ATL: THETA - Advisories

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ATL: THETA - Advisories

#1 Postby cycloneye » Mon Nov 09, 2020 10:00 pm

BULLETIN
Subtropical Storm Theta Advisory Number 1
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Tue Nov 10 2020

...SUBTROPICAL STORM FORMS OVER THE OPEN NORTHEAST ATLANTIC...
...RECORD-BREAKING 29TH NAMED STORM OF THE SEASON...


SUMMARY OF 300 AM GMT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...28.8N 40.3W
ABOUT 995 MI...1600 KM SW OF THE AZORES
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...E OR 90 DEGREES AT 15 MPH...24 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 300 AM GMT (0300 UTC), the center of Subtropical Storm Theta was
located near latitude 28.8 North, longitude 40.3 West. The storm is
moving toward the east near 15 mph (24 km/h), and a general
east-northeast motion is expected to continue during the next two to
three days.

Maximum sustained winds are near 50 mph (85 km/h) with higher gusts.
Some slight strengthening is possible during the next 12 to 24 hours
followed by little change in strength through Thursday.

Winds of 40 mph extend outward up to 115 miles (185 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 900 AM GMT.

$$
Forecaster Papin/Brown



Subtropical Storm Theta Discussion Number 1
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Tue Nov 10 2020

Over the past 12 h convection has slowly consolidated near the
center of a non-tropical area of low pressure over the far
northeast Atlantic. Earlier, there was a 2325 UTC ASCAT-B pass that
showed that the low-level circulation had become more detached
from the warm frontal boundary located to its northeast. In
addition, the ASCAT pass showed that winds have increased to near 45
kt on the southeast portion of the circulation near where coldest
convective cloud tops were located. Both a 2137 UTC SSMIS and 2324
UTC AMSU microwave pass showed convective banding under the cirrus
canopy near where the highest winds were observed. However, water
vapor satellite imagery still shows the presence of a broad
upper-level low tangled up with the low-level circulation embedded
in the convection. Therefore, Theta has been designated as a
subtropical storm with maximum wind of 45 kt.

Theta has been on a near due east heading over the last 12 h at
90/13 kt. Currently the cyclone is located south of a broad
deep-layer longwave trough. This trough is expected to bypass the
cyclone to the east and Theta will primarily be steered by
southwesterly flow on the northern periphery of a mid-level ridge
centered over the Cape Verde islands. This flow will steer Theta
slowly to the east-northeast over the next 3-5 days. The track
guidance is in good agreement with this solution, with only minor
differences in across-track spread. There are somewhat larger
differences in the along-track spread related to different forward
motion, but the latest NHC track forecast elected to stay close to
the track consensus at this time.

Theta’s structure has evolved from a frontal cyclone to a
subtropical cyclone, though a frontal boundary remains nearby on the
northeast side of the circulation. This boundary is expected to
gradually dissipate and Theta is expected to fully transition to a
tropical storm in 24 h as convection erodes the upper-level cyclonic
flow overhead. The maximum sustained winds were increased slightly
in the first 12 h of the forecast but are kept at 50 kt through 120
h which is on the high end of the intensity guidance.

Theta is the 29th named storm in the record-breaking 2020 Atlantic
Hurricane Season, breaking the previous record of 28th named storms
in 2005.


FORECAST POSITIONS AND MAX WINDS

INIT 10/0300Z 28.8N 40.3W 45 KT 50 MPH...SUBTROPICAL STORM
12H 10/1200Z 29.0N 38.6W 50 KT 60 MPH...SUBTROPICAL STORM
24H 11/0000Z 29.1N 36.3W 50 KT 60 MPH...TROPICAL STORM
36H 11/1200Z 29.5N 34.3W 50 KT 60 MPH
48H 12/0000Z 30.0N 32.6W 50 KT 60 MPH
60H 12/1200Z 30.5N 30.7W 50 KT 60 MPH
72H 13/0000Z 31.0N 28.7W 50 KT 60 MPH
96H 14/0000Z 32.2N 24.3W 50 KT 60 MPH
120H 15/0000Z 33.3N 20.6W 50 KT 60 MPH

$$
Forecaster Papin/Brown
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Re: ATL: THETA - Advisories

#2 Postby cycloneye » Tue Nov 10, 2020 5:14 am

Subtropical Storm Theta Discussion Number 2
NWS National Hurricane Center Miami FL AL302020
900 AM GMT Tue Nov 10 2020

Theta has generally changed little during the past several hours.
The cyclone has some characteristics of a tropical cyclone,
including a central dense overcast and a relatively small radius of
maximum wind. However, the storm is still entangled with an
upper-level trough, and based on all of these factors, Theta is
being maintained as a subtropical storm. The initial wind speed
remains 45 kt, which is at the high end of the satellite intensity
estimates.

The storm is moving due eastward at about 10 kt. The track
forecast reasoning seems fairly straightforward. A trough to the
north of the subtropical storm is expected to lift out, and Theta
should be steered eastward to east-northeastward during the next
several days on the north side of a mid-level ridge. This motion
should take the cyclone across the subtropical eastern Atlantic
throughout the forecast period. The models are in fairly good
agreement, and the NHC track forecast lies near the various
consensus aids.

Theta should transition to a tropical storm later today as it
separates from the upper-level trough. Little change in intensity
is expected during the next several days due to mixed environmental
conditions. Although Theta will be tracking over progressively
cooler SSTs and within moderate wind shear conditions, the air mass
is expected to remain unstable, which should be supportive of deep
convection. The NHC intensity forecast is similar to the previous
one and lies near the high end of the model guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 28.8N 39.5W 45 KT 50 MPH
12H 10/1800Z 28.9N 37.8W 50 KT 60 MPH
24H 11/0600Z 29.2N 35.7W 50 KT 60 MPH
36H 11/1800Z 29.7N 33.9W 50 KT 60 MPH
48H 12/0600Z 30.4N 31.6W 50 KT 60 MPH
60H 12/1800Z 31.0N 29.0W 50 KT 60 MPH
72H 13/0600Z 31.4N 26.7W 45 KT 50 MPH
96H 14/0600Z 32.2N 22.8W 45 KT 50 MPH
120H 15/0600Z 33.1N 19.9W 45 KT 50 MPH

$$
Forecaster Cangialosi
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Re: ATL: THETA - Advisories

#3 Postby cycloneye » Tue Nov 10, 2020 9:24 am

Subtropical Storm Theta Tropical Cyclone Update
NWS National Hurricane Center Miami FL AL302020
155 PM GMT Tue Nov 10 2020

...THETA STRONGER...

