miami FL AL182021
500 AM AST Thu Sep 23 2021

...TROPICAL DEPRESSION EXPECTED TO STRENGTHEN AS IT MOVES ACROSS
THE TROPICAL CENTRAL ATLANTIC...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...10.5N 36.4W
ABOUT 1860 MI...2995 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 AM AST (0900 UTC), the center of Tropical Depression Eighteen
was located near latitude 10.5 North, longitude 36.4 West. The
depression is moving toward the west near 15 mph (24 km/h) and
this general motion is expected to continue through Friday.
A slower motion toward the west-northwest is expected Friday
night and continuing into the weekend.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Strengthening is forecast during the next few days, and the
depression could become a tropical storm later today. It is then
forecast to become a hurricane over the weekend.

The estimated minimum central pressure is 1008 mb (29.77 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.

$$
Forecaster Cangialosi


Tropical Depression Eighteen Discussion Number 3
NWS National Hurricane Center Miami FL AL182021
500 AM AST Thu Sep 23 2021

Satellite images indicate that the tropical depression has been
more or less steady in strength overnight. Curved bands remain
most organized to the north and west of the center with some dry
air wrapping into the eastern half of the circulation. The initial
intensity is held at 30 kt as a compromise between the earlier
ASCAT data that showed peak winds around 25 kt and 2.5/35 kt Dvorak
classifications from TAFB and SAB.

The initial motion is estimated to be 280/13 kt. The cyclone is
located on the south side of a mid-level ridge, and that should
continue to steer the system westward but at a slightly slower pace
during the next couple of days. After that time, the ridge is
expected to weaken and shift eastward. In response, the depression
is forecast to turn west-northwestward to northwestward and slow
down some more. The new NHC track forecast is largely an update of
the previous one and lies near the middle of the guidance envelope,
near the consensus aids. This forecast is also between the GFS
model on the north side of the guidance and the ECMWF on the south
side.

Environmental conditions all seem to be favorable for the storm to
gain strength during the next several days. The cyclone is expected
to traverse warm 28 deg C waters and move in an environment of low
wind shear (less than 10 kt) and fairly high moisture. Nearly all
of the models respond by showing steady strengthening during the
next several days, and so does the official forecast. This
prediction lies near the IVCN and HCCA aids, which are usually the
most skillful. The official forecast shows the system becoming a
tropical storm later today, a hurricane in a couple of days, and a
major hurricane by the end of the forecast period. In fact, some of
the models suggest that the storm could get even stronger than
currently forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 23/0900Z 10.5N 36.4W 30 KT 35 MPH
12H 23/1800Z 10.8N 38.4W 35 KT 40 MPH
24H 24/0600Z 11.3N 40.9W 40 KT 45 MPH
36H 24/1800Z 11.9N 43.3W 50 KT 60 MPH
48H 25/0600Z 12.5N 45.2W 60 KT 70 MPH
60H 25/1800Z 13.0N 46.9W 70 KT 80 MPH
72H 26/0600Z 13.7N 48.3W 80 KT 90 MPH
96H 27/0600Z 15.0N 50.8W 90 KT 105 MPH
120H 28/0600Z 16.9N 53.9W 100 KT 115 MPH

$$
Forecaster Cangialosi
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Re: ATL: SAM - Advisories

#4 Postby cycloneye » Thu Sep 23, 2021 10:01 am

BULLETIN
Tropical Storm Sam Advisory Number 4
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Thu Sep 23 2021

...DEPRESSION STRENGTHENS INTO TROPICAL STORM SAM, THE 18TH NAMED
STORM OF THE SEASON...
...NOW FORECAST TO BECOME A HURRICANE TOMORROW...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...10.9N 38.1W
ABOUT 1745 MI...2805 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Tropical Storm Sam was
located near latitude 10.9 North, longitude 38.1 West. Sam is moving
toward the west near 16 mph (26 km/h) and this general motion is
expected to continue over the next several days, but with a gradual
slowdown in forward motion.

Recent sallite wind data indicates maximum sustained winds have
increased to near 50 mph (85 km/h) with higher gusts. Additional
strengthening is forecast over the next several days, and Sam is now
forecast to become a hurricane tomorrow and be near major hurricane
intensity by the end of the weekend.

Tropical-storm-force winds extend outward up to 45 miles (75 km)
from the center.

The estimated minimum central pressure is 1003 mb (29.62 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 500 PM AST.

$$
Forecaster Papin

Tropical Storm Sam Discussion Number 4
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Thu Sep 23 2021

Overnight and this morning, the satellite structure of the tropical
cyclone has been improving, with prominent curved bands, and obvious
low-level cloud motions that indicate the circulation is becoming
established within the convection. In particular, an SSMIS microwave
pass at 0653 UTC indicated a substantial improvement in the
convective structure, with a well-defined curved band wrapping
three-quarters of the way around the center in both the 91- and
37-GHz channels. ASCAT-B wind retrievals at 1234 UTC also indicated
a tight, well-defined circulation had formed, with peak winds of
44-kt on the north side of the vortex. Subjective Dvorak satellite
intensity estimates are now T3.5/55-kt from SAB and T2.5/35-kt from
TAFB. In addition, the latest objective intensity estimates from
UW-CIMSS ADT and SATCON were at 35-kt and 43-kt respectively. Given
the recent scatterometer data, the intensity has been set to 45-kt
for this advisory. Thus, Tropical Depression 18 has been upgraded to
Tropical Storm Sam. It is noteworthy that this is the 2nd earliest
formation of the 18th named storm in the Atlantic basin, moving
ahead of the 2005 hurricane season, and only trailing last year.

Sam continues to move to the west-northwest with an estimated motion
at 280/14 kt. A prominent mid-level ridge remains entrenched to the
north of the cyclone, and this feature should continue to steer Sam
to the west-northwest over the next 2-3 days. Over this period, the
ridge orientation actually shifts more westward ahead of the cyclone
as a deep-layer trough digs in well northeast of Sam. This gradual
change in the synoptic pattern should also result in a slowdown in
Sam's forward motion over the next 72 hours. While the track
guidance remains in good agreement over this period, larger spread
begins to take shape beyond the day 3 forecast. Similar to
yesterday, the ECMWF model and its ensemble mean flanks the
southwest side of the guidance envelop, while the GFS is on the
northeast side by day 5. These differences appear to be partially
related to the mid-level ridge intensity on the western end, which
could begin to be eroded by a mid-latitude trough off the eastern
United States in 120-h. In addition, differences in both the size
and intensity of Sam may also play a role in its ultimate track
evolution. For this advisory, the latest NHC track forecast remains
close to the consensus aids TCVN and TCVE, which represents a slight
shift westward and a bit faster motion compared to the previous
forecast. Because Sam is forecast to slow down, it remains too early
to determine what impacts, direct or indirect, could be felt by the
Lesser Antilles by this cyclone.

The previously mentioned SSMIS microwave imagery also indicated that
the low-level center has become better aligned with the mid-level
vortex, perhaps a bit earlier than anticipated given the
scatterometer data from last night. This improvement in structure,
combined with favorable low vertical wind shear under 10 kt and warm
28-29 C sea-surface temperatures, argues for significant
intensification. In fact, the GFS-SHIPS rapid intensification index
now give Sam a 39 percent chance of a 65-kt increase over the next
72 hours, which is more than 7 times the climatological value. Thus,
the NHC intensity forecast has been raised quite a bit from the
prior one, especially in the short-term. The latest forecast now
makes Sam a hurricane in 36 hours, and a major hurricane in 72
hours. This intensity forecast is just a shade under the latest HCCA
consensus aid. Thereafter, a more gradual intensification rate is
forecast. By this period it is possible that Sam could undergo hard
to predict inner-core changes such as eyewall replacement cycles. In
addition, the ECMWF-SHIPS suggests that the shear may also increase
a little in days 4-5 which also argues for a bit slower rate of
intensification for this period.


FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 10.9N 38.1W 45 KT 50 MPH
12H 24/0000Z 11.3N 40.3W 50 KT 60 MPH
24H 24/1200Z 11.9N 42.9W 60 KT 70 MPH
36H 25/0000Z 12.3N 45.0W 70 KT 80 MPH
48H 25/1200Z 12.7N 46.7W 80 KT 90 MPH
60H 26/0000Z 13.2N 48.2W 90 KT 105 MPH
72H 26/1200Z 13.7N 49.4W 100 KT 115 MPH
96H 27/1200Z 15.3N 52.1W 105 KT 120 MPH
120H 28/1200Z 17.4N 55.2W 110 KT 125 MPH

$$
Forecaster Papin
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Re: ATL: SAM - Advisories

#5 Postby cycloneye » Thu Sep 23, 2021 4:01 pm

BULLETIN
Tropical Storm Sam Advisory Number 5
NWS National Hurricane Center Miami FL AL182021
500 PM AST Thu Sep 23 2021

...SAM CONTINUES TO STRENGTHEN...
...RAPID INTENSIFICATION POSSIBLE OVER THE NEXT SEVERAL DAYS...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...11.1N 39.7W
ABOUT 1635 MI...2635 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Tropical Storm Sam was
located near latitude 11.1 North, longitude 39.7 West. Sam is moving
toward the west near 16 mph (26 km/h) and a general west to
west-northwest motion is expected to continue over the next several
days, with a gradual slowdown in forward motion.

Maximum sustained winds have increased to near 60 mph (95 km/h) with
higher gusts. Rapid intensification is forecast during the next
several days. Sam is forecast to become a hurricane tomorrow morning
and could become a major hurricane by Saturday.

Tropical-storm-force winds extend outward up to 60 miles (95 km)
from the center.

