ATL: JOYCE - Advisories

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cycloneye
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ATL: JOYCE - Advisories

#1 Postby cycloneye » Wed Sep 12, 2018 3:41 pm

BULLETIN
Subtropical Storm Joyce Advisory Number 1
NWS National Hurricane Center Miami FL AL102018
500 PM AST Wed Sep 12 2018

...JOYCE FORMS IN THE NORTH ATLANTIC...

SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...34.3N 41.9W
ABOUT 870 MI...1395 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...SW OR 220 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 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 newly formed Subtropical
Storm Joyce was located near latitude 34.3 North, longitude 41.9
West. The storm is moving toward the southwest near 6 mph (9 km/h),
and this slow motion should continue during the next couple of days.

Maximum sustained winds are near 45 mph (75 km/h) with higher gusts.
Joyce is forecast to transform into a tropical storm by Thursday
and strengthen some.

Winds of 40 mph extend outward up to 115 miles (185 km) from the
center.

The estimated minimum central pressure is 1006 mb (29.71 inches).


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


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

$$
Forecaster Avila

Subtropical Storm Joyce Discussion Number 1
NWS National Hurricane Center Miami FL AL102018
500 PM AST Wed Sep 12 2018

The strong low pressure system which the NHC has been monitoring in
the north Atlantic for a couple of days has developed a cyclonically
curved band of deep convection near the center, and scatterometer
data indicate that the winds are near 40 kt. Since the system is
still vertically stacked with an upper-low, it is then classified
as a subtropical cyclone at this time. However, the cyclone is
gaining organization while it is acquiring tropical characteristics.
The NHC forecast calls for Joyce to transform into a tropical system
in about 12 to 24 hours. Since the ocean is warm, some slight
strengthening is possible during the next 3 days. After that time,
Joyce will be over cooler waters and should then be absorbed by a
larger extratropical low.

Joyce has been moving southwestward or 225 degrees at 5 kt, steered
by the northerly flow around the subtropical high which has been
steering Florence and to west of the mid-latitude trough which
is forcing Helene to recurve. In a couple of days, global models
indicate that the steering pattern will change as the trough
amplifies, and Joyce should then turn toward the northeast with an
increase in forward speed.


FORECAST POSITIONS AND MAX WINDS

INIT 12/2100Z 34.3N 41.9W 40 KT 45 MPH
12H 13/0600Z 33.7N 42.6W 40 KT 45 MPH...TROPICAL STORM
24H 13/1800Z 33.0N 43.5W 40 KT 45 MPH
36H 14/0600Z 32.5N 43.5W 45 KT 50 MPH
48H 14/1800Z 32.5N 43.5W 50 KT 60 MPH
72H 15/1800Z 34.0N 41.0W 50 KT 60 MPH
96H 16/1800Z 37.0N 35.0W 40 KT 45 MPH
120H 17/1800Z...ABSORBED

$$
Forecaster Avila
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Re: ATL: JOYCE - Advisories

#2 Postby cycloneye » Wed Sep 12, 2018 9:50 pm

BULLETIN
Subtropical Storm Joyce Advisory Number 2
NWS National Hurricane Center Miami FL AL102018
1100 PM AST Wed Sep 12 2018

...SUBTROPICAL STORM JOYCE MOVING SLOWLY SOUTHWESTWARD OVER THE
NORTHEAST ATLANTIC...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...34.1N 42.6W
ABOUT 910 MI...1465 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...SW OR 220 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES



Subtropical Storm Joyce Discussion Number 2
NWS National Hurricane Center Miami FL AL102018
1100 PM AST Wed Sep 12 2018

Joyce still has subtropical characteristics. Although a small area
of convection has recent developed near the storm's center, cloud
tops are not particularly cold and the cyclone is still co-located
with an upper-level low. The initial intensity has been held at 40
kt based on a subtropical intensity estimate of 35-40 kt from
TAFB. This could be generous estimate since a recent near-miss of
the ASCAT instrument to the west of Joyce suggested that the winds
may have decreased somewhat since earlier today.