Recently received satellite wind data indicate that Theta has
strengthened and now has maximum sustained winds of around 70 mph
(110 km/h), with higher gusts. This change in intensity will be
reflected in the forecast that will be issued with the 300 PM GMT
(1500 UTC) advisory.


SUMMARY OF 155 PM GMT...1355 UTC...INFORMATION
----------------------------------------------
LOCATION...28.9N 37.6W
ABOUT 875 MI...1410 KM SW OF THE AZORES
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...E OR 85 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...989 MB...29.21 INCHES

$$
Forecaster Latto/Brennan
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Re: ATL: THETA - Advisories

#4 Postby cycloneye » Tue Nov 10, 2020 9:55 am

Subtropical Storm Theta Discussion Number 3
NWS National Hurricane Center Miami FL AL302020
300 PM GMT Tue Nov 10 2020

Theta continues to exhibit a mix of tropical and subtropical
characteristics. The cyclone has a fairly compact radius of maximum
winds with a central dense overcast over the northern portion of the
circulation. However, there is a strong subtropical jet located just
to the south of Theta, and strong upper-level winds in the
surrounding environment in the presence of an upper trough. Based on
this inconclusive data, Theta is being maintained as a subtropical
storm for this advisory. An ASCAT-B overpass this morning revealed
50-kt winds in the northwest and southwest quadrants, with several
55-60 kt wind vectors, some of those vectors outside of the deep
convection making them more believable. Based on this, the initial
advisory intensity has been set to 60 kt.

The storm is moving just north of due east, or 085/13 kt. Theta
should continue to be steered eastward to east-northeastward during
the next several days on the north side of a mid-level ridge. This
motion should take the cyclone across the subtropical eastern
Atlantic throughout the forecast period. The latest model guidance
is a little faster and slightly north of the previous forecast
track, and so the latest NHC forecast has been adjusted slightly as
well.

Theta is still expected to transition to a tropical storm later
today as it separates from the upper-level trough. Although Theta
will be tracking over progressively cooler SSTs and within moderate
wind shear conditions, the air mass is expected to remain unstable
for the next couple of days, which should be supportive of deep
convection. Therefore, little change is strength is indicated during
that time. Some weakening is anticipated later in the forecast
period as the airmass becomes more stable. The NHC intensity
forecast is higher than the previous one primarily due to the higher
initial intensity, and is near the IVCN and HCCA consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 29.0N 37.4W 60 KT 70 MPH
12H 11/0000Z 29.1N 35.7W 60 KT 70 MPH
24H 11/1200Z 29.7N 33.4W 60 KT 70 MPH
36H 12/0000Z 30.4N 31.3W 55 KT 65 MPH
48H 12/1200Z 31.1N 28.7W 55 KT 65 MPH
60H 13/0000Z 31.7N 26.0W 50 KT 60 MPH
72H 13/1200Z 32.2N 23.7W 45 KT 50 MPH
96H 14/1200Z 33.0N 19.5W 40 KT 45 MPH
120H 15/1200Z 34.3N 17.0W 35 KT 40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#5 Postby cycloneye » Tue Nov 10, 2020 3:40 pm

BULLETIN
Tropical Storm Theta Advisory Number 4
NWS National Hurricane Center Miami FL AL302020
900 PM GMT Tue Nov 10 2020

...THETA TRANSITIONS TO A TROPICAL CYCLONE OVER THE EASTERN
ATLANTIC...


SUMMARY OF 900 PM GMT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...29.4N 36.2W
ABOUT 795 MI...1280 KM SW OF THE AZORES
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...ENE OR 75 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...989 MB...29.21 INCHES


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


DISCUSSION AND OUTLOOK
----------------------
At 900 PM GMT (2100 UTC), the center of Tropical Storm Theta was
located near latitude 29.4 North, longitude 36.2 West. Theta is
moving toward the east-northeast near 14 mph (22 km/h) and this
motion is expected to continue for the next few days.

Maximum sustained winds are near 70 mph (110 km/h) with higher
gusts. Little change in strength is forecast during the next
couple of days. Some slow weakening is expected by later this week.

Tropical-storm-force winds extend outward up to 140 miles (220 km)
from the center.

The estimated minimum central pressure is 989 mb (29.21 inches).


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


NEXT ADVISORY
-------------
Next complete advisory at 300 AM GMT.

$$
Forecaster Latto



Tropical Storm Theta Discussion Number 4
NWS National Hurricane Center Miami FL AL302020
900 PM GMT Tue Nov 10 2020

A central dense overcast has persisted near the center of Theta
since yesterday, and although the clouds tops have warmed over the
past several hours there remains a distinct curved band feature
over the northern portion of the circulation. Water vapor imagery
shows the mid- upper-level trough that was over the Azores is
beginning to leave the cyclone behind. Based on these factors, and
the earlier indications of a compact radius of maximum winds, it
appears that Theta has completed a transition to a tropical
cyclone. Even though the clouds tops have recently warmed, the
overall structure of Theta has not degraded by much since the
previous advisory. Therefore, the initial intensity is being held
at 60 kt.

The storm is moving 075/12 kt around the north side of a mid-level
ridge. This feature should continue to steer Theta in a generally
east-northeastward motion for the next few days. Late in the
forecast period, the ridge will begin to weaken as another trough
approaches from the northwest. This should cause the cyclone to slow
its forward motion and begin to turn to the northeast. The latest
model guidance has once again slowed down and the new NHC track
forecast now lies between the previous one and the various consensus
models.