The estimated minimum central pressure is 1000 mb (29.53 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Papin



Tropical Storm Sam Discussion Number 5
NWS National Hurricane Center Miami FL AL182021
500 PM AST Thu Sep 23 2021

Sam could be in the beginning stages of developing a small
inner-core this afternoon as a central dense overcast is beginning
to take shape. On geostationary visible satellite imagery, the storm
has occasionally exhibited a clear area, though this feature has
been tilted a bit southeast of the estimated low-level center
position. In addition, overshooting convective cloud tops have been
recirculating cyclonically around this feature, suggesting
convective symmetrization that may help shield the low-level vortex
from dry-air intrusion as seen earlier on the northwest side of Sam.
Unfortunately, I have not received a high resolution microwave pass
over Sam in 9-12 hours, so there remains some uncertainty on the
structure underneath the cirrus canopy. The latest subjective Dvorak
estimates from SAB and TAFB were 55-kt and 45-kt respectively.
Taking a blend of these intensity estimates yields 50-kt for this
advisory.

Sam's estimated motion is nearly identical to this morning, moving
north of due west at 280/14 kt. A large and anomalously strong
mid-level ridge is located poleward of Sam and should maintain the
current west to west-northwest heading over the next 2-3 days.
However, this ridge-axis is forecast to build in to the northwest
ahead of Sam, which is likely to gradually slow down this forward
motion over the next few days. In fact, Sam is forecast to move
unusually slow for a tropical cyclone in the deep tropics east of
the Lesser Antilles. Afterwards, a weakness in the ridge to the
northwest is forecast to gradually develop as a broad deep-layer
trough parks itself just offshore of the eastern United States by
early next week. This could potentially allow Sam to gain a bit more
latitude at a somewhat faster forward motion as the ridge axis
shifts back east. The track guidance this cycle has slowed down a
bit compared to this morning and is also a bit further south in the
early portion of the forecast. The NHC official track will follow
suit this advisory, though is not quite as slow as the GFS model. It
is interesting to note that both the GFS and ECMWF ensemble guidance
this afternoon shows a significant spread in track solutions by day
5 in the cross-track direction, so this track forecast is a bit more
uncertain than usual.

With the apparent improvement in inner-core structure inferred
on satellite today, Sam appears poised to rapidly intensify in the
short-term. In fact, the latest GFS-SHIPS guidance is now explicitly
forecasting rapid intensification over the next 24-48 hours. This
seems feasible given that the guidance is forecasting 5 kt or less
vertical wind shear over the next 60 hours as the cyclone traverses
over warm 28-29 C sea-surface temperatures. Thus, the intensity
guidance in the short-term has been raised once again, now showing a
50-kt increase in intensity over the next 48 hours taking Sam to
major hurricane intensity by Saturday afternoon. Remarkably, this
rapid intensification is still below the latest HCCA and LGEM
guidance over this time span. After this period, Sam is likely to
start undergoing inner core fluctuations, related to eyewall
replacement cycles that are challenging to forecast far in advance.
A modest increase in southwesterly vertical wind shear could also
occur in the day 3-5 period. Thus, the NHC intensity forecast still
tops off Sam as 110-kt hurricane by the end of the forecast period,
which is on the high end of the intensity guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 11.1N 39.7W 50 KT 60 MPH
12H 24/0600Z 11.5N 41.9W 60 KT 70 MPH
24H 24/1800Z 11.9N 44.2W 75 KT 85 MPH
36H 25/0600Z 12.3N 46.0W 90 KT 105 MPH
48H 25/1800Z 12.6N 47.4W 100 KT 115 MPH
60H 26/0600Z 13.1N 48.7W 105 KT 120 MPH
72H 26/1800Z 13.7N 50.0W 110 KT 125 MPH
96H 27/1800Z 15.2N 52.5W 110 KT 125 MPH
120H 28/1800Z 17.5N 55.5W 110 KT 125 MPH

$$
Forecaster Papin
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Re: ATL: SAM - Advisories

#6 Postby cycloneye » Thu Sep 23, 2021 10:05 pm

BULLETIN
Tropical Storm Sam Advisory Number 6
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Thu Sep 23 2021

...SMALL SAM RAPIDLY INTENSIFYING...
...RAPID INTENSIFICATION FORECAST TO CONTINUE THROUGH SATURDAY...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...11.2N 40.9W
ABOUT 1560 MI...2505 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...997 MB...29.44 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Tropical Storm Sam was
located near latitude 11.2 North, longitude 40.9 West. Sam is
moving toward the west near 15 mph (24 km/h), and this motion with
a decrease in forward speed is expected through Saturday. A motion
toward the west-northwest at an even slower forward speed is
expected late Saturday into Sunday.

Sam is rapidly intensifying, and maximum sustained winds have
increased to near 70 mph (110 km/h) with higher gusts. Rapid
intensification is forecast to continue through early Saturday.
Sam is likely to become a hurricane very soon and then could be a
major hurricane by Friday night or early Saturday.

Sam is a small tropical storm. Tropical-storm-force winds extend
outward up to 45 miles (75 km) from the center.

The estimated minimum central pressure is 997 mb (29.44 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 500 AM AST.

$$
Forecaster Berg




Tropical Storm Sam Discussion Number 6
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Thu Sep 23 2021

Microwave data from around the time of the previous advisory
revealed that Sam has developed a well-defined inner core, including
a nearly closed eyewall feature in the 91-GHz channel. Dvorak
estimates from TAFB and SAB have increased to T3.5 and T4.0,
respectively, and the initial intensity is therefore estimated to be
60 kt. Sam's 24-hour intensity change qualifies as rapid
intensification, since the cyclone was only a 30-kt tropical
depression at this time yesterday. Sam is small, however. Recent
scatterometer data showed that tropical-storm-force winds only
extend a maximum of 40 n mi from the center, and the radius of
maximum winds is estimated to be about 15 n mi. This small size is
likely to have implications on Sam's future intensity.

Sam is moving a little slower toward the west (280/13 kt). A
mid-tropospheric ridge is expected to build across the Caribbean
Sea and extend northeastward over the central Atlantic during the
next few days. This blocking high is expected to cause Sam to slow
down to 6 to 7 kt by late Saturday and Sunday while it maintains a
westward to west-northwestward heading. Global models suggest the
ridge may weaken and shift eastward a bit by days 4 and 5, allowing
Sam to turn to the northwest and speed up a little by the end of
the forecast period. The ECMWF, HWRF, and HCCA models lie along
the southern edge of the main pack of models, while the ECENS
ensemble mean is even farther south. The GFS and the HMON are on
the northern side. Partially due to an adjustment of the initial
position, the new NHC track forecast has been shifted southward a
bit from the previous forecast, and it lies just south of the TVCA
consensus aid--but not as far to the left as the previously
mentioned southern models.

Environmental conditions and Sam's structure and size are ideal for
continued rapid intensification (RI). The SHIPS RI index for a
30-kt increase in 24 hours is nearly 50 percent. The DTOPS
methodology, which uses inputs from the statistical-dynamical and
deterministic models, shows RI indices for various forecast periods
exceeding 90 percent. Therefore, rapid strengthening is being
forecast at least for the next 36 hours, with Sam becoming a
hurricane very soon and then a major hurricane by Friday night or
Saturday morning. One caveat to this forecast is that although
Sam's small size more readily allows for RI to occur, it can also
make the cyclone more prone to weakening if, for example, vertical
shear increases. By 48 hours, the intensity models show the
strengthening trend leveling off, and the NHC intensity forecast
follows suit. Fluctuations in intensity from days 3 through 5 are
likely, both due to normal internal dynamics within the storm and
the cyclone's response to the surrounding environment in relation
to its small size.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 11.2N 40.9W 60 KT 70 MPH
12H 24/1200Z 11.4N 42.9W 75 KT 85 MPH
24H 25/0000Z 11.8N 45.0W 90 KT 105 MPH
36H 25/1200Z 12.1N 46.6W 105 KT 120 MPH
48H 26/0000Z 12.5N 47.8W 110 KT 125 MPH
60H 26/1200Z 13.0N 49.1W 110 KT 125 MPH
72H 27/0000Z 13.5N 50.4W 110 KT 125 MPH
96H 28/0000Z 15.3N 53.2W 110 KT 125 MPH
120H 29/0000Z 17.3N 56.1W 110 KT 125 MPH

$$
Forecaster Berg
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Re: ATL: SAM - Advisories

#7 Postby cycloneye » Fri Sep 24, 2021 3:38 am

BULLETIN
Hurricane Sam Advisory Number 7
NWS National Hurricane Center Miami FL AL182021
500 AM AST Fri Sep 24 2021

...SAM IS NOW A HURRICANE...
...RAPID INTENSIFICATION FORECAST TO CONTINUE...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...11.5N 42.2W
ABOUT 1470 MI...2365 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...993 MB...29.33 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 AM AST (0900 UTC), the center of Hurricane Sam was located
near latitude 11.5 North, longitude 42.2 West. Sam is moving toward
the west near 15 mph (24 km/h) and this motion is expected to
continue through tonight. A decrease in forward speed and a motion
toward the west-northwest are expected over the weekend.

Maximum sustained winds have increased to near 75 mph (120 km/h)
with higher gusts. Rapid intensification is forecast to continue,
and Sam is likely to become a major hurricane tonight or early
Saturday.

Hurricane-force winds extend outward up to 15 miles (30 km) from the
center and tropical-storm-force winds extend outward up to 60 miles
(95 km).

The estimated minimum central pressure is 993 mb (29.33 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.

$$
Forecaster Cangialosi



Hurricane Sam Discussion Number 7
NWS National Hurricane Center Miami FL AL182021
500 AM AST Fri Sep 24 2021

Sam continues to rapidly intensify. Satellite images show a small,
but well-developed inner core and pronounced curved bands that wrap
most of the way around the center. There are some dry slots,
however, between the core and bands. The latest satellite intensity
estimates range from 55 to 77 kt, and based on that data and the
continued improvement in the cyclone's structure, the initial wind
speed is increased to 65 kt. This makes Sam a hurricane, the
seventh one of the 2021 Atlantic hurricane season. It should be
noted that Sam has a compact wind field, with hurricane-force and
tropical-storm-force winds estimated to only extend outward up to 15
and 50 n mi from the center, respectively.