Little change has been made to the track or intensity forecast.
Just about all of the intensity guidance continues to indicate that
some gradual strengthening is possible during the next day or two
while Joyce continues to acquire tropical characteristics. By 72 h,
the global and statistical models depict Joyce weakening due to a
drastic increase in shear and a decrease in environmental humidity
until it is absorbed into a larger mid-latitude trough around 96 h.
The HWRF and HMON models show a very different solution where Joyce
strengthens to hurricane strength despite the marginal environment.
This scenario seems less likely at this time, so the NHC intensity
forecast is just below the intensity consensus beyond 36 h.

Joyce is caught in fairly light steering currents between strong
ridges to its east and west, and the initial motion estimate is
220/5 kt. All of the global models forecast only a slow
southwestward motion during the next couple of days, particularly
as Hurricane Helene approaches from the southeast. Once Helene
passes to the east, Joyce will likely quickly turn northeastward and
accelerate ahead of the aforementioned mid-latitude trough before
dissipating southwest of the Azores. The official track forecast is
basically a blend of the previous advisory and the corrected
consensus aids HCCA and FSSE.


FORECAST POSITIONS AND MAX WINDS

INIT 13/0300Z 34.1N 42.6W 40 KT 45 MPH
12H 13/1200Z 33.5N 43.3W 40 KT 45 MPH
24H 14/0000Z 32.9N 43.8W 45 KT 50 MPH...TROPICAL STORM
36H 14/1200Z 32.5N 44.0W 50 KT 60 MPH
48H 15/0000Z 32.3N 43.4W 50 KT 60 MPH
72H 16/0000Z 34.2N 40.0W 45 KT 50 MPH
96H 17/0000Z 37.0N 33.5W 40 KT 45 MPH
120H 18/0000Z...DISSIPATED

$$
Forecaster Zelinsky
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Re: ATL: JOYCE - Advisories

#3 Postby southerngale » Thu Sep 13, 2018 4:03 am

439
WTNT35 KNHC 130856
TCPAT5

BULLETIN
Subtropical Storm Joyce Advisory Number 3
NWS National Hurricane Center Miami FL AL102018
500 AM AST Thu Sep 13 2018

...JOYCE DRIFTING SOUTHWESTWARD WITH NO CHANGE IN STRENGTH...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...33.8N 43.1W
ABOUT 945 MI...1520 KM WSW OF THE AZORES
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...SW OR 220 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 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 Subtropical Storm Joyce was
located near latitude 33.8 North, longitude 43.1 West. The storm is
moving toward the southwest near 6 mph (9 km/h). A slow
southwestward motion is expected for the next couple of days. A turn
toward the northeast with a rapid increase in forward motion is
forecast to occur over the weekend.

Maximum sustained winds are near 45 mph (75 km/h) with higher gusts.
Some slight strengthening is possible during the next couple of
days. Joyce could become a tropical storm within the next day or
so.

Winds of 40 mph extend outward up to 80 miles (130 km) from the
center, mainly to the northwest.

The estimated minimum central pressure is 1006 mb (29.71 inches).


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


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

$$
Forecaster Zelinsky

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Re: ATL: JOYCE - Advisories

#4 Postby southerngale » Thu Sep 13, 2018 4:04 am

024
WTNT45 KNHC 130858
TCDAT5

Subtropical Storm Joyce Discussion Number 3
NWS National Hurricane Center Miami FL AL102018
500 AM AST Thu Sep 13 2018

Joyce is still co-located with an upper-level low, and the most
recent TAFB intensity classification was still a subtropical type.
Furthermore, there has been no discernible increase of convection
near the center of the cyclone, and cloud tops have actually warmed
over the past few hours. Therefore, Joyce is still classified as
subtropical for this advisory. Since the cyclone hasn't changed
much in organization, the initial intensity has been held at 40 kt
based on the TAFB subtropical intensity estimate, but this is still
possibly generous.