Although Theta will be moving over progressively cooler SSTs and
within moderate wind shear conditions, the air mass is expected to
remain unstable for the next day or so, which should be supportive
of deep convection. Therefore, little change is strength is
indicated during that time. Some weakening is anticipated later in
the forecast period as the airmass becomes more stable. By the end
of the 5-day forecast period, the combination of the cooler waters
and an approaching trough should result in extratropical transition.
The NHC intensity forecast has changed little from the previous one
and remains near the IVCN and HCCA consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 10/2100Z 29.4N 36.2W 60 KT 70 MPH
12H 11/0600Z 29.8N 34.7W 60 KT 70 MPH
24H 11/1800Z 30.3N 32.8W 55 KT 65 MPH
36H 12/0600Z 30.8N 30.5W 55 KT 65 MPH
48H 12/1800Z 31.5N 28.0W 50 KT 60 MPH
60H 13/0600Z 32.1N 25.7W 50 KT 60 MPH
72H 13/1800Z 32.6N 23.8W 45 KT 50 MPH
96H 14/1800Z 33.2N 20.5W 40 KT 45 MPH
120H 15/1800Z 34.4N 19.0W 35 KT 40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#6 Postby cycloneye » Tue Nov 10, 2020 9:48 pm

BULLETIN
Tropical Storm Theta Advisory Number 5
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Wed Nov 11 2020

...THETA MAINTAINING ITS INTENSITY AS IT MOVES OVER THE OPEN EASTERN
ATLANTIC...


SUMMARY OF 300 AM GMT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...29.4N 35.5W
ABOUT 770 MI...1235 KM SW OF THE AZORES
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...ENE OR 75 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...989 MB...29.21 INCHES


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


DISCUSSION AND OUTLOOK
----------------------
At 300 AM GMT (0300 UTC), the center of Tropical Storm Theta was
located near latitude 29.4 North, longitude 35.5 West. Theta is
moving toward the east-northeast near 12 mph (19 km/h) and this
motion is expected to continue for the next several days.

Maximum sustained winds are near 70 mph (110 km/h) with higher
gusts. Little change in strength is forecast during the next 72
hours.

Tropical-storm-force winds extend outward up to 205 miles (335 km)
from the center.

The estimated minimum central pressure is 989 mb (29.21 inches).


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


NEXT ADVISORY
-------------
Next complete advisory at 900 AM GMT.

$$
Forecaster Papin/Brown


Tropical Storm Theta Discussion Number 5
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Wed Nov 11 2020

Convection with Theta has waned some since the previous advisory,
with the coldest cloud tops now focused in a band on the
northeastern side of the partially exposed circulation. Despite this
decrease in convective coverage, a 2304 UTC ASCAT-B pass showed a
large region of 50 kt winds with at least one 55 kt barb.
Accounting for a bit of undersampling of this instrument and
maintaining continuity with the previous advisory, the maximum
sustained winds have been kept at 60 kt for this advisory.

Theta has slowed a bit tonight on the same east-northeast heading at
075/10 kt. The steering philosophy in the first part of the forecast
has remained the same, with Theta moving off to the east-northeast
while it continues to round the northern edge of a mid-level ridge
providing the steering flow. The latest track guidance has slowed
down the forward motion a bit more this cycle, and the new track
forecast splits the difference between the previous forecast and
some of the more reliable global model guidance that is slower and
south of the NHC track. At the end of the forecast period both the
ECMWF and GFS are forecasting Theta to become a shallow vortex as
the remaining convection is stripped away, and this could cause
Theta to slow down in the weaker low-level flow and move more
slowly to the northeast at the end of the forecast period.

Despite moving over gradually decreasing sea surface temperatures
over the next 48-72 h, upper-level temperatures are also forecast to
cool per GFS-SHIPS, which should provide enough instability for
moderate to deep convection. In addition, vertical wind shear may
decrease some in the 48-72 h period as Theta remains in light flow
along an upper-level trough axis. Therefore, the latest NHC
intensity forecast remains on the high end of the guidance for the
first three days, but now shows a faster weakening trend thereafter
as vertical wind shear increases out of the north and strips the
remaining convection away. At 5 days the forecast now makes Theta a
remnant low since it appears the circulation will be too shallow to
take advantage of more favorable baroclinic conditions that would
ordinarily allow for extratropical transition.

FORECAST POSITIONS AND MAX WINDS

INIT 11/0300Z 29.4N 35.5W 60 KT 70 MPH
12H 11/1200Z 29.7N 34.2W 60 KT 70 MPH
24H 12/0000Z 30.1N 32.5W 55 KT 65 MPH
36H 12/1200Z 30.5N 30.4W 55 KT 65 MPH
48H 13/0000Z 31.0N 27.7W 55 KT 65 MPH
60H 13/1200Z 31.7N 25.2W 55 KT 65 MPH
72H 14/0000Z 32.2N 23.2W 55 KT 65 MPH
96H 15/0000Z 32.8N 21.4W 50 KT 60 MPH
120H 16/0000Z 34.5N 20.1W 40 KT 45 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin/Brown
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Re: ATL: THETA - Advisories

#7 Postby cycloneye » Wed Nov 11, 2020 4:42 am

Tropical Storm Theta Discussion Number 6
NWS National Hurricane Center Miami FL AL302020
900 AM GMT Wed Nov 11 2020

Convection associated with Theta has decreased further this
morning, with strong southwesterly shear displacing the remaining
convection to the north of the center. Based on the decreased
organization, the initial intensity is lowered slightly to 55 kt.

Theta has continued to slow its forward speed, with the initial
motion now 075/7. The cyclone is being steered by the southern
part of the mid-latitude westerlies to the north of a mid-level
ridge, and this general motion should continue for the next 72 h or
so. After that time, the global models suggest that the cyclone
should shear apart, with the remnant low-level circulation moving
northeastward on the southeast side of a deep-layer cyclone over
the northeastern Atlantic. There has been little change in the
guidance since the previous advisory, and the new official forecast
track is similar to the previous track.

While the cyclone is currently experiencing strong shear, the
global models show that this might diminish somewhat during the
next 72 h as Theta moves into an area of light winds near an
upper-level trough axis. This, combined with sufficient
instability for deep convection, should allow the storm to change
little in strength during this time. After 72 h, strong mid- to
upper-level northerly flow should cause the system to weaken as the
convection dissipates and the upper-level portion of the storm is
pushed off to the south. The new intensity forecast is lowered a
bit from the previous forecast, and it lies in the middle of the
intensity guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 11/0900Z 29.4N 34.7W 55 KT 65 MPH
12H 11/1800Z 29.9N 33.5W 55 KT 65 MPH
24H 12/0600Z 30.4N 31.5W 55 KT 65 MPH
36H 12/1800Z 30.8N 29.1W 50 KT 60 MPH
48H 13/0600Z 31.3N 26.7W 50 KT 60 MPH
60H 13/1800Z 31.8N 24.4W 50 KT 60 MPH
72H 14/0600Z 32.1N 23.1W 50 KT 60 MPH
96H 15/0600Z 32.5N 21.5W 45 KT 50 MPH
120H 16/0600Z 34.0N 20.0W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Beven
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Re: ATL: THETA - Advisories

#8 Postby cycloneye » Wed Nov 11, 2020 11:08 am

Tropical Storm Theta Discussion Number 7
NWS National Hurricane Center Miami FL AL302020
300 PM GMT Wed Nov 11 2020

Theta's center continues to be devoid of deep convection, with the
convective mass located primarily to the north of the center due to
strong shear. A recent partial ASCAT overpass showed a slight
decrease in the winds over the eastern semicircle. However, the pass
did not sample the western portion of the circulation which has
previously had the strongest winds. Based on the slightly lower
ASCAT values, and the assumption that the rest of the vortex has
spun down slightly due to the lack of convection over the center,
the initial intensity is decreased to 50 kt.

