ATL: GERT - Advisories

[cycloneye]

BULLETIN
Tropical Depression Gert Advisory Number 14
NWS National Hurricane Center Miami FL AL062023
500 AM AST Fri Sep 01 2023

...GERT REGENERATES INTO A TROPICAL DEPRESSION...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...28.7N 55.0W
ABOUT 635 MI...1020 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...E OR 90 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES




Tropical Depression Gert Discussion Number 14
NWS National Hurricane Center Miami FL AL062023
500 AM AST Fri Sep 01 2023

After more than a week of meandering over the central Atlantic, the
circulation of former Tropical Storm Gert has again become well
defined, and the system has acquired enough persistent and
organized deep convection for it to be classified as a tropical
depression once again. A recent AMSR2 microwave overpass shows that
the small circulation is located near the northeastern portion of
the persistent convective mass. The initial intensity is set at 30
kt and is based on the latest subjective Dvorak estimates from TAFB
and SAB.

Gert is located within an area of moderate to strong shear. The
shear is forecast to increase even more in the next 18-24 hours
which should limit strengthening, however Gert could re-gain
tropical storm status today. Over the weekend, gradual weakening
is expected when the upper-level environment becomes more hostile.
The global models are in relatively good agreement that Gert will
be absorbed by the larger circulation of Idalia when it is over the
central Atlantic in 3 to 4 days.

Gert is moving eastward at about 7 kt. The eastward motion should
continue today, but by Saturday, Gert is forecast to turn
northeastward as it is steered around the low- to mid-level flow
around the eastern side of the larger circulation of Idalia. By 48
hours Gert should turn northward around the eastern flank of Idalia
and that motion should continue until dissipation occurs. The
track guidance is in good agreement on the overall scenario but
there are significant differences in Gert's forward speed. The NHC
track is a blend of the GFS and ECMWF models.


FORECAST POSITIONS AND MAX WINDS

INIT 01/0900Z 28.7N 55.0W 30 KT 35 MPH
12H 01/1800Z 28.7N 54.0W 35 KT 40 MPH
24H 02/0600Z 29.1N 53.1W 35 KT 40 MPH
36H 02/1800Z 29.7N 52.6W 30 KT 35 MPH
48H 03/0600Z 30.7N 52.2W 30 KT 35 MPH
60H 03/1800Z 32.3N 51.8W 30 KT 35 MPH
72H 04/0600Z 34.7N 51.7W 25 KT 30 MPH
96H 05/0600Z...DISSIPATED

$$
Forecaster Brown

[cycloneye]

BULLETIN
Tropical Depression Gert Advisory Number 15
NWS National Hurricane Center Miami FL AL062023
1100 AM AST Fri Sep 01 2023

...GERT COULD BECOME A TROPICAL STORM AGAIN TODAY AFTER 11 DAYS...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...28.7N 54.6W
ABOUT 655 MI...1055 KM ESE OF BERMUDA
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...E OR 90 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES




Tropical Depression Gert Discussion Number 15
NWS National Hurricane Center Miami FL AL062023
1100 AM AST Fri Sep 01 2023

Gert's structure hasn't changed much since it regenerated, and it
remains strongly sheared from the north. ASCAT is not expected to
sample Gert this morning, so the 30-kt intensity is based entirely
on a blend of Dvorak estimates from TAFB and SAB.

The tropical depression appears to have continued its eastward
track this morning. For the next day or so, a continued eastward
track is likely. After that, the uncertainty is quite large. Over
the weekend, Gert will likely begin to gain latitude as its steering
is influenced by the much larger Idalia to its northwest, and a
ridge to its east. However, the models have pretty large differences
in how fast Gert may move once it begins to turn. Regardless of its
exact track, by day 4, Gert should either become a poorly defined
post-tropical cyclone or be absorbed into the circulation of Idalia.
The NHC forecast is slower and farther south than the previous
advisory to remain near the multi-model consensus.