Joyce's struggle to maintain deep convection bodes poorly for its
intensification prospects, considering that the shear is forecast
by the global models to increase considerably over the next few
days. SHIPS, LGEM, and the global models continue to show Joyce
changing little in strength over the next few days until the
system dissipates by early next week. The HWRF and HMON models are
still outliers in showing substantial intensification, but even
these models aren't quite as aggressive in strengthening Joyce as
they were previously. The NHC forecast continues to favor the
statistical guidance and is just below the intensity consensus at
most forecast hours because it is frankly hard to believe that Joyce
will become a hurricane in 48 h based on its current appearance.

Joyce is still moving slowly southwestward with an initial motion
of 220/5 kt. The global models remain in fairly good agreement
that Joyce will move slowly southwestward for the next day or
so as the storm remains in light steering flow. A turn toward the
south will likely occur as Helene approaches from the southeast,
followed by a quick turn northeastward once the larger tropical
cyclone passes by. Joyce should then accelerate quickly
northeastward ahead of a mid-latitude trough before dissipating
southwest of the Azores. Little change was made to the official
track forecast which is near the middle of the various consensus
aids.


FORECAST POSITIONS AND MAX WINDS

INIT 13/0900Z 33.8N 43.1W 40 KT 45 MPH
12H 13/1800Z 33.3N 43.8W 40 KT 45 MPH
24H 14/0600Z 32.6N 44.2W 45 KT 50 MPH
36H 14/1800Z 32.0N 44.0W 45 KT 50 MPH
48H 15/0600Z 32.1N 43.2W 45 KT 50 MPH
72H 16/0600Z 34.6N 39.4W 40 KT 45 MPH
96H 17/0600Z 37.0N 32.5W 40 KT 45 MPH
120H 18/0600Z...DISSIPATED

$$
Forecaster Zelinsky

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Re: ATL: JOYCE - Advisories

#5 Postby cycloneye » Thu Sep 13, 2018 10:05 am

Subtropical Storm Joyce Discussion Number 4
NWS National Hurricane Center Miami FL AL102018
1100 AM AST Thu Sep 13 2018

Joyce's satellite presentation is less than impressive this morning,
with the low-level center exposed to the northwest of a small patch
of deep convection. The initial intensity is set to 35 kt based on
the latest subtropical classification of ST2.5 from TAFB a 1208Z
ASCAT-B overpass that showed 30-35 kt winds north and northeast of
the center. Cyclone phase space diagrams still show Joyce with a
shallow-to-moderate warm core, and the system remains a subtropical
storm for now.

Little change in intensity is expected during the next few days, as
Joyce will continue to be affected by strong westerly-to-
southwesterly vertical wind shear. The new NHC forecast is a little
below the intensity consensus given the weakening trend seen in the
global models. Dissipation is shown at 96 hours, but it wouldn't be
surprising if Joyce becomes a post-tropical cyclone before that.

The initial motion estimate is 245/05. Joyce is currently situated
a little to the west of an upper-level low, which is currently
steering the system southwestward and southward, and that should
continue for the next day or so. Then, Joyce should begin to
accelerate northeastward ahead of an approaching mid-level trough.
The new NHC track forecast follows the trend of the latest
guidance, and is a little to the west of the previous one through
36 hours. The official forecast is close to the latest HCCA and
TVCA consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT 13/1500Z 33.7N 43.7W 35 KT 40 MPH
12H 14/0000Z 33.1N 44.1W 35 KT 40 MPH
24H 14/1200Z 32.2N 44.4W 40 KT 45 MPH
36H 15/0000Z 31.9N 44.0W 40 KT 45 MPH
48H 15/1200Z 32.5N 42.6W 40 KT 45 MPH
72H 16/1200Z 35.5N 38.5W 35 KT 40 MPH
96H 17/1200Z...DISSIPATED

$$
Forecaster Brennan
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Re: ATL: JOYCE - Advisories

#6 Postby cycloneye » Thu Sep 13, 2018 9:58 pm

Tropical Storm Joyce Discussion Number 6
NWS National Hurricane Center Miami FL AL102018
1100 PM AST Thu Sep 13 2018

Beginning around 6 hours ago, convection redeveloped near the center
of Joyce. Since then, the cyclone has become displaced from the
upper-level low, and an ASCAT overpass around 2330 UTC showed that
Joyce has a small radius of maximum winds of around 30 n mi. Based
on these factors, it appears Joyce has become a tropical cyclone.
The ASCAT pass showed maximum winds of just over 30 kt, but its
possible the instrument slightly under-sampled the maximum winds of
the small cyclone. In addition, convection near the center
increased somewhat after the time of the ASCAT pass. The initial
intensity has therefore been held at 35 kt, making Joyce a tropical
storm.