Theta is moving east-northeastward at 9 kt, steered by the southern
part of the mid-latitude westerlies to the north of a mid-level
ridge. This steering pattern is expected to remain in place through
much of the weekend. By early next week, the ridge is forecast
weaken ahead of an approaching mid-latitude trough. This would cause
the cyclone to slow its forward motion temporarily before it gets
picked up by the trough. The latest NHC forecast is near the
previous one through 72 h, and is a little slower during days 4-5
due to the slowing of the guidance. This latest forecast is very
near the clustered track consensus models.

Despite the strong shear and cool water temperatures, the
instability aloft should continue to support deep convection for at
least the next few days. The shear is forecast to lessen somewhat
in a day or so, but will still be relatively strong. Since the
cyclone has been weakening slowly in the current environment, it is
anticipated that the pace of weakening may lessen during the next
few days with the decrease in shear. Beyond that time, the
upper-level winds are forecast to become more northerly, and
at about the same time the instability is forecast to decrease.
These factors should cause any remaining convection to dissipate,
with Theta likely becoming post-tropical by day 5. The latest
NHC intensity forecast was adjusted slightly downward from the
previous one mainly due to the lower initial intensity and is near
the IVCN and HCCA consensus model forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT 11/1500Z 29.8N 33.3W 50 KT 60 MPH
12H 12/0000Z 30.3N 31.9W 50 KT 60 MPH
24H 12/1200Z 30.7N 29.7W 45 KT 50 MPH
36H 13/0000Z 31.1N 27.3W 45 KT 50 MPH
48H 13/1200Z 31.5N 25.1W 45 KT 50 MPH
60H 14/0000Z 31.8N 23.2W 45 KT 50 MPH
72H 14/1200Z 31.9N 22.0W 40 KT 45 MPH
96H 15/1200Z 32.2N 20.6W 35 KT 40 MPH
120H 16/1200Z 34.7N 19.2W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#9 Postby cycloneye » Wed Nov 11, 2020 3:50 pm

Tropical Storm Theta Discussion Number 7
NWS National Hurricane Center Miami FL AL302020
300 PM GMT Wed Nov 11 2020

Theta's center continues to be devoid of deep convection, with the
convective mass located primarily to the north of the center due to
strong shear. A recent partial ASCAT overpass showed a slight
decrease in the winds over the eastern semicircle. However, the pass
did not sample the western portion of the circulation which has
previously had the strongest winds. Based on the slightly lower
ASCAT values, and the assumption that the rest of the vortex has
spun down slightly due to the lack of convection over the center,
the initial intensity is decreased to 50 kt.

Theta is moving east-northeastward at 9 kt, steered by the southern
part of the mid-latitude westerlies to the north of a mid-level
ridge. This steering pattern is expected to remain in place through
much of the weekend. By early next week, the ridge is forecast
weaken ahead of an approaching mid-latitude trough. This would cause
the cyclone to slow its forward motion temporarily before it gets
picked up by the trough. The latest NHC forecast is near the
previous one through 72 h, and is a little slower during days 4-5
due to the slowing of the guidance. This latest forecast is very
near the clustered track consensus models.

Despite the strong shear and cool water temperatures, the
instability aloft should continue to support deep convection for at
least the next few days. The shear is forecast to lessen somewhat
in a day or so, but will still be relatively strong. Since the
cyclone has been weakening slowly in the current environment, it is
anticipated that the pace of weakening may lessen during the next
few days with the decrease in shear. Beyond that time, the
upper-level winds are forecast to become more northerly, and
at about the same time the instability is forecast to decrease.
These factors should cause any remaining convection to dissipate,
with Theta likely becoming post-tropical by day 5. The latest
NHC intensity forecast was adjusted slightly downward from the
previous one mainly due to the lower initial intensity and is near
the IVCN and HCCA consensus model forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT 11/1500Z 29.8N 33.3W 50 KT 60 MPH
12H 12/0000Z 30.3N 31.9W 50 KT 60 MPH
24H 12/1200Z 30.7N 29.7W 45 KT 50 MPH
36H 13/0000Z 31.1N 27.3W 45 KT 50 MPH
48H 13/1200Z 31.5N 25.1W 45 KT 50 MPH
60H 14/0000Z 31.8N 23.2W 45 KT 50 MPH
72H 14/1200Z 31.9N 22.0W 40 KT 45 MPH
96H 15/1200Z 32.2N 20.6W 35 KT 40 MPH
120H 16/1200Z 34.7N 19.2W 35 KT 40 MPH...POST-TROPICAL

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#10 Postby cycloneye » Wed Nov 11, 2020 10:04 pm

Tropical Storm Theta Discussion Number 9
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Thu Nov 12 2020

The cloud appearance of Theta briefly became a bit more symmetric
earlier tonight, though the colder cloud tops that attempted to wrap
around the low-level center have recently decayed, possibly due to
entrainment of dry mid-latitude air. A 2243 UTC ASCAT-B pass
and a subsequent ASCAT-C pass both found the max winds with Theta
a little stronger than previously estimated with maximum values
exceeding 50 kt. These data support an initial intensity of 55 kt,
and this could even be a little conservative.