Sam is moving westward at about 13 kt, and this general motion
should continue for another 12 to 24 hours as it moves in the flow
on the south side of a mid-level ridge. After that time, a decrease
in forward speed and a turn to the west-northwest are expected, and
the official forecast has Sam moving at a slow pace of only 6-8 kt
during the 48-96-hour time period. By the middle of next week, the
ridge is forecast to slide eastward as a trough moves over the
western Atlantic. In response, the hurricane will likely turn
northwestward as it approaches the northern Leeward Islands. The
models have changed little this cycle with the GFS still on the
northern side of the guidance envelope and the ECMWF on the
southern side. The NHC track forecast is essentially an update of
the previous one and lies between the GFS and ECMWF models, and near
the consensus aids.

The large scale environmental conditions all appear favorable for
continued rapid intensification during the next day or so as the
hurricane is expected to remain over warm 29 deg C waters and in
very low wind shear conditions. All of the SHIPS rapid
intensification indices are well above the climatological means, and
the NHC intensity forecast calls for Sam to become a major hurricane
by early Saturday. Beyond a couple of days, the environment is
likely to become a little less ideal, and most of the models show
Sam leveling off in strength, and so does the official forecast.
This intensity prediction lies near a blend of the FSSE, HCCA, and
IVCN consensus models. Regardless of the details, Sam is expected
to be a significant hurricane during the next several days.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 11.5N 42.2W 65 KT 75 MPH
12H 24/1800Z 11.7N 44.0W 80 KT 90 MPH
24H 25/0600Z 12.1N 45.9W 95 KT 110 MPH
36H 25/1800Z 12.5N 47.4W 105 KT 120 MPH
48H 26/0600Z 12.9N 48.7W 115 KT 130 MPH
60H 26/1800Z 13.4N 50.0W 115 KT 130 MPH
72H 27/0600Z 14.1N 51.1W 110 KT 125 MPH
96H 28/0600Z 15.9N 53.8W 110 KT 125 MPH
120H 29/0600Z 17.8N 56.6W 110 KT 125 MPH

$$
Forecaster Cangialosi
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Re: ATL: SAM - Advisories

#8 Postby cycloneye » Fri Sep 24, 2021 10:38 am

BULLETIN
Hurricane Sam Advisory Number 8
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Fri Sep 24 2021

...SAM TAKING A MOMENTARY PAUSE IN STRENGTHENING...
...RAPID INTENSIFICATION FORECAST TO RESUME SOON...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...11.8N 43.7W
ABOUT 1365 MI...2200 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...993 MB...29.33 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Hurricane Sam was located
near latitude 11.8 North, longitude 43.7 West. Sam is moving just
north of due west near 14 mph (22 km/h) and this motion is expected
to continue through tonight. A decrease in forward speed and a
motion toward the west-northwest are expected over the weekend.

Maximum sustained winds remain near 75 mph (120 km/h) with higher
gusts. Rapid intensification is forecast to resume over the next
several days and Sam is likely to become a major hurricane on
Saturday.

Hurricane-force winds extend outward up to 15 miles (30 km) from the
center and tropical-storm-force winds extend outward up to 60 miles
(95 km).

The estimated minimum central pressure is 993 mb (29.33 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 500 PM AST.

$$
Forecaster Papin



Hurricane Sam Discussion Number 8
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Fri Sep 24 2021

After rapidly intensifying from a tropical depression to a hurricane
over the past 24 hours, Sam is taking a momentary pause from
intensification. The structure on visible satellite imagery remains
quite healthy, with tightly coiled outer bands and a small but very
cold central dense overcast. However, microwave passes at 0957 UTC
and 1211 UTC on the 89-91 GHz channels show an erosion of the
inner-core structure on the west side, which could be related to the
dry-air slots mentioned in the previous advisory entraining into the
core, temporarily disrupting the structure underneath the cirrus.
The latest subjective Dvorak intensity estimates from TAFB and SAB
were T4.0/4.0-65 kt and T4.0/4.5-75 kt while the latest UW-CIMSS ADT
and SATCON objective estimates were both at 59 kt. The current
intensity is being maintained at 65 kt for this advisory, taking a
blend of these subjective and objective estimates. Sam remains a
very small tropical cyclone, with the latest scatterometer wind data
indicating that tropical-storm and hurricane-force winds have have
not expanded much from last night.

Sam continues to move just north of due west, but is beginning to
gradually slow down at 280/12 kt. Over the next 24-36 hours, Sam is
expected to maintain a general west to west-northwest heading but
will slow down gradually as the strongest mid-level ridging becomes
oriented more to the northwest of the hurricane. This ridge
repositioning is thanks in part to a strong deep-layer trough well
northeast of Sam that is digging in south of the Azores. Towards the
end of the forecast, this trough will cutoff and gradually decay,
allow the mid-level ridging to build-in back east as another
deep-layer trough becomes established just off the eastern United
States coastline. In general, the track guidance is in fairly good
agreement on this general solution. However, differences remain in
the details between how strong the ridge will be immediately to the
north of Sam at the end of the 5-day forecast. The deterministic GFS
and Canadian models show weaker ridging that erodes sooner, allowing
a bit more poleward motion, while the ECMWF has stronger ridging
that places its track on the equatorward side of the guidance
envelope. The consensus track aid TCVN blends the aforementioned
model guidance and has changed little this cycle, and the latest NHC
track forecast is largely an update of the previous advisory.

While the shear remains very low over Sam as diagnosed by the GFS-
and ECMWF-based SHIPS guidance, the 700-500 mb layer mean relative
humidity is a bit on the low side, and could possibly explain why
Sam was susceptible to the dry-air intrusion that disrupted the core
structure this morning. However, the vertical wind shear is expected
to remain very low for the next 48-60 hours, and the hurricane
should be able to easily mix out the dry air over the inner-core.
The wind field also remains very compact, so once the inner-core
closes back off, rapid intensification is expected to resume. The
latest NHC intensity forecast still shows Sam becoming a major
hurricane by tomorrow and currently has a peak intensity as a
category 4 hurricane in 48-72 hours. Thereafter, a bit more vertical
wind shear, and the likelihood of eyewall replacement cycles are
likely to lead to fluctuations in the intensity that are difficult
to predict ahead of time. The current intensity forecast remains
close to the HCCA and IVCN consensus guidance. Regardless of the
details, Sam is expected to be a significant hurricane through the
forecast period.

FORECAST POSITIONS AND MAX WINDS

INIT 24/1500Z 11.8N 43.7W 65 KT 75 MPH
12H 25/0000Z 12.0N 45.4W 75 KT 85 MPH
24H 25/1200Z 12.3N 47.1W 90 KT 105 MPH
36H 26/0000Z 12.7N 48.4W 105 KT 120 MPH
48H 26/1200Z 13.1N 49.7W 115 KT 130 MPH
60H 27/0000Z 13.7N 50.9W 115 KT 130 MPH
72H 27/1200Z 14.6N 52.1W 115 KT 130 MPH
96H 28/1200Z 16.4N 54.8W 110 KT 125 MPH
120H 29/1200Z 18.2N 57.7W 110 KT 125 MPH

$$
Forecaster Papin
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Re: ATL: SAM - Advisories

#9 Postby cycloneye » Fri Sep 24, 2021 4:06 pm

BULLETIN
Hurricane Sam Advisory Number 9
NWS National Hurricane Center Miami FL AL182021
500 PM AST Fri Sep 24 2021

...SAM'S INTENSIFICATION RESUMES AS THE HURRICANE SLOWS ITS
FORWARD MOTION...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...12.1N 44.8W
ABOUT 1290 MI...2075 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...986 MB...29.12 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Hurricane Sam was located
near latitude 12.1 North, longitude 44.8 West. Sam is moving toward
the west near 12 mph (19 km/h) and this motion is expected to
continue with a gradual decrease in forward speed and turn toward
the west-northwest over the weekend.

Maximum sustained winds have increased to near 85 mph (140 km/h)
with higher gusts. Rapid intensification is forecast over the next
several days, and Sam is expected to become a major hurricane on
Saturday.

Hurricane-force winds extend outward up to 15 miles (30 km) from the
center and tropical-storm-force winds extend outward up to 60 miles
(95 km).

The estimated minimum central pressure is 986 mb (29.12 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Papin



Hurricane Sam Discussion Number 9
NWS National Hurricane Center Miami FL AL182021
500 PM AST Fri Sep 24 2021

Sam's structure on satellite has improved this afternoon, with
overshooting cloud tops rotating quickly around the small central
dense overcast, providing the appearance that the hurricane is
mixing out the dry air that affected its core structure this
morning. In fact, the last few visible satellite images suggest that
a small eye is clearing out within the cirrus canopy. Interestingly,
a recent 1930 UTC SSMIS pass suggests concentric bands are also
forming in Sam's core structure and it remains to be seen how that
structure will affect the wind field evolution of the hurricane. The
latest subjective Dvorak intensities estimates form TAFB and SAB
were a consensus T4.5/75 kt, while the latest SATCON and ADT
estimates from UW-CIMSS have also increased this afternoon. The
current advisory intensity has been set to 75-kt. Given the
recent trends on satellite, this may be conservative.

The motion of Sam has remained on the same heading, though the
storm is beginning to slow down with the estimate now at 280/10
kt. An additional slowdown in forward motion is anticipated in the
short-term as the mid-level ridging shuffles to the northwest of
the tropical cyclone, impeding its forward motion. However, after
72 hours, this same ridge is expected to shift back to the
northeast of Sam as a deep-layer trough off the Eastern United
States coastline becomes established. Track guidance spread
increases towards the end of the forecast, with the ECMWF and GFS
remaining at odds, with the former on the equatorward side, and
the latter on the poleward side of the track envelope. The
consensus aids, however, have changed little from the previous
advisory and the latest NHC track forecast is quite similar to the
previous one.