The shear currently affecting Gert will likely remain in place for
the next few days, which covers about the entirety that Gert is
expected to last as a tropical cyclone. Nonetheless, Gert is
already very near the threshold to become a tropical storm again,
and it would not take much increase in convection or organization
for that to happen. Later in the forecast period, Gert is forecast
to weaken and dissipate. Though there is a chance it could become
post-tropical without being absorbed into Idalia, if that happens
its low-level center will likely become poorly defined in the
process, still resulting in dissipation for the purposes of this
forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 28.7N 54.6W 30 KT 35 MPH
12H 02/0000Z 28.8N 53.6W 35 KT 40 MPH
24H 02/1200Z 28.9N 52.9W 35 KT 40 MPH
36H 03/0000Z 29.7N 52.2W 35 KT 40 MPH
48H 03/1200Z 30.5N 51.6W 30 KT 35 MPH
60H 04/0000Z 32.7N 51.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
72H 04/1200Z 35.4N 51.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 05/1200Z...DISSIPATED

$$
Forecaster D. Zelinsky

[cycloneye]

Tropical Storm Gert Discussion Number 16
NWS National Hurricane Center Miami FL AL062023
500 PM AST Fri Sep 01 2023

Gert appears to have strengthened and has become a tropical storm
once again. Satellite intensity estimates range from 30 kt (1800 UTC
SAB Dvorak Current Intensity) to 46 kt (1701 UTC UW-CIMSS SATCON),
so the intensity has been raised to 35 kt in this advisory. AMSR
microwave imagery from a few hours ago revealed Gert has a tight
well-defined low-level inner-core, and it's possible the 35-kt
estimate is conservative.

The AMSR pass was also the first clear indication that Gert is
centered a little farther south than previously estimated. It's
possible that Gert's deep convection, which is limited to the
southeast quadrant, is pulling the center slowly in that direction
in the absence of other strong steering currents right now. In a
couple days, Gert should move a little quicker toward the northeast,
steered by a combination of Idalia to its northwest and a low- to
mid-level ridge over the eastern and central Atlantic. The NHC track
forecast is very close to the multi-model consensus aids TVCN and
HCCA, but is a little slower than the previous advisory.

Although continued shear should prevent Gert from strengthening
much, additional slight intensification is possible today or
tomorrow. Most models show the cyclone becoming post-tropical in 48
to 60 hours, and absorbed into the much larger circulation of Idalia
soon after. The NHC intensity forecast has been adjusted slightly
higher but is still very similar to the previous advisory. One thing
to note, the model trackers used to help NHC make track and
intensity forecasts appear to be following Idalia at the end of the
forecast instead of Gert in many cases. Users should be aware that
the tracks and intensities in the NCEP tracker or ATCF files may not
be representative of the model depiction of Gert beyond 60-72 h.


FORECAST POSITIONS AND MAX WINDS

INIT 01/2100Z 27.8N 54.4W 35 KT 40 MPH
12H 02/0600Z 27.7N 53.9W 40 KT 45 MPH
24H 02/1800Z 28.4N 53.2W 40 KT 45 MPH
36H 03/0600Z 29.0N 52.7W 35 KT 40 MPH
48H 03/1800Z 30.6N 51.9W 35 KT 40 MPH
60H 04/0600Z 33.0N 51.2W 35 KT 40 MPH...POST-TROP/EXTRATROP
72H 04/1800Z...DISSIPATED

$$
Forecaster D. Zelinsky

[cycloneye]

Tropical Storm Gert Discussion Number 17
NWS National Hurricane Center Miami FL AL062023
1100 PM AST Fri Sep 01 2023

Gert remains relatively stationary to the southeast of Idalia. The
tropical storm is quite compact and deep convection has been
persisting, mostly to the south of the center. The Dvorak
classifications from TAFB and SAB are steady at 2.5/35 kt. but the
other satellite estimates from CIMSS at the University of Wisconsin
are a little higher. Blending all of the satellite estimates
supports increasing the intensity to 40 kt.

Gert has barely moved during the past 12 hours as it is caught in
weak steering currents between Idalia and a mid- to upper-level low
over the central Atlantic. As Idalia moves closer to Gert, the
storm is expected to turn northward on Saturday, and that motion
should continue until it dissipates by early Monday.

The storm has been resilient in an environment of strong northerly
shear. Although the shear is expected to remain high, it seems
likely that Gert will maintain its strength or weaken only slightly
until it becomes absorbed by Idalia in a couple of days.


FORECAST POSITIONS AND MAX WINDS

INIT 02/0300Z 28.2N 54.9W 40 KT 45 MPH
12H 02/1200Z 28.3N 54.4W 40 KT 45 MPH
24H 03/0000Z 29.1N 53.8W 40 KT 45 MPH
36H 03/1200Z 30.3N 53.1W 35 KT 40 MPH
48H 04/0000Z 32.0N 52.4W 35 KT 40 MPH
60H 04/1200Z...DISSIPATED

$$
Forecaster Cangialosi

[cycloneye]

Tropical Storm Gert Discussion Number 18
NWS National Hurricane Center Miami FL AL062023
500 AM AST Sat Sep 02 2023

This morning's conventional satellite imagery and a recent AMSR2
microwave overpass indicate some improvement in the cloud pattern
overnight, although Gert's surface center remains near the
northern edge of the convective canopy where the colder cloud top
temperatures are evident. The subjective and objective satellite
intensity estimates have increased a bit during the past 6 hours,
and the initial intensity is bumped up to 40 kt for this advisory.