Over the last 6 h Theta appears to have made a slight jog left of
the previous forecast track, perhaps related to the convection
wrapping around the center, but the longer term motion is still
east-northeast at about 10 kt. Over the next day, Theta is expected
to continue to move east-northeastward as it rounds the north side
of a mid-level ridge centered over the Cape Verde islands. Between
48 h to 72 h Theta's track is forecast to bend east and then
east-southeast as the mid-level ridge to the south weakens a bit,
and mid to upper-level northerly flow from a weak mid-level ridge
attempts to build in to the west. The latest track guidance shows a
fair amount of spread in how quickly Theta makes this bend to the
east-southeast, and this is a large source of uncertainty in the
forecast. The NHC track forecast splits the difference between the
faster ECMWF and slower HMON/HWRF guidance, and is not far from the
TVCN consensus.

The intensity forecast of Theta has been adjusted upward for the
first 48 h due to the higher initial intensity. GFS-SHIPS
diagnostics indicate the vertical wind shear will gradually
decrease while Theta moves through an unstable temperature profile
conducive for moderate to deep convection. Thereafter, the
aforementioned upper-level northerly flow will lead to an increase
in the vertical wind shear and import very stable mid-latitude air
over Thetas circulation. Most of the reliable global model
guidance shows Theta succumbing to these negative effects and
becoming a remnant low by 96 h. The official intensity forecast
shows the same, and is on the high side of the guidance but not far
from any of the models since the spread is quite low.

FORECAST POSITIONS AND MAX WINDS

INIT 12/0300Z 31.1N 31.4W 55 KT 65 MPH
12H 12/1200Z 31.5N 29.8W 55 KT 65 MPH
24H 13/0000Z 32.0N 27.8W 55 KT 65 MPH
36H 13/1200Z 32.1N 25.4W 55 KT 65 MPH
48H 14/0000Z 31.8N 23.4W 50 KT 60 MPH
60H 14/1200Z 31.4N 21.9W 45 KT 50 MPH
72H 15/0000Z 31.2N 20.5W 40 KT 45 MPH
96H 16/0000Z 31.2N 19.8W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 17/0000Z 35.6N 18.9W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin/Zelinsky
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Re: ATL: THETA - Advisories

#11 Postby cycloneye » Thu Nov 12, 2020 4:29 am

Tropical Storm Theta Discussion Number 10
NWS National Hurricane Center Miami FL AL302020
900 AM GMT Thu Nov 12 2020

Theta currently is comprised of a large swirl of low- to mid-level
clouds with no convection near the center. However, a band of
convection is wrapped about three-quarters of the way around the
center at a distance of about 200 n mi in the eastern semicircle
and 100 n mi in the western semicircle. Overall, the cyclone has
somewhat of a subtropical appearance at this time. Since there
has been no data from the cyclone's core region since the last
scatterometer pass, the initial intensity is held at 55 kt.

The storm continued to jog a little to the left since the last
advisory, but the last few satellite images suggest a more eastward
motion has resumed. The initial motion is a somewhat uncertain
060/10. For the next 24 h or so, Theta is expected to continue to
move east-northeastward as it rounds the north side of a mid-level
ridge centered over the Cabo Verde islands. An eastward to
east-southeastward motion is expected from 24-72 h as the mid-level
ridge to the south weakens and mid- to upper-level northerly flow
moves over the cyclone. After that time, Theta or its remnants is
expected to be steered northeastward in the low-level flow to the
southeast of a deep-layer mid-latitude cyclone over the
northeastern Atlantic. The new forecast track is adjusted north of
the previous track based on the initial position and motion, and it
lies near the various consensus models.

Theta is forecast to change little in intensity during the next 36
h or so as it moves into the light shear area near an upper-level
trough axis. After that time, the trough moves south of the
cyclone, and strong northerly vertical shear should occur along
with the entrainment of stable air. This combination should cause
Theta to quickly weaken, and the intensity forecast calls for the
system to decay to a remnant low pressure area by 96 h. The new
intensity forecast has only minor adjustments from the old
forecast, and it lies a little above the intensity consensus.


FORECAST POSITIONS AND MAX WINDS

INIT 12/0900Z 31.7N 30.2W 55 KT 65 MPH
12H 12/1800Z 32.0N 28.5W 55 KT 65 MPH
24H 13/0600Z 32.3N 26.2W 55 KT 65 MPH
36H 13/1800Z 32.3N 24.0W 55 KT 65 MPH
48H 14/0600Z 32.0N 22.1W 50 KT 60 MPH
60H 14/1800Z 31.7N 20.8W 40 KT 45 MPH
72H 15/0600Z 31.6N 20.1W 35 KT 40 MPH
96H 16/0600Z 33.0N 19.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 17/0600Z 37.0N 18.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven
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Re: ATL: THETA - Advisories

#12 Postby cycloneye » Thu Nov 12, 2020 10:23 am

Tropical Storm Theta Discussion Number 11
NWS National Hurricane Center Miami FL AL302020
300 PM GMT Thu Nov 12 2020

Although the cloud top temperatures across the broad comma-shaped
convective shield have warmed this morning, there is some new
convection that has been developing nearer to Theta's center over
the past few hours. Unfortunately, the scatterometer passes this
morning missed sampling the winds near the center of the cyclone.
However, the partial ASCAT-A overpass showed that 45 kt winds are
occurring nearly 100 n mi to the southwest of the center of Theta.
Therefore it is assumed that stronger winds are still occurring
closer to the center of the cyclone, and the initial intensity is
being held at 55 kt.

Theta has now turned to the right, and the initial motion is 080/10
kt. For about the next 36 h, the cyclone is expected to continue
moving just north of east around the north side of a mid-level
ridge. A slower east-southeastward motion is expected from 36-72 h
as the mid-level ridge to the south weakens and mid- to upper-level
northerly flow moves over Theta. After 72 h, Theta or its
remnants are expected to turn northeastward or northward and
accelerate in the low-level flow ahead of an approaching deep-layer
mid-latitude cyclone over the northeastern Atlantic. The latest
track forecast is little changed from the previous one and is near
the multi-model consensus tracks.

The shear across Theta is expected to relax somewhat over the day or
so, while moving over cooler waters. The counteracting effects
should allow the cyclone to maintain its intensity. By this weekend,
strong northerly shear is expected to impact Theta, while stable air
gets entrained into its circulation. This should cause the cyclone
to weaken, with the system likely degenerating into a remnant low by
Sunday. The latest NHC intensity forecast is just slightly above the
guidance through 60 h, and is near the various consensus models
thereafter.