Joyce has accelerated a little toward the west-southwest, perhaps
more than previously anticipated. As a result, the forecast has
been shifted south at most forecast hours, but not quite as far as
the consensus models would suggest. There is otherwise no change
to the track forecast reasoning, and Joyce is still expected to move
slowly generally southward while Helene passes to the east until
accelerating toward the northeast ahead of a mid-latitude trough in
a day or two.

Despite the recent, and perhaps temporary, resurgence of
convection, no change has been made to the intensity forecast.
None of the guidance shows much intensification, and the NHC
forecast continues to rely on a blend of the intensity consensus
and the GFS and ECMWF, which only show gradual weakening throughout
the forecast period. Considering that the cyclone has only
gradually weakened to this point, this still seems like a reasonable
forecast.

FORECAST POSITIONS AND MAX WINDS

INIT 14/0300Z 32.9N 44.4W 35 KT 40 MPH
12H 14/1200Z 32.2N 44.7W 35 KT 40 MPH
24H 15/0000Z 31.7N 44.2W 35 KT 40 MPH
36H 15/1200Z 32.2N 43.3W 35 KT 40 MPH
48H 16/0000Z 33.3N 42.1W 30 KT 35 MPH
72H 17/0000Z 36.0N 37.5W 30 KT 35 MPH
96H 18/0000Z...DISSIPATED

$$
Forecaster Zelinsky
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Re: ATL: JOYCE - Advisories

#7 Postby cycloneye » Sat Sep 15, 2018 3:38 pm

Tropical Storm Joyce Discussion Number 13
NWS National Hurricane Center Miami FL AL102018
500 PM AST Sat Sep 15 2018

The circulation of Joyce is elongated this afternoon, with the
center partially exposed. It has been interesting to watch deep
convection firing in the northeastern quadrant, kicking off new
small swirls that rotate around the mean circulation. A blend of
the Dvorak estimates from TAFB/SAB supports keeping the wind speed
40 kt on this advisory.

There is no change to the intensity forecast reasoning. The
environment is predicted to be nearly steady-state around Joyce
through Sunday, with strong shear being offset by waters near 27C.
Thereafter, as the hostile shear continues, the mid-level air should
become drier near the center, and SSTs cool off below 26C. These
conditions should cause Joyce to slowly weaken early next week, and
dissipate in 3 days or so. This forecast is basically the same as
the previous one, but it isn't out of the realm of possibility the
cyclone could open up into a trough before that time.

Joyce continues to accelerate, now moving east-northeastward at
about 15 kt. The storm remains embedded within the same trough as
Tropical Storm Helene, and Joyce should move east-northeastward
during the next day or so. Beyond that time, as Joyce becomes a
shallow cyclone, it is forecast to turn southeastward due to
low-level flow around the eastern side of a building ridge over the
central Atlantic Ocean. The track forecast is simply an update to
the previous one, and continues to be on the southern side of the
guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 15/2100Z 33.1N 39.6W 40 KT 45 MPH
12H 16/0600Z 34.1N 37.2W 40 KT 45 MPH
24H 16/1800Z 34.8N 33.8W 40 KT 45 MPH
36H 17/0600Z 34.8N 30.5W 35 KT 40 MPH
48H 17/1800Z 34.0N 28.0W 30 KT 35 MPH
72H 18/1800Z 31.5N 26.5W 25 KT 30 MPH
96H 19/1800Z...DISSIPATED

$$
Forecaster Blake
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Re: ATL: JOYCE - Advisories

#8 Postby cycloneye » Sun Sep 16, 2018 9:42 am

Tropical Depression Joyce Discussion Number 16
NWS National Hurricane Center Miami FL AL102018
1100 AM AST Sun Sep 16 2018

Joyce is barely a tropical cyclone at the moment. The cloud
pattern consists of a low-level swirl with a small patch of deep
convection located about 80 n mi northeast of the center and another
patch of weakening convection well removed from the center in the
northeast quadrant. Visible satellite images and a partial ASCAT
pass indicate that the circulation of the cyclone has also become
increasingly elongated from northeast to southwest. Based on the
system's appearance and the satellite intensity estimates, the
initial wind speed is lowered to 30 kt, making Joyce a tropical
depression.