Now that Sam appears to have mixed out the dry air seen this
morning, intensification, likely rapid, is resuming. The only fly in
the ointment is the current concentric banding structure on
microwave imagery, which hints at the possibility of an eyewall
replacement cycle. Assuming the smaller eye will not collapse in the
short term, rapid intensification appears likely over the next 12-24
hours and the intensity has been raised in the short term, taking
Sam to major hurricane intensity by tomorrow. The latest NHC
intensity forecast now shows a slightly higher peak at 120-kt in 48
hours followed by very gradual decay, due to a subtle increase in
vertical wind shear, potentially some upwelling effects due to the
slow forward notion, and eyewall replacement cycles that could lead
to a broadening of the wind field. The latest NHC intensity forecast
starts out on the high side of the intensity guidance but ends up
very close to the HCCA consensus aid by the end of the forecast
period. Regardless of the details, Sam is expected to be a
significant hurricane through the forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT 24/2100Z 12.1N 44.8W 75 KT 85 MPH
12H 25/0600Z 12.3N 46.5W 90 KT 105 MPH
24H 25/1800Z 12.7N 48.1W 105 KT 120 MPH
36H 26/0600Z 13.1N 49.3W 115 KT 130 MPH
48H 26/1800Z 13.5N 50.5W 120 KT 140 MPH
60H 27/0600Z 14.3N 51.7W 115 KT 130 MPH
72H 27/1800Z 15.1N 52.9W 115 KT 130 MPH
96H 28/1800Z 16.9N 55.1W 110 KT 125 MPH
120H 29/1800Z 18.9N 58.1W 110 KT 125 MPH

$$
Forecaster Papin
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Re: ATL: SAM - Advisories

#10 Postby cycloneye » Fri Sep 24, 2021 10:00 pm

BULLETIN
Hurricane Sam Advisory Number 10
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Fri Sep 24 2021

...SAM NOW A CATEGORY 2 HURRICANE...
...FORECAST TO BECOME A MAJOR HURRICANE ON SATURDAY...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...12.4N 45.9W
ABOUT 1215 MI...1950 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...100 MPH...155 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...982 MB...29.00 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the eye of Hurricane Sam was located
near latitude 12.4 North, longitude 45.9 West. Sam is moving toward
the west-northwest near 14 mph (22 km/h). A motion toward the west
or west-northwest with a decrease in forward speed is expected
over the weekend. A turn toward the northwest is forecast on
Monday.

Maximum sustained winds have increased to near 100 mph (155 km/h)
with higher gusts. Additional strengthening is forecast, and Sam
is expected to become a major hurricane on Saturday.

Sam is a small hurricane. Hurricane-force winds extend outward up
to 15 miles (30 km) from the center and tropical-storm-force winds
extend outward up to 60 miles (95 km).

The estimated minimum central pressure is 982 mb (29.00 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 500 AM AST.

$$
Forecaster Berg



Hurricane Sam Discussion Number 10
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Fri Sep 24 2021

Sam developed a 10-n mi wide eye in infrared satellite images a
few hours ago, surrounded by a ring of cloud tops as cold as about
-70 degrees Celsius. The core of the hurricane remains compact.
In fact, recent Synthetic Aperture Radar (SAR) data indicated that
the radius of maximum winds is only about 6 n mi. Dvorak estimates
were T5.0/90 kt from TAFB and T4.5/77 kt from SAB at 0000 UTC, and
given the additional clearing of the eye since then, Sam's intensity
is raised to 85 kt.

Sam has been moving toward the west-northwest during the past 6 to
12 hours with a motion of 285/12 kt. The track forecast reasoning
remains the same, and the model guidance is packed more tightly
than normal through day 5. A blocking ridge lying to the north and
northwest is expected to cause Sam to slow down over the weekend
and maintain a motion toward the west or west-northwest. On days 3
through 5, the ridge is expected to shift eastward, with a
deep-layer trough developing over the western Atlantic. This
should allow Sam to turn northwestward toward the end of the
forecast period. The NHC track forecast has not budged much and
remains close to the TVCA consensus aid. Based on this forecast,
and nearly all of the reliable guidance, Sam is expected to still
be well to the east or northeast of the northern Leeward Islands
through day 5.

Deep-layer shear is expected to be less than 10 kt for the next day
or two, and Sam will be heading toward waters of higher oceanic
heat content. These conditions favor continued strengthening, and
the hurricane is forecast to become a major hurricane on Saturday
and possibly reach a peak intensity in 2 to 3 days. For this
period, the NHC forecast is close to the HCCA consensus aid and
is near the high end of the guidance envelope. As is usually the
case with hurricanes this small and strong, fluctuations in
intensity due to eyewall replacement cycles will be possible. On
days 3 through 5, some increase in shear as Sam approaches the
deep-layer western Atlantic trough is possible, and modest weakening
is shown at those times.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 12.4N 45.9W 85 KT 100 MPH
12H 25/1200Z 12.7N 47.4W 100 KT 115 MPH
24H 26/0000Z 13.1N 48.8W 110 KT 125 MPH
36H 26/1200Z 13.5N 50.0W 115 KT 130 MPH
48H 27/0000Z 14.1N 51.2W 120 KT 140 MPH
60H 27/1200Z 14.8N 52.4W 120 KT 140 MPH
72H 28/0000Z 15.7N 53.5W 115 KT 130 MPH
96H 29/0000Z 17.4N 55.8W 110 KT 125 MPH
120H 30/0000Z 19.5N 58.8W 110 KT 125 MPH

$$
Forecaster Berg
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Re: ATL: SAM - Advisories

#11 Postby cycloneye » Sat Sep 25, 2021 3:40 am

BULLETIN
Hurricane Sam Advisory Number 11
NWS National Hurricane Center Miami FL AL182021
500 AM AST Sat Sep 25 2021

...SAM ALMOST A MAJOR HURRICANE...
...ADDITIONAL STRENGTHENING EXPECTED...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...12.8N 46.7W
ABOUT 1150 MI...1855 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...110 MPH...175 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 13 MPH...20 KM/H
MINIMUM CENTRAL PRESSURE...973 MB...28.74 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 AM AST (0900 UTC), the eye of Hurricane Sam was located
near latitude 12.8 North, longitude 46.7 West. Sam is moving toward
the west-northwest near 13 mph (20 km/h). A slower motion to the
west-northwest is expected over the weekend, followed by a turn to
the northwest on Monday.

Maximum sustained winds have increased to near 110 mph (175 km/h)
with higher gusts. Additional strengthening is forecast, and Sam is
expected to become a major hurricane later today.

Sam is a small hurricane. Hurricane-force winds extend outward up
to 15 miles (30 km) from the center and tropical-storm-force winds
extend outward up to 60 miles (95 km).

The estimated minimum central pressure is 973 mb (28.74 inches).


HAZARDS AFFECTING LAND
----------------------
None.


NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.

$$
Forecaster Cangialosi


Hurricane Sam Discussion Number 11
NWS National Hurricane Center Miami FL AL182021
500 AM AST Sat Sep 25 2021

Sam continues to rapidly intensify. Geostationary satellite and
microwave images show that the storm has a very small and distinct
eye surrounded by a nearly symmetric ring of cold cloud tops. The
latest Dvorak estimates range from 90 to 102 kt, and based on that
data, the initial intensity is increased to 95 kt. Although Sam
is nearly a major hurricane, it remains quite compact with
tropical-storm-force and hurricane-force winds estimated to only
extend 50 n mi and 15 n mi from the center, respectively.

The hurricane is moving west-northwestward at 11 kt and is currently
being steered by a mid-level ridge to its north. There has been
little change to the track forecast philosophy or model guidance.
Sam is expected to continue west-northwestward during the next two
or three days, but it is forecast to move at a notably slower pace
of 6-8 kt during most of that time period. After that time, the
ridge is expected to shift eastward as a deep-layer trough becomes
established over the western Atlantic. This change in the steering
pattern should cause Sam to turn northwestward and speed up some by
the middle of next week. The models are in fairly good agreement,
and the NHC track forecast is largely an update of the previous one.
Based on this forecast, and nearly all of the reliable guidance,
Sam is expected to still be well to the east or northeast of the
northern Leeward Islands through day 5.

Continued steady or rapid strengthening is expected during the next
day or two as the hurricane remains in near ideal conditions of very
low wind shear and warm 29 deg C waters. However, beyond that time
the shear is expected to increase a little, and that will likely
cause Sam to level off in strength or weaken slightly next week.
The NHC intensity forecast is slightly above the models in the short
term, given the impressive structure of the hurricane and favorable
conditions, but falls in line with the consensus aids at the longer
lead times. Regardless of how strong Sam gets, nearly all of the
models indicate that it will remain a powerful hurricane during the
next several days.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 12.8N 46.7W 95 KT 110 MPH
12H 25/1800Z 13.1N 48.0W 110 KT 125 MPH
24H 26/0600Z 13.5N 49.3W 115 KT 130 MPH
36H 26/1800Z 14.0N 50.4W 120 KT 140 MPH
48H 27/0600Z 14.7N 51.5W 120 KT 140 MPH
60H 27/1800Z 15.4N 52.5W 115 KT 130 MPH
72H 28/0600Z 16.3N 53.7W 115 KT 130 MPH
96H 29/0600Z 18.0N 56.0W 110 KT 125 MPH
120H 30/0600Z 20.1N 59.0W 110 KT 125 MPH

$$
Forecaster Cangialosi
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Re: ATL: SAM - Advisories

#12 Postby cycloneye » Sat Sep 25, 2021 9:43 am

BULLETIN
Hurricane Sam Advisory Number 12
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Sat Sep 25 2021

...SMALL BUT DANGEROUS SAM NOW A MAJOR HURRICANE...
...SOME ADDITIONAL STRENGTHENING EXPECTED THIS WEEKEND...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...12.9N 47.6W
ABOUT 1095 MI...1760 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...120 MPH...195 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...960 MB...28.35 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Hurricane Sam was located
near latitude 12.9 North, longitude 47.6 West. Sam is moving toward
the west-northwest near 10 mph (17 km/h). A slower motion to the
west-northwest is expected over the weekend, followed by a turn to
the northwest on Monday.