FORECAST POSITIONS AND MAX WINDS

INIT 12/1500Z 31.6N 28.8W 55 KT 65 MPH
12H 13/0000Z 31.7N 27.0W 55 KT 65 MPH
24H 13/1200Z 31.8N 24.7W 55 KT 65 MPH
36H 14/0000Z 31.8N 22.6W 55 KT 65 MPH
48H 14/1200Z 31.5N 21.0W 50 KT 60 MPH
60H 15/0000Z 31.2N 20.2W 40 KT 45 MPH
72H 15/1200Z 31.1N 19.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 16/1200Z 32.7N 19.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 17/1200Z 37.6N 17.4W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#13 Postby cycloneye » Thu Nov 12, 2020 3:51 pm

Tropical Storm Theta Discussion Number 12
NWS National Hurricane Center Miami FL AL302020
900 PM GMT Thu Nov 12 2020

The appearance and structure of Theta has changed little today, with
intermittent bursts of convection wrapping mostly around the center
of circulation. There has been no new observational data since last
night, and it is still assumed that the cyclone's intensity remains
a somewhat uncertain 55 kt due to the consistency of its
appearance.

Theta's motion over the past 12 h is 090/10 kt as the cyclone
continues to be steered around the north side of a mid-level ridge.
A slower east-southeastward motion is expected from 36-72 h as the
mid-level ridge to the south weakens and mid- to upper-level
northerly flow moves over Theta. After 72 h, Theta or its remnants
are expected to turn northeastward or northward and accelerate in
the low-level flow ahead of an approaching mid-latitude cyclone over
the northeastern Atlantic. The latest track forecast has changed
little from the previous one and remains near the multi-model
consensus tracks.

The shear across Theta is expected to relax somewhat over the next
day or so, while the cyclone moves over cooler waters. These
counteracting effects should allow the cyclone to maintain its
intensity during that time. By this weekend, strong northerly shear
is expected to impact Theta, while stable air gets entrained into
its circulation. This should cause the cyclone to weaken, with the
system likely degenerating into a remnant low by Sunday. The latest
NHC intensity forecast is essentially unchanged from the previous
one and is close to the various consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 12/2100Z 31.7N 27.4W 55 KT 65 MPH
12H 13/0600Z 31.8N 25.7W 55 KT 65 MPH
24H 13/1800Z 31.8N 23.4W 55 KT 65 MPH
36H 14/0600Z 31.5N 21.5W 55 KT 65 MPH
48H 14/1800Z 31.2N 20.2W 45 KT 50 MPH
60H 15/0600Z 31.1N 19.4W 35 KT 40 MPH
72H 15/1800Z 31.4N 19.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 16/1800Z 34.0N 19.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 17/1800Z 38.4N 15.4W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#14 Postby cycloneye » Thu Nov 12, 2020 9:53 pm

Tropical Storm Theta Discussion Number 13
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Fri Nov 13 2020

The structure of Theta has been waxing and waning today with
moderate convection attempting to wrap around the center, though the
coldest cloud tops have been decaying before wrapping fully around.
Earlier, there was a 2222 UTC partial ASCAT-B pass that showed peak
winds of 40-45 kt on the south side of Theta. However the highest
winds from this instrument the previous two nights were in the
southwest quadrant and it is estimated that higher winds may still
exist in this quadrant of Theta. For this reason, the latest
intensity estimate is only adjusted downward to 50 kt for this
advisory.

Theta continues to track east at 090/12 kt as the system remains
steered by flow along the north side of a mid-level ridge. This
ridge is forecast to gradually weaken over the next 24-36 h and
Theta is forecast to bend to the east-southeast as the cyclone
becomes more influenced by mid-level northerly flow associated with
an upstream ridge building to the northwest. After 36 h, Theta is
expected to slow down significantly as it becomes a shallow cyclone
in light low-level flow. Finally, low-level southerly flow ahead of
a mid-latitude cyclone is forecast to steer Theta's remnant low
northeastward by the end of the forecast. The track guidance this
cycle has shifted a bit southward for the first part of the
forecast, and the official NHC track forecast has been adjusted
slightly further south, close to the reliable ICVN consensus.

Thus far, Theta has been struggling to produce deep convection that
has successfully wrapped around its center. While Vertical Wind
Shear is forecast to decrease per ECMWF-SHIPS guidance over the next
12-24 h, it remains to be seen if the current degree of instability
is enough for Theta to take advantage of the more conducive wind
environment. Thereafter, Vertical Wind Shear increases sharply from
the north, importing a much more stable environment over Theta. For
now, the latest NHC intensity forecast maintains the current 50 kt
intensity over the next 24 h with weakening forecasted thereafter,
in general agreement with the latest intensity guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 13/0300Z 31.7N 26.0W 50 KT 60 MPH
12H 13/1200Z 31.7N 24.2W 50 KT 60 MPH
24H 14/0000Z 31.4N 22.1W 50 KT 60 MPH
36H 14/1200Z 31.0N 20.4W 45 KT 50 MPH
48H 15/0000Z 30.8N 19.2W 40 KT 45 MPH
60H 15/1200Z 30.8N 18.6W 30 KT 35 MPH
72H 16/0000Z 31.2N 18.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 17/0000Z 34.3N 18.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 18/0000Z...DISSIPATED

$$
Forecaster Papin/Cangialosi
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Re: ATL: THETA - Advisories

#15 Postby cycloneye » Fri Nov 13, 2020 6:19 am

Tropical Storm Theta Discussion Number 14
NWS National Hurricane Center Miami FL AL302020
900 AM GMT Fri Nov 13 2020

A fortuitous 0348 UTC AMSR2 microwave pass revealed that Theta's
surface center was a little to the north of the previous advisory
position. The image also indicated that the coldest brightness
temperatures were located in the northeast quadrant which sort of
conflicts with the earlier scatterometer data showing the stronger
surface winds in the southeast quadrant. More than likely though,
these winds are being produced by the pressure gradient of the
cyclone and a mid-level ridge to the southeast. Since the cloud
pattern has changed little during the past several hours and the
subjective satellite intensity estimate from TAFB hasn't either,
the initial intensity is held at 50 kt for this advisory.

Theta is forecast to change little in intensity during the next 12
hours or so as the cyclone continues moving in a low shear zone
associated with a mid- to upper-level trough axis. On Saturday,
the trough migrates south of Theta, while strong northerly shear
and a more stable air mass intrude from the northwest to north. As
a result, Theta is expected to spin down and degenerate to a
remnant low on Sunday and dissipate by mid next week.