The depression is moving east-northeastward at 16 kt within the
mid-latitude westerlies, and this motion should continue through
tonight. After that time, the shallow cyclone is expected to slow
down and turn southeastward and then southwestward as it is moves
in the flow on the east side of a building low- to mid-level ridge.
The track models are in fairly good agreement, and little overall
change was made to the previous NHC forecast.

Joyce is currently in a quite hostile environment of 30-40 kt of
west-southwesterly shear. Even though SSTs are relatively warm,
the ongoing strong shear and nearby dry air should continue to cause
the cyclone to gradually weaken. Although the NHC forecast shows
Joyce hanging on as a tropical depression for a couple of more days,
it is very possible that the system could degenerate into a trough
or a remnant low at any time during that period.

FORECAST POSITIONS AND MAX WINDS

INIT 16/1500Z 34.7N 34.3W 30 KT 35 MPH
12H 17/0000Z 34.9N 31.4W 30 KT 35 MPH
24H 17/1200Z 34.5N 28.7W 30 KT 35 MPH
36H 18/0000Z 33.6N 27.0W 30 KT 35 MPH
48H 18/1200Z 32.6N 26.7W 25 KT 30 MPH
72H 19/1200Z 30.4N 29.2W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 20/1200Z...DISSIPATED

$$
Forecaster Cangialosi
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Re: ATL: JOYCE - Advisories

#9 Postby cycloneye » Sun Sep 16, 2018 3:42 pm

Tropical Depression Joyce Discussion Number 17
NWS National Hurricane Center Miami FL AL102018
500 PM AST Sun Sep 16 2018

Joyce continues to hang on as a tropical depression. The cloud
pattern consists of a swirl of low-level clouds with patches
of deep convection that become sheared off in the northeast
quadrant. The initial intensity is held at 30 kt, in agreement
with an ASCAT pass from several hours ago that showed maximum winds
in the 25-30 kt range. Even though Joyce is over relatively warm
water, the current hostile atmospheric environment of 30-40 kt of
west-southwesterly shear and nearby dry air should cause Joyce to
gradually weaken during the next few days. Although remnant low
status is not predicted to occur for 2-3 days, it is very possible
that Joyce could degenerate into a trough or a remnant low well
before then.

The depression has turned to the east, with the latest initial
motion estimate being 090/15. The weak and shallow system is
expected to move in the low- to mid-level flow during the next few
days. This should cause the cyclone to slow down and turn
southeastward on Monday, followed by a southward and then
southwestward motion on Tuesday and Wednesday as the system moves
around a building ridge over the northeastern Atlantic. The track
models are in fairly good agreement, and only small changes were
made to the previous NHC forecast.

FORECAST POSITIONS AND MAX WINDS

INIT 16/2100Z 34.4N 32.6W 30 KT 35 MPH
12H 17/0600Z 34.2N 30.2W 30 KT 35 MPH
24H 17/1800Z 33.6N 28.0W 30 KT 35 MPH
36H 18/0600Z 32.4N 27.0W 25 KT 30 MPH
48H 18/1800Z 31.2N 27.4W 25 KT 30 MPH
72H 19/1800Z 29.4N 30.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 20/1800Z...DISSIPATED

$$
Forecaster Cangialosi
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Re: ATL: JOYCE - Advisories

#10 Postby cycloneye » Sun Sep 16, 2018 9:51 pm

Tropical Depression Joyce Discussion Number 18
NWS National Hurricane Center Miami FL AL102018
1100 PM AST Sun Sep 16 2018