Maximum sustained winds have increased to near 120 mph (195 km/h)
with higher gusts. Sam is a category 3 hurricane on the
Saffir-Simpson Hurricane Wind Scale. Additional strengthening is
expected over the next day or so, and Sam is forecast to become a
category 4 hurricane by Sunday. Some fluctuations in the hurricane's
intensity are possible early next week.

Sam is a small hurricane. Hurricane-force winds extend outward up to
25 miles (35 km) from the center and tropical-storm-force winds
extend outward up to 105 miles (165 km).

The estimated minimum central pressure is 960 mb (28.35 inches).


HAZARDS AFFECTING LAND
----------------------
SURF: Swells generated by Sam are forecast to reach the Lesser
Antilles early next week. These swells could cause life-threatening
surf and rip current conditions. Please consult products from your
local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 500 PM AST.

$$
Forecaster Latto



Hurricane Sam Discussion Number 12
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Sat Sep 25 2021

Sam has continued to intensify this morning and now has a complete
ring of deep convection with cloud tops colder than -70 degrees C
surrounding a mostly clear, small eye. The latest subjective Dvorak
intensity estimates from TAFB and SAB are both 102 kt, while the
combined objective Dvorak intensity estimates from the UW-CIMSS
SATCON and ADT is 110 kt. Based on this data, the initial intensity
has been increased to 105 kt for this advisory, making Sam a major
hurricane. The cyclone remains compact, with hurricane-force winds
extending only 20 n mi from the center.

The hurricane wobbled to the west over the past few hours. However,
the 12-hour motion is west-northwest at 9 kt. There are no changes
to the forecast track reasoning. The ridge the north of Sam
responsible for its current motion is forecast to shift to the east
in a couple of days as a deep-layer trough establishes itself over
the western Atlantic. Sam is forecast to turn northwestward around
the southwestern periphery of the ridge in about 48 h, and gradually
increase its forward speed thereafter. The model guidance continues
to be in very good agreement with this scenario, and the latest NHC
track forecast is unchanged from the previous one. It should be
noted that the westernmost guidance continues to be the ECMWF
ensemble mean, whose members have had a low bias in the intensity of
Sam, which is likely contributing to the westward track bias. Based
on the NHC forecast, and all of the other guidance, Sam is expected
to still be well to the east or northeast of the northern Leeward
Islands through day 5.

Environmental conditions support further strengthening in the short
term, and Sam is expected to become a category 4 hurricane by
Sunday. In a few days, some southwesterly shear is forecast to
develop as the cyclone begins to round the periphery of the
subtropical ridge. Although this should cause Sam to weaken, it is
still expected to remain a powerful hurricane throughout the 5-day
forecast period. The latest NHC intensity forecast is near the
previous one, which remains slightly above the various consensus
solutions through 72 h, and then closely follows the consensus
thereafter.


FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 12.9N 47.6W 105 KT 120 MPH
12H 26/0000Z 13.3N 48.7W 110 KT 125 MPH
24H 26/1200Z 13.7N 49.8W 115 KT 130 MPH
36H 27/0000Z 14.3N 50.8W 120 KT 140 MPH
48H 27/1200Z 15.0N 51.9W 120 KT 140 MPH
60H 28/0000Z 15.8N 53.0W 115 KT 130 MPH
72H 28/1200Z 16.6N 54.1W 115 KT 130 MPH
96H 29/1200Z 18.4N 56.5W 110 KT 125 MPH
120H 30/1200Z 20.7N 59.8W 110 KT 125 MPH

$$
Forecaster Latto
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Re: ATL: SAM - Advisories

#13 Postby cycloneye » Sat Sep 25, 2021 3:42 pm

Hurricane Sam Discussion Number 13
NWS National Hurricane Center Miami FL AL182021
500 PM AST Sat Sep 25 2021

After a brief hiccup, Sam has resumed rapid strengthening and now
shows a 12-15 n mi wide well-defined eye embedded in a central
dense overcast with cloud tops colder than -70C. Subjective
satellite intensity estimates from TAFB and SAB were 115 kt at 18Z,
and objective intensity estimates have also been near 115 kt.
Since the organization has increased some since 18Z, the initial
intensity is increased to 120 kt. A NOAA Hurricane Hunter aircraft
is currently enroute to Sam to provide a better estimate of the
intensity. The hurricane has good cirrus outflow in all quadrants.
However, a large arc cloud to the northwest of the central core
suggests dry air is present in that area.

The initial motion is still west-northwestward or 290/9. There are
again no changes to the forecast track reasoning. The weak
subtropical ridge currently to the north of Sam is forecast to shift
eastward as a large deep-layer mid-latitude trough develops over the
western Atlantic. This evolution should cause Sam to continue
west-northwestward with some decrease in forward speed during the
next couple of days, followed by a turn toward the northwest. Some
increase in forward speed is likely by 120 h as Sam encounters
stronger steering flow. The track guidance has shifted a little to
the north and east since the previous advisory, and the new forecast
track is also nudged in that direction, with the new track lying
between the HCCA corrected consensus model and the other consensus
models. Based on the NHC forecast, and all of the other guidance,
Sam is expected to still be well to the east or northeast of the
northern Leeward Islands through day 5.

The current strengthening is expected to continue for the next
6-12 h, and based on this the new intensity forecast now calls for a
peak intensity of 130 kt. After the peak, Sam is expected to be in
an environment of warm sea surface temperatures and light wind
shear for at least the next 3-4 days. This suggests the intensity
will be controlled mainly by eyewall replacement cycles and
possible intrusions of dry air, which would cause some short-term
fluctuations in intensity. In the bigger picture, the intensity
guidance calls for a slow weakening during the 24-120 h forecast
period, and the new intensity forecast does the same. However, it
is likely that Sam will remain a major hurricane through 120 h.


FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 13.3N 48.5W 120 KT 140 MPH
12H 26/0600Z 13.7N 49.4W 130 KT 150 MPH
24H 26/1800Z 14.3N 50.5W 125 KT 145 MPH
36H 27/0600Z 14.9N 51.6W 120 KT 140 MPH
48H 27/1800Z 15.7N 52.7W 120 KT 140 MPH
60H 28/0600Z 16.6N 53.9W 115 KT 130 MPH
72H 28/1800Z 17.4N 55.0W 115 KT 130 MPH
96H 29/1800Z 19.5N 58.0W 110 KT 125 MPH
120H 30/1800Z 22.5N 61.0W 110 KT 125 MPH

$$
Forecaster Beven
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Re: ATL: SAM - Advisories

#14 Postby cycloneye » Sat Sep 25, 2021 9:52 pm

BULLETIN
Hurricane Sam Advisory Number 14
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Sat Sep 25 2021

...NOAA HURRICANE HUNTER AIRCRAFT FINDS THAT SAM HAS CONTINUED TO
RAPIDLY INTENSIFY...
...FLUCTUATIONS IN INTENSITY LIKELY DURING THE NEXT DAY OR SO...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...13.5N 49.0W
ABOUT 990 MI...1595 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...145 MPH...230 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...943 MB...27.85 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located
near latitude 13.5 North, longitude 49.0 West. Sam is moving toward
the west-northwest near 8 mph (13 km/h), and this general motion is
forecast to continue through Sunday. A turn toward the northwest is
expected on Monday.

Maximum sustained winds are near 145 mph (230 km/h) with higher
gusts. Sam is a category 4 hurricane on the Saffir-Simpson
Hurricane Wind Scale. Fluctuations in intensity are likely into
early next week.

Sam remains a small hurricane. Hurricane-force winds extend outward
up to 30 miles (45 km) from the center and tropical-storm-force
winds extend outward up to 105 miles (165 km).

The estimated minimum central pressure based on data from the NOAA
reconnaissance aircraft is 943 mb (27.85 inches).


HAZARDS AFFECTING LAND
----------------------
SURF: Swells generated by Sam are forecast to reach the Lesser
Antilles early next week. These swells could cause life-threatening
surf and rip current conditions. Please consult products from your
local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 500 AM AST.

$$
Forecaster Stewart



Hurricane Sam Discussion Number 14
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Sat Sep 25 2021

It's been an interesting evening with regards to analyzing the
various data from a NOAA Hurricane Hunter research flight into
Hurricane Sam. Dropsonde data in both the southeast and northwest
quadrants indicate that small eyewall mesovortices and possibly even
tornado-scale vortices were present based on the wind profiles
showing sharply opposite-direction winds from what would normally be
expected in those regions of the hurricane. Some dropsonde surface
winds have been as high as 162 kt, which is more representative of a
gust, while SFMR surface winds have been as high as 133 kt. However,
the strongest 700-mb flight-level winds have been 138-139 kt in the
northeastern quadrant, which equates to about 125-kt tangential
surface winds. Three dropsondes released in the eye indicate that
the pressure had remained steady at 943-944 mb during the duration
of the aircraft reconnoiter. That pressure equates to about 125 kt
based on various pressure-wind relationships. Based on that estimate
and the 700-mb flight-level to surface-wind conversion, the advisory
intensity is 125 kt, which is representative of the mean tangential
winds and no localized wind perturbations.

The initial motion is toward the west-northwest, or 295/07 kt.
Not to sound like a broken record, but no significant changes were
made to the previous track forecast and reasoning. Sam is expected
to move slowly west-northwestward and northwestward over the next
few days around the southwestern periphery of a deep-layer
subtropical ridge that is situated to the north and northeast of the
small hurricane. On days 4 and 5, an upper-level trough/low is
forecast to dig southward and amplify off the U.S. east coast and
extend all the way to the Bahamas. This feature should act to lift
Sam northward at a faster forward speed. The latest NHC model
guidance based on 12Z and 18Z model runs has shifted noticeably to
the east of the previous runs, and the new NHC track forecast has
been nudged in that direction as well. However, since the NOAA G-IV
jet aircraft has been out there sampling the environment around
Sam, it's best to remain conservative and not shift the track any
farther to the east until the new 00Z model runs with that new
aircraft data come in for the next advisory package at 0600Z. The
new NHC track forecast lies about halfway between the previous
advisory track on the left and the tightly packed consensus track
models on the right.