Theta has been moving eastward during the last 12 hours within the
mid-level troposphere steering current provided by a mid-level
ridge extending westward from west Africa to the eastern tropical
Atlantic. The short term motion, however, already appears to be
the anticipated to the right of track motion, or toward the
east-southeast. Regardless, this general motion along with a
reduction in forward speed is forecast during the next couple of
days as a more vertically shallow Theta is influenced by the
low-level flow. By day 3, the remnants of Theta are expected to
turn rather sharply northward and continue in this general motion
in response to an approaching deep-layer mid-latitude cyclone from
the northeastern Atlantic. The NHC forecast is similar to the
previous one through the 72 hour period, then adjusted to the right
to align more with the various consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 13/0900Z 31.9N 24.9W 50 KT 60 MPH
12H 13/1800Z 31.7N 23.3W 50 KT 60 MPH
24H 14/0600Z 31.4N 21.3W 45 KT 50 MPH
36H 14/1800Z 31.1N 19.7W 45 KT 50 MPH
48H 15/0600Z 30.9N 18.5W 40 KT 45 MPH
60H 15/1800Z 31.1N 18.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 16/0600Z 32.1N 18.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 17/0600Z 36.0N 17.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 18/0600Z...DISSIPATED

$$
Forecaster Roberts
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Re: ATL: THETA - Advisories

#16 Postby cycloneye » Fri Nov 13, 2020 10:25 am

Tropical Storm Theta Discussion Number 15
NWS National Hurricane Center Miami FL AL302020
300 PM GMT Fri Nov 13 2020

Satellite images and microwave data this morning are showing that
Theta finally has a more classic appearance of a tropical storm.
There is a warming of cloud tops over the center, with a curved band
of convection wrapping around the eastern portion of the
circulation. The scatterometer overpasses missed the core of the
cyclone this morning. However, since the cloud pattern has not
degraded since the previous advisory, the intensity is being held at
50 kt for this advisory.

Theta is forecast to change little in intensity today as the cyclone
continues moving in a low shear zone associated with a mid- to
upper-level trough axis. By tomorrow, strong northerly shear is
forecast to begin impacting the system while stable air gets
entrained into its circulation. As a result, Theta is expected to
spin down over the weekend, degenerate to a remnant low on Sunday,
and dissipate by the middle of next week.

Theta continues to move eastward at around 10 kt, steered by a
mid-level ridge extending westward from west Africa to the eastern
tropical Atlantic. A turn to the east-southeast along with a gradual
slowing of the forward motion is expected later today and
continuing through the weekend as the ridge weakens, and mid-
to upper level northerly winds impart on the cyclone. Early next
week, what remains of Theta are expected to turn northward and then
accelerate northeastward as a mid-latitude cyclone passes to the
north of the region. The NHC forecast is little changed from the
previous one and lies near the various consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 13/1500Z 31.7N 23.8W 50 KT 60 MPH
12H 14/0000Z 31.5N 22.2W 50 KT 60 MPH
24H 14/1200Z 31.3N 20.4W 45 KT 50 MPH
36H 15/0000Z 31.0N 19.1W 45 KT 50 MPH
48H 15/1200Z 31.1N 18.3W 35 KT 40 MPH
60H 16/0000Z 31.3N 18.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 16/1200Z 32.8N 18.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 17/1200Z 37.4N 15.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 18/1200Z...DISSIPATED

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#17 Postby cycloneye » Fri Nov 13, 2020 3:39 pm

Tropical Storm Theta Discussion Number 16
NWS National Hurricane Center Miami FL AL302020
900 PM GMT Fri Nov 13 2020

Theta appears to be holding its own still, with a large curved band
feature characterizing the bulk of the deep convection, and a
smaller area of convection intermittently developing over the
center. Like yesterday, there has been a lack of observational data
over the system's core since last night. However, since Theta's
organization has not appeared to change much since that time, the
initial intensity is being kept at a somewhat uncertain 50 kt.

Theta is forecast to change little in intensity into tonight as the
cyclone continues moving in a relatively low shear zone associated
with a mid- to upper-level trough axis. By tomorrow, strong
northerly shear is forecast to begin impacting the system while
stable air gets entrained into its circulation. As a result, Theta
is expected to spin down over the weekend, degenerate to a remnant
low on Sunday, and dissipate by the middle of next week.

Theta is moving eastward at around 9 kt, steered by a mid-level
ridge extending westward from west Africa to the eastern tropical
Atlantic. A turn to the east-southeast along with a gradual slowing
of the forward motion is expected overnight and continuing through
the weekend as the ridge weakens, and mid- to upper level northerly
winds impart on the cyclone. Early next week, what remains of Theta
are expected to turn northward and then accelerate northeastward as
a mid-latitude cyclone passes to the north of the region. The NHC
forecast is little changed from the previous one and lies near the
various consensus aids. On the forecast track, the center of Theta
is forecast to track very near the westernmost Canary Islands.
However, the system is forecast to weaken to a remnant low before
reaching those islands.


FORECAST POSITIONS AND MAX WINDS

INIT 13/2100Z 31.9N 22.6W 50 KT 60 MPH
12H 14/0600Z 31.7N 21.0W 50 KT 60 MPH
24H 14/1800Z 31.4N 19.2W 45 KT 50 MPH
36H 15/0600Z 31.3N 18.2W 40 KT 45 MPH
48H 15/1800Z 31.7N 17.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
60H 16/0600Z 32.5N 17.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 16/1800Z 34.4N 17.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 17/1800Z 39.2N 12.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 18/1800Z...DISSIPATED

$$
Forecaster Latto
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Re: ATL: THETA - Advisories

#18 Postby cycloneye » Fri Nov 13, 2020 9:47 pm

Tropical Storm Theta Discussion Number 17
NWS National Hurricane Center Miami FL AL302020
300 AM GMT Sat Nov 14 2020

Theta is beginning to show signs of weakening tonight. Infrared
cloud top temperatures have warmed during the past several hours
within the weakening convective band that curves around the
northeastern semicircle of the storm. A partial 22 UTC ASCAT-B
overpass indicates that Theta maintains a fairly symmetric low-level
wind field, with 35-40 kt winds in the eastern semicircle of the
storm. Therefore, the initial intensity is lowered to 45 kt with
this advisory, which is consistent with UW-CIMSS objective current
intensity estimates but slightly higher than the T2.5 subjective
Dvorak classification from TAFB.