Joyce is managing to maintain tropical cyclone status despite very
strong westerly vertical wind shear. The system still displays cold
cloud tops, but only within the northeast quadrant and at least
100 nm from the center. The shear is being induced primarily by
50-kt 200 mb winds. Usually such strong vertical shear would
completely decapitate a tropical cyclone. However, systems in
higher latitudes and moving in the same direction as the shear
vector tend to be somewhat more resilient to the detrimental
effects of the shear. Nonetheless, it is anticipated that Joyce
will soon succumb to the combination of high shear, cool waters,
and dry mid-levels, and become a remnant low within 48 hours, if not
sooner. The official intensity forecast shows a gradual weakening,
nearly the same as the previous advisory and based upon a blend of
the LGEM statistical scheme and the HWRF/HMON dynamical models.

Joyce is moving toward the east at a quick 18-kt clip. The system
has not been picked up by the mid-latitude westerlies and is
expected to be advected around the lower tropospheric Bermuda-Azores
high. Joyce should slow its forward speed and turn toward the
southeast (on Monday), the south (on Tuesday), and finally the
southwest (on Wednesday) before dissipating in about four days. The
track forecast is based upon the tightly clustered TVCN multi-model
consensus and is slightly farther east because of the quicker
eastward initial motion than previously observed.

FORECAST POSITIONS AND MAX WINDS

INIT 17/0300Z 34.0N 30.3W 30 KT 35 MPH
12H 17/1200Z 33.7N 27.9W 30 KT 35 MPH
24H 18/0000Z 32.8N 26.5W 30 KT 35 MPH
36H 18/1200Z 31.7N 26.3W 25 KT 30 MPH
48H 19/0000Z 30.5N 27.1W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 20/0000Z 28.9N 29.8W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 21/0000Z...DISSIPATED

$$
Forecaster Landsea
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Re: ATL: JOYCE - Advisories

#11 Postby cycloneye » Mon Sep 17, 2018 9:45 am

Tropical Depression Joyce Discussion Number 20
NWS National Hurricane Center Miami FL AL102018
1100 AM AST Mon Sep 17 2018

Joyce is gradually losing organization, with drier air entraining
into the circulation. Visible satellite imagery this morning
shows a few cloud swirls pivoting around a mean center with
only a small amount of deep convection displaced about 90 miles
northeast of the mean center. ASCAT scatterometer data indicate
that winds of 25 to 30 kt remain on the southwestern side of the
cyclone. Based on these data, Joyce remains a 30-kt tropical
depression for this advisory. Dry air and strong vertical wind shear
are expected to continue to weaken Joyce over the next few days, and
the cyclone is expected to degenerate into a remnant low by 24
hours. The official intensity forecast is similar to the previous
advisory and remains close to the model consensus. The only notable
change is that Joyce is now expected to become a remnant low a
little faster than the previous advisory.

The initial motion is 105/07 kt. Joyce has slowed down this
morning as anticipated as it is now reaching the northeastern
periphery of a mid-level high pressure area. Over the next couple of
days, the cyclone is expected to turn southeastward, southward, and
then southwestward around the eastern periphery of the high. The
lastest track guidance is tightly clustered, with the NHC track
forecast lying in the middle of the guidance envelope, and close to
the previous official forecast track.

FORECAST POSITIONS AND MAX WINDS

INIT 17/1500Z 34.0N 28.4W 30 KT 35 MPH
12H 18/0000Z 33.5N 27.2W 30 KT 35 MPH
24H 18/1200Z 32.3N 26.6W 30 KT 35 MPH...POST-TROP/REMNT LOW
36H 19/0000Z 31.2N 27.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 19/1200Z 30.3N 28.3W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 20/1200Z 28.9N 31.3W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 21/1200Z...DISSIPATED

$$
Forecaster Cangialosi/Latto
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Re: ATL: JOYCE - Advisories

#12 Postby cycloneye » Mon Sep 17, 2018 9:55 pm

Tropical Depression Joyce Discussion Number 22
NWS National Hurricane Center Miami FL AL102018
1100 PM AST Mon Sep 17 2018

Joyce remains a very resilient tropical cyclone. After an earlier
burst of deep convection just east of the low-level center that has
since dissipated, a new convective burst has developed just north of
the center with a curved convective band trying to develop in the
eastern semicircle. All of this convective activity has been
occurring despite westerly 850-200-mb vertical wind shear of near
35 kt and in the presence of very dry mid-level air. The initial
intensity is being maintained a 30 kt based on earlier 28-kt ASCAT
wind data, and the fact that no significant change has occurred to
Joyce's low-level appearance in satellite imagery.