Gert's intensity shouldn't change much during the next few days
while the cyclone continues moving in a harsh northerly wind shear
environment. Gert is forecast to become a post-tropical cyclone
during the next couple of days as indicated in the global
models fields and their simulated infrared imagery forecasts.
Afterwards, Gert is expected to become absorbed by Post-Tropical
Idalia. The official intensity forecast follows the IVCN intensity
consensus aid through the period and indicates dissipation in 60
hours.

Gert should commence a northward track later today while the
southerly peripheral steering flow of larger Idalia captures the
cyclone and a subtropical ridge builds westward over the central
tropical Atlantic. There is quite a bit of along-track spread of
the models, however, so the best solution for the NHC forecast
track is to side with the consensus models, HCCA and TVCA through
dissipation early this week.


FORECAST POSITIONS AND MAX WINDS

INIT 02/0900Z 27.7N 54.3W 40 KT 45 MPH
12H 02/1800Z 28.0N 53.8W 40 KT 45 MPH
24H 03/0600Z 29.2N 53.1W 40 KT 45 MPH
36H 03/1800Z 30.8N 52.3W 35 KT 40 MPH
48H 04/0600Z 33.4N 51.7W 35 KT 40 MPH...POST-TROPICAL
60H 04/1800Z...DISSIPATED

$$
Forecaster Roberts

[cycloneye]

Tropical Storm Gert Discussion Number 19
NWS National Hurricane Center Miami FL AL062023
1100 AM AST Sat Sep 02 2023

Gert is one tough little cyclone. Satellite images indicate that
deep convection continues near the center of the storm, despite
northerly shear, and microwave data from this morning shows healthy
banding structure. A scatterometer pass from 1259 UTC shows peak
winds of just over 40 kt, which supports at least 45 kt due to the
small size of Gert. The initial wind speed is raised to 45 kt,
which also matches the latest TAFB Dvorak value and the UW-CIMSS
SATCON estimate.

The storm is moving a bit faster to the north-northeast this
morning, roughly 3 kt, as it begins to feel the steering from
Idalia to the west-northwest. Gert should accelerate north-
northeastward later today and turn northward tomorrow around the
eastern side of Idalia's large circulation. All of the global
models open Gert up into a trough of low pressure by 48 h due to
rapidly increasing forward motion around Idalia, and the official
forecast follows suit. Little change in strength is expected with
Gert before it dissipates, although this system has been more
resilient to shear than most small tropical cyclones. No
significant changes were made to the previous NHC track forecast,
with a small upward adjustment to the intensity forecast based on
the initial value.


FORECAST POSITIONS AND MAX WINDS

INIT 02/1500Z 27.8N 54.1W 45 KT 50 MPH
12H 03/0000Z 28.5N 53.6W 45 KT 50 MPH
24H 03/1200Z 30.1N 52.8W 40 KT 45 MPH
36H 04/0000Z 32.6N 51.8W 40 KT 45 MPH
48H 04/1200Z...DISSIPATED

$$
Forecaster Blake

[cycloneye]

Tropical Storm Gert Discussion Number 20
NWS National Hurricane Center Miami FL AL062023
500 PM AST Sat Sep 02 2023

Satellite images indicate that Gert has become less organized since
this morning. The low-level center is now exposed, with decreasing
deep convection. Intensity estimates support keeping Gert at 45 kt
for now, which remains near the UW-CIMSS SATCON value.

The storm is finally moving at a more substantial pace, north-
northeast at 8 kt, as it gets caught up in flow around Idalia to
the west-northwest. Gert should continue to accelerate north-
northeastward tonight and northward tomorrow around the eastern
side of Idalia's large circulation. The global models remain
consistent in showing the small circulation of Gert getting
torn apart by Idalia on Monday, reminiscent of the way that
Franklin took care of Jose yesterday. No substantial changes in
intensity are expected as any decrease in organization should be
roughly compensated by the large increase in forward. The new NHC
track and intensity forecast are basically unchanged from the
previous ones.