Theta will encounter increasingly hostile environmental conditions
over the next couple of days. The NHC intensity forecast calls for
steady weakening through the weekend, as strong northerly wind shear
and cool sea surface temperatures will likely inhibit the storm from
sustaining convection near its center. This forecast closely follows
the corrected consensus aid HCCA. Theta is expected to weaken to a
tropical depression within 36 h and degenerate into a remnant low by
48 h, although the GFS simulated satellite imagery suggests this
could occur even sooner than forecast. The remnant low should
dissipate by the middle of next week.

Theta is still moving eastward at around 9 kt around the northern
periphery of a mid-level ridge that extends from western Africa
across the eastern tropical Atlantic. An eastward or
east-southeastward motion with a gradual decrease in forward speed
is expected during the next 24-36 h. As the storm spins down and
becomes a more shallow circulation, the remains of Theta will turn
northward and then accelerate northeastward ahead of a mid-latitude
cyclone and associated frontal system that will cross the
northeastern Atlantic. The NHC track forecast lies close to the
previous one and near the center of the guidance envelope. On the
forecast track, the center of Theta is expected to pass northwest of
the Canary Islands this weekend, then move near Madeira Island early
Monday as a weak remnant low.


FORECAST POSITIONS AND MAX WINDS

INIT 14/0300Z 31.9N 21.6W 45 KT 50 MPH
12H 14/1200Z 31.8N 20.2W 40 KT 45 MPH
24H 15/0000Z 31.6N 18.6W 35 KT 40 MPH
36H 15/1200Z 31.7N 17.8W 30 KT 35 MPH
48H 16/0000Z 32.3N 17.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
60H 16/1200Z 33.7N 17.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 17/0000Z 35.9N 16.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 18/0000Z...DISSIPATED

$$
Forecaster Reinhart/Cangialosi
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Re: ATL: THETA - Advisories

#19 Postby cycloneye » Sat Nov 14, 2020 5:07 am

Tropical Storm Theta Discussion Number 18
NWS National Hurricane Center Miami FL AL302020
900 AM GMT Sat Nov 14 2020

Nearly all of the deep convection associated with Theta has
dissipated since the previous advisory, with only cold, high cirrus
clouds remaining in the northeastern quadrant. A late-arriving
13/2255Z partial ASCAT-C pass indicated a few 35-kt wind vectors
were present in the southeastern quadrant, so the initial intensity
has been lowered to 35 kt for this advisory, which is consistent
the latest TAFB current intensity estimate of T2.5/35 kt.

The initial motion estimate is due east, or 090/08 kt. Theta is
expected to move eastward along the northern periphery of a
deep-layer ridge for the next 24 hours or so, a motion that will
also be accompanied by a gradual decrease in forward speed. By 36
hours, a much weaker and more vertically shallow Theta is forecast
to turn sharply northward ahead of a frontal system. In the 48-72
hour period, the weakening cyclone expected to accelerate
northeastward ahead of the front, passing to the north of the
Canary Islands this weekend. Theta is forecast to dissipate by 96
hours near the Madeira Island. The new NHC track forecast is similar
to the previous advisory, and lies close to the consensus model
TVCN.

Strong shear in excess of 35 kt currently affecting Theta is
forecast to steadily increase to more than 40 kt by 12 h and beyond.
In addition, entrainment of very dry mid-level air should combine
with the increasing shear and prevent the reformation of persistent
organized deep convection near the center. Although the global
models show that some marginal instability is expected to linger
through the forecast period, only intermittent small bursts of
modest convection away from the center could develop. However, the
general trend in the model guidance calls for Theta to slowly spin
down, and the official intensity forecast follows that scenario,
calling for the cyclone to weaken to a remnant low later today, then
becoming extratropical before dissipating in 3-4 days.

FORECAST POSITIONS AND MAX WINDS

INIT 14/0900Z 32.0N 20.8W 35 KT 40 MPH
12H 14/1800Z 31.8N 19.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
24H 15/0600Z 31.8N 18.3W 30 KT 35 MPH...POST-TROP/EXTRATROP
36H 15/1800Z 32.2N 17.7W 25 KT 30 MPH...POST-TROP/EXTRATROP
48H 16/0600Z 33.2N 17.4W 20 KT 25 MPH...POST-TROP/EXTRATROP
60H 16/1800Z 34.9N 16.6W 20 KT 25 MPH...POST-TROP/EXTRATROP
72H 17/0600Z 37.2N 15.6W 20 KT 25 MPH...POST-TROP/EXTRATROP
96H 18/0600Z...DISSIPATED

$$
Forecaster Stewart
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cycloneye
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Re: ATL: THETA - Advisories

#20 Postby cycloneye » Sat Nov 14, 2020 10:01 am

Tropical Storm Theta Discussion Number 19
NWS National Hurricane Center Miami FL AL302020
300 PM GMT Sat Nov 14 2020

Theta's center continues to be devoid of deep convection as dry air
entrains into the system's circulation. The edge of the only nearby
surviving convection is located about 60 n mi to the southeast of
the cyclone's center due to increasing northwesterly shear. A recent
ASCAT overpass showed a fair amount of wind vectors of 30-34 kt,
therefore the initial intensity remains 35 kt for this advisory. The
shear is expected to increase even more today, and the surrounding
environment is forecast to dry out further. These factors, that
should persist for at least the next few days, should prevent any
new convection from developing near the center of Theta. The latest
NHC forecast calls for the system to become a remnant low in 12 h
and dissipate in 72 h, as the circulation gradually spins down.

The storm is now moving just south of due east around 7 kt as it is
steered along the northern periphery of a mid-level ridge. This
ridge is forecast to weaken over the next couple of days, which will
cause Theta to slow its forward motion. Early next week, increasing
southerly flow ahead of an approaching cold front should pick up
the remnants of Theta and accelerate them northward, and then
northeastward. The latest NHC track forecast is similar to the
previous one and lies near the track consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 14/1500Z 31.8N 20.2W 35 KT 40 MPH
12H 15/0000Z 31.6N 19.1W 35 KT 40 MPH...POST-TROP/REMNT LOW
24H 15/1200Z 31.7N 18.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 16/0000Z 32.4N 17.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 16/1200Z 33.7N 17.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
60H 17/0000Z 36.1N 16.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 17/1200Z...DISSIPATED

$$
Forecaster Latto
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