The radar images from the reconnaissance aircraft indicated that the
eyewall was thin in many locations due to dry-air intrusions, and
the latest SHIPS intensity output indicates that Sam will remain
within a fairly dry mid-level environment. Also, the depth of the
warm water beneath the hurricane isn't overly deep, which could
result in cold upwelling owing to Sam's slow forward motion of only
5-7 kt during the next couple of days. Eyewall replacement cycles
are also likely now due to the hurricane's small size and strong
intensity. Thus, fluctuations in intensity seem likely for the next
couple of days even though the vertical wind shear is expected to
remain quite low at only 5-10 kt. On days 3-5, however, the shear is
forecast to increase to 15-20 kt from the southwest, which is
expected to induce a slow weakening trend. However, it is likely
that Sam will remain a major hurricane through 120 h, even on days
3-5 due to the cyclone moving over warmer and deeper water during
that 3-day period. The new official intensity forecast is
essentially the same as the previous advisory, and remains above the
consensus model and is near the higher end of the intensity
guidance.

FORECAST POSITIONS AND MAX WINDS

INIT 26/0300Z 13.5N 49.0W 125 KT 145 MPH
12H 26/1200Z 14.0N 49.9W 130 KT 150 MPH
24H 27/0000Z 14.7N 51.0W 125 KT 145 MPH
36H 27/1200Z 15.4N 52.1W 120 KT 140 MPH
48H 28/0000Z 16.3N 53.2W 120 KT 140 MPH
60H 28/1200Z 17.1N 54.3W 115 KT 130 MPH
72H 29/0000Z 18.0N 55.6W 115 KT 130 MPH
96H 30/0000Z 20.1N 58.5W 110 KT 125 MPH
120H 01/0000Z 23.7N 61.4W 110 KT 125 MPH

$$
Forecaster Stewart

NNNN
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Re: ATL: SAM - Advisories

#15 Postby cycloneye » Sun Sep 26, 2021 3:54 am

BULLETIN
Hurricane Sam Advisory Number 15
NWS National Hurricane Center Miami FL AL182021
500 AM AST Sun Sep 26 2021

...SAM REMAINS A CATEGORY FOUR HURRICANE...
...FLUCTUATIONS IN INTENSITY LIKELY DURING THE NEXT DAY OR SO...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...13.8N 49.7W
ABOUT 940 MI...1510 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...145 MPH...230 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...943 MB...27.85 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 AM AST (0900 UTC), the center of Hurricane Sam was located
near latitude 13.8 North, longitude 49.7 West. Sam is moving toward
the west-northwest near 8 mph (13 km/h). This general motion is
expected to continue today, followed by a turn toward the northwest
on Monday. Then, a northwestward motion is forecast to continue
through midweek.

Maximum sustained winds are near 145 mph (230 km/h) with higher
gusts. Sam is a category 4 hurricane on the Saffir-Simpson
Hurricane Wind Scale. Some fluctuations in intensity are expected
during the next day or so. Thereafter, some slow weakening is
forecast.

Sam is a small hurricane. Hurricane-force winds extend outward up
to 30 miles (45 km) from the center and tropical-storm-force winds
extend outward up to 90 miles (150 km).

The estimated minimum central pressure is 943 mb (27.85 inches).


HAZARDS AFFECTING LAND
----------------------
SURF: Swells generated by Sam are forecast to reach the Lesser
Antilles early this week. These swells could cause life-threatening
surf and rip current conditions. Please consult products from your
local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.

$$
Forecaster Reinhart




Hurricane Sam Discussion Number 15
NWS National Hurricane Center Miami FL AL182021
500 AM AST Sun Sep 26 2021

Sam remains a small but intense hurricane this morning, with a
well-defined 10 n mi-wide eye. A 0500 UTC AMSR-2 microwave pass
reveals Sam has a compact inner core of deep convection surrounding
its eye, with curved convective bands primarily extending around the
northern and eastern portions of the circulation. Infrared cloud top
temperatures briefly warmed overnight in portions of Sam's central
dense overcast, perhaps due to some intrusions of drier mid-level
air. The 06z objective and subjective satellite estimates ranged
from 113-127 kt, but Sam's satellite presentation has improved in
recent infrared imagery as cloud top temperatures are cooling around
the eye. Thus, the initial intensity is held at 125 kt for this
advisory. NOAA aircraft are scheduled to investigate Sam later this
afternoon, which should provide helpful information about the
structure and intensity of the hurricane.

Sam is moving toward the west-northwest, or 295/7 kt. A deep-layer
subtropical ridge to the north and northeast of Sam should generally
steer the hurricane west-northwestward to northwestward for the next
several days. By midweek, an amplifying upper-level trough will move
off the east coast of the U.S. and dig southward over the western
Atlantic, which will erode the western extent of the steering ridge.
The deep-layer southerly flow ahead of the trough should cause Sam
to begin recurving, with a somewhat faster north-northwestward
motion forecast by day 5. The latest NHC track forecast is very
similar to the previous one and generally lies between the HFIP
corrected consensus approach (HCCA) and TVCA aids. At days 4-5,
there is more spread in the track guidance, with the ECMWF on the
far left side of the guidance envelope and the GFS on the far right.
The NHC forecast track has been nudged just slightly to the left at
96 and 120 h, but it still lies to the right of HCCA.

The hurricane will likely experience some fluctuations in intensity
during the next day or two. On the one hand, Sam remains over warm
sea-surface temperatures of around 28.5 deg C, with vertical wind
shear less than 10 kt as diagnosed from the SHIPS guidance. However,
GOES-16 water vapor imagery shows some drier mid-level air in the
surrounding environment that may periodically entrain into the inner
core of Sam. Additionally, the onset of an eyewall replacement cycle
remains a distinct possibility at this stage of Sam's life cycle,
although the latest microwave data does not suggest one is imminent.
The official NHC intensity forecast lies on the high end of the
guidance for the first 36-48 h of the forecast period. Thereafter,
the NHC forecast trends closer to the HCCA and IVCN consensus aids.
Some gradual weakening is forecast later in the period as the
southwesterly vertical wind shear begins to increase, but Sam is
still forecast to remain a major hurricane through the 5-day period.


FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 13.8N 49.7W 125 KT 145 MPH
12H 26/1800Z 14.3N 50.6W 125 KT 145 MPH
24H 27/0600Z 15.0N 51.8W 120 KT 140 MPH
36H 27/1800Z 15.8N 52.9W 120 KT 140 MPH
48H 28/0600Z 16.6N 53.9W 115 KT 130 MPH
60H 28/1800Z 17.5N 55.0W 115 KT 130 MPH
72H 29/0600Z 18.4N 56.3W 115 KT 130 MPH
96H 30/0600Z 20.8N 59.3W 110 KT 125 MPH
120H 01/0600Z 24.5N 62.0W 110 KT 125 MPH

$$
Forecaster Reinhart
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Re: ATL: SAM - Advisories

#16 Postby cycloneye » Sun Sep 26, 2021 3:39 pm

BULLETIN
Hurricane Sam Advisory Number 17
NWS National Hurricane Center Miami FL AL182021
500 PM AST Sun Sep 26 2021

...SMALL BUT FEROCIOUS SAM STRENGTHENS SOME MORE...
...EXPECTED TO REMAIN A MAJOR HURRICANE FOR SEVERAL DAYS


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...14.2N 50.5W
ABOUT 880 MI...1415 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...150 MPH...240 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...938 MB...27.70 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Hurricane Sam was located
near latitude 14.2 North, longitude 50.5 West. Sam is moving toward
the northwest near 7 mph (11 km/h) and this motion is expected to
continue for the next few days, along with a gradual increase in
forward speed commencing by midweek.

Maximum sustained winds have increased to near 150 mph (240 km/h)
with higher gusts. Sam is a category 4 hurricane on the
Saffir-Simpson Hurricane Wind Scale. Some fluctuations in intensity
are expected during the next couple of days. Thereafter, some slow
weakening is forecast.

Sam is a small tropical cyclone. Hurricane-force winds extend
outward up to 30 miles (45 km) from the center and
tropical-storm-force winds extend outward up to 90 miles (150 km).

The estimated minimum central pressure is 938 mb (27.70 inches).


HAZARDS AFFECTING LAND
----------------------
SURF: Swells generated by Sam are forecast to reach the Lesser
Antilles early this week. These swells could cause life-threatening
surf and rip current conditions. Please consult products from your
local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Latto




Hurricane Sam Discussion Number 17
NWS National Hurricane Center Miami FL AL182021
500 PM AST Sun Sep 26 2021

Sam has found a way to strengthen some more today. The ring of
intense convection surrounding the 15-n-mi-diameter eye has expanded
in size over the past several hours, while cloud tops colder than
-70C still completely surround the center. An earlier GMI microwave
overpass revealed very strong eyewall convection tightly wrapped
around the small eye, a feature oftentimes seen with intense
hurricanes. The latest Dvorak intensity estimates from TAFB and SAB
remain T6.5/127 kt. However, the UW-CIMSS ADT estimate has recently
increased to T6.6/130 kt. Based on the expansion of the ring of
convection and a blend of these Dvorak estimates, the initial
intensity is raised to 130 kt for this advisory. Sam remains
compact, with winds of tropical storm force extending only 70 n mi
from the center. A NOAA Hurricane Hunter aircraft is en route to
investigate Sam and will provide more detailed intensity data.