FORECAST POSITIONS AND MAX WINDS

INIT 02/2100Z 28.4N 53.8W 45 KT 50 MPH
12H 03/0600Z 29.8N 53.0W 40 KT 45 MPH
24H 03/1800Z 32.1N 52.0W 40 KT 45 MPH
36H 04/0600Z 35.5N 51.5W 40 KT 45 MPH
48H 04/1800Z...DISSIPATED

$$
Forecaster Blake

[cycloneye]

Tropical Storm Gert Discussion Number 21
NWS National Hurricane Center Miami FL AL062023
1100 PM AST Sat Sep 02 2023

Gert remains a resilient compact tropical storm in strong wind
shear conditions and has even managed to strengthen a little more.
The low-level center is partially exposed on the northeast side of
the main area of deep convection. An ASCAT pass from around 00Z
showed peak winds in the 45-50 kt range in the southeast quadrant,
and based on that data, the initial wind speed is increased to 50
kt. This value is above the latest satellite intensity estimates.

The tropical storm is moving north-northeastward at 5 kt. This
motion with a gradual increase in forward speed is expected during
the next day or so as the system gets swept up by the much larger
circulation of Post-Tropical Cyclone Idalia. Most of the models
show Gert dissipating in a day or so, and the NHC forecast has now
moved up dissipation to 36 hours based on that guidance.


FORECAST POSITIONS AND MAX WINDS

INIT 03/0300Z 29.1N 53.4W 50 KT 60 MPH
12H 03/1200Z 30.7N 52.6W 50 KT 60 MPH
24H 04/0000Z 33.6N 51.9W 45 KT 50 MPH
36H 04/1200Z...DISSIPATED

$$
Forecaster Cangialosi

[cycloneye]

Tropical Storm Gert Discussion Number 22
NWS National Hurricane Center Miami FL AL062023
500 AM AST Sun Sep 03 2023

Gert appears to be maintaining its intensity for the time being, in
spite of the presence of strong northeasterly vertical wind shear.
The system has been producing a blob of deep convection to the
southwest of the estimated center and the low-level circulation is
still fairly well defined on GOES-16 proxy-vis imagery. The
current intensity is kept at 50 kt for this advisory in agreement
with an Advanced Dvorak Technique estimate from UW-CIMSS.

The tropical storm is accelerating north-northeastward at a faster
forward speed of around 10 kt. A north-northeastward to
northward motion with a continued increase in forward speed is
likely during the next day or so as Gert becomes entrained into the
eastern portion of the much larger circulation of Post-Tropical
Cyclone Idalia. Global model guidance shows the system becoming
absorbed by Idalia and dissipating in 24 hours or so. The official
forecast is similar to that from the previous advisory.


FORECAST POSITIONS AND MAX WINDS

INIT 03/0900Z 29.9N 52.9W 50 KT 60 MPH
12H 03/1800Z 32.2N 52.0W 50 KT 60 MPH
24H 04/0600Z 36.3N 52.0W 45 KT 50 MPH
36H 04/1800Z...DISSIPATED

$$
Forecaster Pasch

[cycloneye]

Tropical Storm Gert Discussion Number 23
NWS National Hurricane Center Miami FL AL062023
1100 AM AST Sun Sep 03 2023

Gert may finally be on the verge of weakening. Its low-level center
has become exposed to the northeast of a shrinking area of
convection. That said, Dvorak-based satellite intensity estimates
have not started to decrease quite yet, so the intensity estimate
remains 50 kt for this advisory. A drifting buoy just south of
Gert's center reported a minimum pressure of 999 mb at 1200 UTC,
which also supports a minimum pressure similar to previous NHC
estimates. Partial ASCAT or SAR data may be available later today to
provide additional information on Gert's wind field.

Gert is accelerating north-northeastward. Additional acceleration is
expected as Gert begins its anticipated rotation around the much
larger circulation of Post-Tropical Cyclone Idalia, located to the
northwest of Gert. As Gert quickly rotates northward around the
eastern side of Idalia, all available dynamical guidance indicates
Gert will weaken slightly and open into a trough. The NHC forecast
maintains Gert as a tropical cyclone a little longer than the models
since most of them seem to be having trouble initializing the small
tropical storm appropriately. The NHC track, intensity, and wind
radii forecasts are all very similar to the previous advisory.


FORECAST POSITIONS AND MAX WINDS

INIT 03/1500Z 31.2N 51.9W 50 KT 60 MPH
12H 04/0000Z 34.1N 51.6W 45 KT 50 MPH
24H 04/1200Z 38.8N 52.8W 45 KT 50 MPH
36H 05/0000Z...DISSIPATED

$$
Forecaster D. Zelinsky

[cycloneye]

Tropical Storm Gert Discussion Number 24
NWS National Hurricane Center Miami FL AL062023
500 PM AST Sun Sep 03 2023

All indications suggest that Gert is finally weakening. Gert's
center has been intermittently exposed since sunrise, displaced to
the northeast from a small area of persistent deep convection.
Dvorak estimates from TAFB, SAB, and the UW-CIMSS ADT have all
decreased from earlier values. The initial intensity of 45 kt is a
little above a consensus of the various satellite estimates, but I
would rather only make a small change until we get a surface wind
retrieval or another data set to help confirm the apparent weakening
trend.