The initial motion estimate is now 155/06 kt. Joyce is forecast to
move around the eastern periphery of a deep-layer ridge located
across the eastern Atlantic to the southwest and west of the
cyclone. This large-scale steering feature is expected to gradually
turn Joyce toward the south overnight and on Tuesday, and then force
the cyclone toward the southwest on Wednesday and Thursday. The new
NHC track forecast is to the west of the previous advisory track,
and lies near the middle of the guidance envelope close to a blend
of the consensus models TVCA and HCCA.

Convective development during the past 12 hours has been in large
part due to the strong atmospheric instability created by very cold
200-mb temperatures near -57 deg C overlaying relatively warm ocean
temperatures of 25.5 deg C. A contributing factor to the most recent
convective development appears to be enhanced uplift caused by an
approaching shortwave trough noted in water vapor imagery between
30W-35W longitude. The latter feature is forecast by most of the
global models to cut off south of the Azores and become entangled
with Joyce's circulation over the next few days, resulting in a
sharp decrease in the vertical wind shear and an increase in
atmospheric instability/CAPE by 48 h and beyond, which would aid
convective development and re-strengthening. For now, however, the
new intensity forecast continues the weakening trend of the previous
advisories due to an abundance of very dry mid-level air being
entrained into the circulation, which is expected to shut down
convective development, causing Joyce to dissipate shortly after
72 h. However, confidence in this forecast scenario is not very
high, and some adjustments may be required to subsequent forecasts
once the 18/0000Z model guidance becomes available, especially since
the GFS- and ECMWF-based SHIPS and LGEM intensity guidance maintains
Joyce as a 30- to 35-kt tropical cyclone through the next 120 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 18/0300Z 33.2N 27.3W 30 KT 35 MPH
12H 18/1200Z 32.4N 27.1W 30 KT 35 MPH
24H 19/0000Z 31.4N 27.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 19/1200Z 30.5N 28.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 20/0000Z 29.9N 29.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 21/0000Z 29.2N 33.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 22/0000Z...DISSIPATED

$$
Forecaster Stewart
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Re: ATL: JOYCE - Advisories

#13 Postby cycloneye » Tue Sep 18, 2018 9:40 am

Tropical Depression Joyce Discussion Number 24
NWS National Hurricane Center Miami FL AL102018
Issued by the NWS Weather Prediction Center College Park MD
1100 AM AST Tue Sep 18 2018

Earlier in the morning, the low-level center of Joyce became
decoupled from a small area of deeper convection. However, another
convective burst has recently developed after 12Z closer to the
low-level center. The initial intensity of Joyce was held at 30 kt
based on a recent ASCAT pass, which showed an area of 25-30 kt winds
on the north side of the circulation. The number of wind retrievals
close to 30 kt was rather limited, so Joyce's winds should decrease
below 30 kt when it eventually loses deep convection. The
depression is in an environment with strong westerly vertical wind
shear (30-40 kt) and marginal sea surface temperatures (around 25C),
and thus the primary forecast question is when Joyce will succumb to
the relatively hostile environment, lose deep convection and become
a remnant low. The GFS and ECMWF models both show some deep
convection lingering into tomorrow before warming upper-level
temperatures and increasingly dry air aloft kill off any remaining
convection. Therefore, the 12-hour forecast point maintains tropical
depression status, and the 24-hour forecast point indicates a
post-tropical system.