It would not take much further expansion of the convection and
cooling of the cloud tops over the inner-most core of Sam for it to
become a rare Category 5 hurricane on the Saffir-Simpson hurricane
wind scale. Although plausible given the ideal environmental
conditions over the next couple of days, this strengthening is not
explicitly forecast to occur. The only factors within the next 2-3
days that could cause Sam to weaken would be an eyewall replacement
cycle or the upwelling of cooler waters due to the hurricane's
relatively slow forward motion. By 72 h, vertical wind shear is
forecast to increase, which should cause gradual weakening. However,
given the current strength of Sam, the new forecast calls for it to
remain a major hurricane throughout the 5-day forecast period. The
latest NHC intensity forecast was increased by 5 kt through 60 h due
to the change in the initial intensity and remains on the high end
of the guidance through that time. At 72 h and beyond, the intensity
forecast is near the HFIP corrected consensus approach (HCCA) model.

Sam has been wobbling a little north-northwestward and has slowed
down over the past few hours, but the 12-h-average motion is about
305/06 kt. A subtropical ridge centered to the northeast of the
hurricane should steer it northwestward for the next 3-4 days. By
late Thursday, Sam is expected to reach the western periphery of the
ridge and turn north-northwestward and begin to increase its forward
speed as the cyclone starts to get caught up in the southerly flow
between the ridge and an approaching mid-latitude trough. The
various track model guidance is in better agreement today compared
to yesterday, especially in the day 3-5 time frame. The latest NHC
track forecast is little changed from the previous one, and lies
near the various consensus track model solutions.


FORECAST POSITIONS AND MAX WINDS

INIT 26/2100Z 14.2N 50.5W 130 KT 150 MPH
12H 27/0600Z 14.7N 51.3W 130 KT 150 MPH
24H 27/1800Z 15.5N 52.5W 125 KT 145 MPH
36H 28/0600Z 16.3N 53.6W 125 KT 145 MPH
48H 28/1800Z 17.2N 54.7W 120 KT 140 MPH
60H 29/0600Z 18.1N 55.8W 120 KT 140 MPH
72H 29/1800Z 19.2N 57.4W 115 KT 130 MPH
96H 30/1800Z 22.1N 60.5W 110 KT 125 MPH
120H 01/1800Z 26.6N 62.9W 110 KT 125 MPH

$$
Forecaster Latto
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Re: ATL: SAM - Advisories

#17 Postby cycloneye » Sun Sep 26, 2021 9:52 pm

BULLETIN
Hurricane Sam Advisory Number 18
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Sun Sep 26 2021

...HURRICANE HUNTER AIRCRAFT FINDS SAM HAS PEAKED IN INTENSITY...
...EXPECTED TO REMAIN A MAJOR HURRICANE FOR SEVERAL DAYS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...14.7N 50.8W
ABOUT 850 MI...1365 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...145 MPH...230 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...943 MB...27.85 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Hurricane Sam was located
by a NOAA Hurricane Hunter aircraft near latitude 14.7 North,
longitude 50.8 West. Sam is moving toward the northwest near 7 mph
(11 km/h), and this motion is expected to continue for the next few
days, along with a gradual increase in forward speed beginning
around midweek.

Data from the reconnaissance aircraft indicate that maximum
sustained winds are near 145 mph (230 km/h) with higher gusts. Sam
is a category 4 hurricane on the Saffir-Simpson Hurricane Wind
Scale. Some fluctuations in intensity are expected during the next
day or so. Thereafter, slow weakening is forecast. However, Sam is
still expected to remain a major hurricane through midweek.

Sam remains a small tropical cyclone. Hurricane-force winds extend
outward up to 30 miles (45 km) from the center and
tropical-storm-force winds extend outward up to 90 miles (150 km).

The estimated minimum central pressure based on recent reports from
the aircraft is 943 mb (27.85 inches).


HAZARDS AFFECTING LAND
----------------------
SURF: Swells generated by Sam are forecast to reach the Lesser
Antilles early this week. These swells could cause life-threatening
surf and rip current conditions. Please consult products from your
local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 500 AM AST.

$$
Forecaster Stewart


Hurricane Sam Discussion Number 18
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Sun Sep 26 2021

A NOAA Hurricane Hunter aircraft investigating Sam this afternoon
and evening found that the major hurricane likely peaked in
intensity at around 135 kt with a central pressure of about 929 mb
between 1900-2200 UTC when the eye contracted down to about 7 nmi in
diameter. Since that time, however, wind and radar data from the
aircraft reveal that Sam has been undergoing an eyewall replacement
cycle (ERC), including significant erosion of the eyewall convection
in the eastern semicircle, which has resulted in the central
pressure increasing by at least 14 mb in only a few hours. The eye
diameter has also doubled in size now. The ERC is also confirmed by
the ragged inner-core convection and cloud-filled eye that have
developed in satellite imagery. The advisory intensity of 125 kt is
based on a blend of the available reliable SFMR surface wind data
and flight-level wind data, and also using the pressure-wind
relationship for a 943-mb central pressure.

The initial motion estimate is now 315/06 kt. A strong subtropical
ridge to the north and northeast of Sam is forecast by the global
and regional models to remain entrenched across the central and
eastern Atlantic for the next several days, resulting in the
hurricane moving northwestward for the 72 hours. Thereafter, a mid-
to upper-level trough is forecast to dig southward just off the U.S.
east coast, creating a deep southerly flow regime that will act to
accelerate Sam northward on days 4 and 5. The new NHC track
forecast is similar the previous advisory, and lies close to the
tightly packed consensus models through 72 hours. In the 96-120 hour
period, the models diverge significantly on when and where Sam will
begin moving out toward the north, and the NHC track forecast
favors the more eastward GFS solution since that model has been
performing quite well with Sam thus far.

Now that Sam is undergoing an ERC, fluctuations in intensity could
occur for the next day or two while the vertical wind shear remains
low at least than 10 kt. Thereafter, a slow weakening trend is
expected due to a modest increase in the wind shear from the
southwest and occasional intrusions of drier mid-level air. The NHC
intensity forecast is a little lower than the previous advisory,
mainly due to the lower initial intensity, and closely follows the
HCCA and IVCN consensus model intensity forecasts.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0300Z 14.7N 50.8W 125 KT 145 MPH
12H 27/1200Z 15.3N 51.6W 125 KT 145 MPH
24H 28/0000Z 16.2N 52.8W 120 KT 140 MPH
36H 28/1200Z 17.0N 53.9W 120 KT 140 MPH
48H 29/0000Z 17.8N 55.0W 120 KT 140 MPH
60H 29/1200Z 18.7N 56.3W 115 KT 130 MPH
72H 30/0000Z 20.0N 58.0W 115 KT 130 MPH
96H 01/0000Z 23.4N 61.0W 110 KT 125 MPH
120H 02/0000Z 28.4N 62.6W 105 KT 120 MPH

$$
Forecaster Stewart
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Re: ATL: SAM - Advisories

#18 Postby cycloneye » Mon Sep 27, 2021 4:26 am

Hurricane Sam Discussion Number 19
NWS National Hurricane Center Miami FL AL182021
500 AM AST Mon Sep 27 2021

The satellite presentation of Sam deteriorated overnight, as GOES-16
infrared imagery showed periodic disruptions to Sam's inner core
convection. The eye has not been readily apparent in conventional
satellite imagery for much of the night, although very recent
imagery suggests an eye could be re-emerging. Data from the
reconnaissance aircraft last night indicated that an eyewall
replacement cycle (ERC) was underway, and some dry mid-level air
impinging on the western side of the circulation could also be
negatively impacting Sam. No recent high-resolution microwave data
is available, but an earlier scatterometer pass revealed that the
tropical-storm-force wind radii had expanded just a bit in the
eastern semicircle of the hurricane. The initial intensity is
lowered to 115 kt for this advisory based on a blend of the
objective and subjective Dvorak current intensity estimates. A NOAA
hurricane hunter aircraft is scheduled to investigate Sam later this
morning, which will provide crucial data to assess changes in Sam's
structure and intensity.

The initial motion is estimated to be northwestward, or 315/7 kt. A
subtropical ridge to the north and northeast of Sam will remain the
primary steering mechanism over the next several days, and Sam is
expected to maintain a northwestward heading through midweek. Then,
a mid- to upper-level trough is forecast to dig southward over the
western Atlantic late this week. The deep-layer southerly flow ahead
of this feature should cause Sam to move faster toward the
north-northwest by 96 h, followed by a northward acceleration
thereafter. The NHC forecast track is shifted slightly to the right
of the previous one through the first 48-60 h of the forecast
period, which accounts for the more northwestward initial motion
observed during the past 12 h. Otherwise, the NHC track is virtually
unchanged as the guidance has remained fairly consistent.

Sam's intensity has likely peaked now that an ERC has commenced, but
environmental conditions should allow Sam to persist as a major
hurricane for the next several days. Sea-surface temperatures are
expected to be 28 deg C or greater along Sam's track through 120 h,
and the vertical wind shear is forecast to remain weak (< 10 kt)
through at least midweek. Thus, the official NHC intensity forecast
only shows very gradual weakening during the next several days,
generally following the HCCA and IVCN consensus aids. Given the
lower initial intensity of Sam, the latest NHC forecast is once
again lower than the previous one. By 120 h, southerly shear
associated with the deep-layer trough is forecast to increase over
Sam, which should induce more weakening by this weekend.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0900Z 15.2N 51.4W 115 KT 130 MPH
12H 27/1800Z 15.9N 52.2W 115 KT 130 MPH
24H 28/0600Z 16.8N 53.3W 115 KT 130 MPH
36H 28/1800Z 17.7N 54.4W 115 KT 130 MPH
48H 29/0600Z 18.6N 55.6W 110 KT 125 MPH
60H 29/1800Z 19.6N 57.1W 110 KT 125 MPH
72H 30/0600Z 21.0N 58.8W 110 KT 125 MPH
96H 01/0600Z 24.9N 61.6W 110 KT 125 MPH
120H 02/0600Z 30.5N 62.0W 105 KT 120 MPH

$$
Forecaster Reinhart
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Re: ATL: SAM - Advisories

#19 Postby cycloneye » Mon Sep 27, 2021 10:00 am

BULLETIN
Hurricane Sam Advisory Number 20
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Mon Sep 27 2021

...HURRICANE HUNTER AIRCRAFT CURRENTLY INVESTIGATING SAM...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.7N 52.1W
ABOUT 745 MI...1200 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...125 MPH...205 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...966 MB...28.53 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Hurricane Sam was located
near latitude 15.6 North, longitude 52.0 West. Sam is moving toward
the northwest near 8 mph (13 km/h) and this motion is expected to
continue for the next few days, with an increase in forward speed
beginning on Thursday. A turn to the north is expected on Friday.
On the forecast track, Sam will pass well to the northeast of the
northern Leeward Islands Wednesday and Thursday.