Gert continues to accelerate toward the north-northeast. A turn
northward as Gert continues to speed up and wrap around the eastern
periphery of Post-Tropical Cyclone Idalia should begin soon. Most
models indicate that Gert will dissipate in the next 12 h or so, but
the NHC forecast carries it through 24 h since Gert has repeatedly
lasted longer than any model forecast indicated it should. The NHC
track and intensity forecasts are again very similar to previous
advisories, near the HCCA and simple consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT 03/2100Z 32.8N 51.3W 45 KT 50 MPH
12H 04/0600Z 36.1N 51.3W 40 KT 45 MPH
24H 04/1800Z 40.0N 54.6W 40 KT 45 MPH
36H 05/0600Z...DISSIPATED

$$
Forecaster D. Zelinsky

[cycloneye]

Tropical Storm Gert Discussion Number 25
NWS National Hurricane Center Miami FL AL062023
1100 PM AST Sun Sep 03 2023

The low-level center of Gert is exposed in proxy-visible satellite
images tonight. Recent ASCAT-B wind retrievals indicate the surface
center is becoming elongated and less defined. There are still
tropical-storm-force winds occurring in the eastern semicircle, with
scatterometer winds as high as 40-42 kt. However, this is more a
product of Gert's translational speed than its paltry convective
structure. Based on these data, the initial intensity is held at 45
kt for this advisory.

Gert is moving quickly northward (010/19 kt) while being captured
within the broader cyclonic flow associated with Post-Tropical
Cyclone Idalia. Gert is forecast to accelerate northward to
north-northwestward while it continues rounding the northeastern
portion of Idalia's circulation. The global models show Gert
becoming absorbed on Monday, and the updated NHC forecast predicts
dissipation by 24 h. However, it is entirely possible that Gert
opens into a trough even sooner based on its current structure.


FORECAST POSITIONS AND MAX WINDS

INIT 04/0300Z 35.4N 50.7W 45 KT 50 MPH
12H 04/1200Z 38.5N 52.3W 40 KT 45 MPH
24H 05/0000Z...DISSIPATED

$$
Forecaster Reinhart

[cycloneye]

Tropical Storm Gert Discussion Number 26
NWS National Hurricane Center Miami FL AL062023
500 AM AST Mon Sep 04 2023

A small area of disorganized deep convection has been persisting to
the southeast of the estimated center position. The intensity
estimate of 45 kt is based on continuity from earlier scatterometer
data and a Dvorak CI-number from TAFB. However, the low-level
circulation of Gert is becoming increasingly disrupted by the much
larger post-tropical cyclone Idalia. In fact, Gert may no longer
have a closed circulation, and it is likely that the system will
become absorbed by Idalia, and dissipate, later today.

Gert is moving northward at a faster forward speed of around 21 kt.
The cyclone should gradually turn northwestward with additional
acceleration while it rotates around Idalia, before dissipating.
The official track forecast is similar to the previous one.


FORECAST POSITIONS AND MAX WINDS

INIT 04/0900Z 37.6N 51.0W 45 KT 50 MPH
12H 04/1800Z 40.6N 53.8W 40 KT 45 MPH
24H 05/0600Z...DISSIPATED

$$
Forecaster Pasch

[cycloneye]

Remnants Of Gert Discussion Number 27
NWS National Hurricane Center Miami FL AL062023
1100 AM AST Mon Sep 04 2023

Visible satellite imagery indicates that Gert has dissipated. It is
also no longer producing organized deep convection. Therefore, this
is the final NHC advisory on Gert.

SAR data around 0930 UTC indicated that the remnants of Gert were
still producing winds near 45 kt, and that is the basis for the max
wind analysis. The remnants of Gert will continue to move quickly
around the circulation of Post-Tropical Cyclone Idalia today. Gert
will likely be fully absorbed by Idalia by tomorrow, so there does
not appear to be any potential for another regeneration of Gert.


FORECAST POSITIONS AND MAX WINDS

INIT 04/1500Z 40.5N 51.0W 45 KT 50 MPH...REMNANTS OF GERT
12H 05/0000Z...DISSIPATED

$$
Forecaster D. Zelinsky