The initial motion of Joyce is now more southerly (185 degrees at 7
kt), and it will begin to turn increasingly to the southwest and
west as the central Atlantic ridge builds to the north. The new
forecast track is essentially an update of the previous one, which
was close to the TVCA and HCCA consensus models. Minor adjustments
were made in the first 24 hours to account for a slightly faster
observed motion to the south in the past 6-12 hours.


FORECAST POSITIONS AND MAX WINDS

INIT 18/1500Z 31.6N 27.4W 30 KT 35 MPH
12H 19/0000Z 30.6N 27.7W 25 KT 30 MPH
24H 19/1200Z 29.9N 28.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 20/0000Z 29.4N 29.9W 20 KT 25 MPH...POST-TROP/REMNT LOW
48H 20/1200Z 29.0N 31.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 21/1200Z...DISSIPATED

$$
Forecaster Lamers/Blake
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Re: ATL: JOYCE - Advisories

#14 Postby cycloneye » Tue Sep 18, 2018 4:44 pm

Tropical Depression Joyce Discussion Number 25
NWS National Hurricane Center Miami FL AL102018
Issued by the NWS Weather Prediction Center College Park MD
500 PM AST Tue Sep 18 2018

Deep convection has generally been on the wane during the past day
or so near the center of Joyce, and it is getting very close to no
longer having organized deep convection. With the decrease in
overall organization, the initial wind speed is set to 25 kt. An
environment of strong westerly vertical wind shear (30-40 kt)
and marginal sea surface temperatures (around 25C) should cause
Joyce to become a remnant low by late tonight or early Wednesday.
This agrees well with the latest global model guidance, and the
timing of remnant low status has been moved up to 12 hours (or
less).

The initial motion of Joyce continues to turn and is now south-
southwestward (205 degrees at 6 kt). The depression is forecast
to turn increasingly to the southwest and west as the central
Atlantic ridge builds to the north. Model guidance, except the HWRF,
is tightly clustered, so the new forecast track is essentially an
update of the previous one, closest to the HCCA consensus model.


FORECAST POSITIONS AND MAX WINDS

INIT 18/2100Z 30.9N 27.8W 25 KT 30 MPH
12H 19/0600Z 30.2N 28.3W 20 KT 25 MPH...POST-TROP/REMNT LOW
24H 19/1800Z 29.6N 29.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
36H 20/0600Z 29.1N 30.9W 15 KT 15 MPH...POST-TROP/REMNT LOW
48H 20/1800Z...DISSIPATED

$$
Forecaster Campbell/Blake
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Re: ATL: JOYCE - Advisories

#15 Postby cycloneye » Tue Sep 18, 2018 9:51 pm

Post-Tropical Cyclone Joyce Discussion Number 26
NWS National Hurricane Center Miami FL AL102018
1100 PM AST Tue Sep 18 2018

During the past couple of days, Joyce had been producing patches of
deep convection that would quickly shear off due to strong westerly
winds aloft. Each convective burst appeared weaker than the
previous one, and during the past 12-18 hours, the circulation has
been nearly devoid of deep convection. Therefore, Joyce no longer
meets the criteria of a tropical cyclone, and this is the last
advisory issued by the National Hurricane Center on this system. The
initial wind speed is held at 25 kt, in agreement with a recent
ASCAT pass around 2200Z that showed maximum winds in the 20-25 kt
range. The remnant low is expected to gradually weaken and
ultimately dissipate in a couple of days due to dry and stable air,
cool SSTs, and moderate to strong westerly shear.

Joyce is moving south-southwestward at 7 kt on the east side of a
low- to mid-level ridge. A turn to the southwest is expected on
Wednesday as the ridge builds to the northeast of the cyclone, and
that motion should continue until the remnant low dissipates. The
NHC track forecast lies near the middle of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT 19/0300Z 30.4N 27.9W 25 KT 30 MPH...POST-TROP/REMNT LOW
12H 19/1200Z 29.9N 28.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
24H 20/0000Z 29.4N 29.9W 20 KT 25 MPH...POST-TROP/REMNT LOW
36H 20/1200Z 28.9N 31.5W 15 KT 15 MPH...POST-TROP/REMNT LOW
48H 21/0000Z...DISSIPATED

$$
Forecaster Cangialosi
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