Maximum sustained winds are near 125 mph (205 km/h) with higher
gusts. Sam is a category 3 hurricane on the Saffir-Simpson
Hurricane Wind Scale. Fluctuations in intensity are possible
during the next days, although Sam is forecast to remain a major
hurricane through at least Thursday night.

Hurricane-force winds extend outward up to 30 miles (45 km) from the
center and tropical-storm-force winds extend outward up to 105 miles
(165 km).

The minimum central pressure estimated from NOAA Hurricane Hunter
aircraft observations is 966 mb (28.53 inches).


HAZARDS AFFECTING LAND
----------------------
SURF: Swells generated by Sam will reach the Lesser Antilles today
and impact these islands for the next several days. Swells are
expected to reach Bermuda and the Bahamas mid-to-late week, and
then spread to the United States east coast late this week. These
swells could cause life-threatening surf and rip current conditions.
Please consult products from your local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 500 PM AST.

$$
Forecaster Hagen/Pasch



Hurricane Sam Discussion Number 20
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Mon Sep 27 2021

Sam appeared weaker on satellite images earlier this morning, and
the eye was not apparent in visible or infrared satellite imagery.
However, a 27/0741 UTC SSMIS pass still showed a well-defined eye.
Recent visible and infrared images from the past couple of
hours however, show that the structure is becoming better organized
again, with the eye again becoming apparent on visible satellite.
A NOAA Hurricane Hunter aircraft has made one pass through the
hurricane so far and found that the central pressure has risen to
about 966 mb. The current intensity estimate is reduced slightly
to 110 kt. The aircraft has not yet sampled the northeast
quadrant, where the strongest winds are likely occurring.

The initial motion is estimated to be northwestward, or 310/7. A
subtropical ridge to the north and northeast of Sam will remain the
primary steering mechanism over the next several days, and Sam is
expected to continue on a similar heading through the next 72 hours
or so. A mid- to upper-level trough is forecast to emerge off the
U.S. Northeast and Mid-Atlantic coast and dig southward over the
western Atlantic late this week. The deep-layer southerly flow
ahead of this feature should cause Sam to accelerate to the
north-northwest by late Thursday and then turn northward on Friday.
The NHC forecast track is largely unchanged from the previous,
except it is shifted ever so slightly westward at the hour 72 and 96
points, about midway between the previous NHC forecast and the
latest HCCA consensus. The confidence in the track forecast is
medium to high through 3 to 4 days. Beyond that time, confidence is
about average, as there is some increase in model spread noted.

Regarding the intensity forecast, Sam is forecast to travel over
warm ocean temperatures while it remains in an environment of low
vertical wind shear through the next 4 days. Some mid-level dry
air noted on water vapor channels to the west of Sam could play a
role in limiting Sam's intensity through hour 48. However, the
environment could become more moist again after that time. Due to
these competing factors, I opted to hold the intensity steady for
the next several days, although fluctuations in intensity can be
expected. The NHC intensity forecast is above all model
guidance through hour 60, and is in agreement with the model
consensus at hour 72-96. After that time, increasing wind shear
induced by the approaching mid- to upper-level trough to the
northwest of the cyclone should cause weakening.


FORECAST POSITIONS AND MAX WINDS

INIT 27/1500Z 15.7N 52.1W 110 KT 125 MPH
12H 28/0000Z 16.4N 52.8W 110 KT 125 MPH
24H 28/1200Z 17.3N 53.9W 110 KT 125 MPH
36H 29/0000Z 18.1N 55.1W 110 KT 125 MPH
48H 29/1200Z 19.1N 56.5W 110 KT 125 MPH
60H 30/0000Z 20.2N 58.1W 110 KT 125 MPH
72H 30/1200Z 21.7N 59.8W 110 KT 125 MPH
96H 01/1200Z 25.9N 62.2W 110 KT 125 MPH
120H 02/1200Z 32.0N 61.3W 100 KT 115 MPH

$$
Forecaster Hagen/Pasch
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Re: ATL: SAM - Advisories

#20 Postby cycloneye » Mon Sep 27, 2021 3:54 pm

Hurricane Sam Advisory Number 21
NWS National Hurricane Center Miami FL AL182021
500 PM AST Mon Sep 27 2021

...SAM BEGINNING TO REGROUP AFTER WEAKENING...
...SOME REINTENSIFICATION EXPECTED THROUGH TONIGHT...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...16.3N 52.7W
ABOUT 700 MI...1125 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...120 MPH...195 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...957 MB...28.26 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Hurricane Sam was located
near latitude 16.3 North, longitude 52.7 West. Sam is moving toward
the northwest near 9 mph (15 km/h), and this motion is expected to
continue for the next few days, with an increase in forward speed
beginning on Thursday. A turn to the north is expected by Friday.
On the forecast track, Sam will pass well to the northeast of the
northern Leeward Islands Wednesday and Thursday.

An Air Force Reserve Hurricane Hunter aircraft indicates that the
maximum sustained winds are near 120 mph (195 km/h) with higher
gusts. Sam is a category 3 hurricane on the Saffir-Simpson
Hurricane Wind Scale. Some strengthening is expected through
tonight. Thereafter, fluctuations in intensity are possible through
Thursday.

Hurricane-force winds extend outward up to 30 miles (45 km) from the
center and tropical-storm-force winds extend outward up to 105 miles
(165 km).

The minimum central pressure measured by the aircraft is 957 mb
(28.26 inches).


HAZARDS AFFECTING LAND
----------------------
Key messages for Sam can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT3 and WMO header WTNT43 KNHC.

SURF: Swells generated by Sam will impact the Lesser Antilles for
the next several days. Swells are expected to reach Bermuda and the
Bahamas mid-to-late week, and then spread to the United States east
coast late this week. These swells could cause life-threatening
surf and rip current conditions. Please consult products from your
local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Latto



Hurricane Sam Discussion Number 21
NWS National Hurricane Center Miami FL AL182021
500 PM AST Mon Sep 27 2021

Sam's weakening trend ended earlier today, with the intensity likely
bottoming out between the issuance of the previous advisory and now.
Over the past few hours, microwave data and satellite imagery
indicate that the inner core and eyewall of the hurricane are making
a comeback. There is now a clear eye in visible imagery, convective
cloud tops colder than -65 degrees C wrap completely around the
center, and the convective mass is becoming more circular once
again. An Air Force Reserve Hurricane Hunter aircraft currently
investigating Sam indicates the central pressure has dropped to 957
mb, with peak 700-mb flight-level winds of 106 kt, SFMR values of
100 kt, and dropsonde surface winds of 102 kt. Given possible minor
undersampling and the recent dropping of the hurricane's pressure,
the initial advisory intensity is set at 105 kt.

Sam continues to move northwest, or 315/8 kt. The hurricane is
expected to continue this northwestward motion around a subtropical
ridge over the next few days. By late Thursday or early Friday a
turn toward the north is anticipated as Sam rounds the western
periphery of the ridge. The cyclone should begin to gradually
accelerate during that time in the increasing flow ahead of a mid-
to upper-level trough emerging off the U.S. east coast later this
week. Model guidance remains in very good agreement on this
scenario and the latest NHC forecast track is little changed from
the previous one, and lies near tightly clustered consensus track
guidance.

The southwesterly winds that brought in some dry air and disrupted
Sam's impressive satellite appearance last night appear to have
abated. As long as environmental winds surrounding the hurricane
remain light, then the dry air surrounding the cyclone should not
have as much of an impact on the hurricane's strength over the next
few days. Based on the improving inner-core structure appearance of
Sam, re-strengthening is forecast over the next 12 h. Thereafter,
mainly minor fluctuations in intensity are indicated through 72 h.
Beyond that time, increasing vertical wind shear and decreasing
sea-surface temperatures should cause Sam to weaken. The latest NHC
intensity forecast was nudged slightly upward through 36 h and is
on the high end of the guidance. Thereafter, no changes were made,
and that portion of the forecast is close to the various multimodel
consensus solutions.

Key Messages:

1. Large swells generated by Sam are affecting the Leeward Islands
and will spread to portions of the Virgin Islands, Puerto Rico,
Hispaniola, the Bahamas, and Bermuda by Thursday or Friday.
Significant swells will likely reach the east coast of the United
States and Atlantic Canada by the weekend. These swells will likely
cause life-threatening surf and rip current conditions, and
beachgoers and other interests along these coasts are urged to
follow the advice of lifeguards and local officials through the
upcoming weekend.


FORECAST POSITIONS AND MAX WINDS

INIT 27/2100Z 16.3N 52.7W 105 KT 120 MPH
12H 28/0600Z 17.0N 53.5W 115 KT 130 MPH
24H 28/1800Z 17.8N 54.6W 115 KT 130 MPH
36H 29/0600Z 18.8N 55.8W 115 KT 130 MPH
48H 29/1800Z 19.8N 57.3W 110 KT 125 MPH
60H 30/0600Z 21.2N 59.0W 110 KT 125 MPH
72H 30/1800Z 22.9N 60.5W 110 KT 125 MPH
96H 01/1800Z 27.8N 62.0W 105 KT 120 MPH
120H 02/1800Z 34.7N 59.6W 100 KT 115 MPH

$$
Forecaster Latto
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