ATL: PHILIPPE - Advisories

[cycloneye]

BULLETIN
Tropical Depression Seventeen Advisory Number 1
NWS National Hurricane Center Miami FL AL172023
1100 AM AST Sat Sep 23 2023

...NEW TROPICAL DEPRESSION FORMS OVER THE CENTRAL TROPICAL
ATLANTIC...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.6N 38.8W
ABOUT 985 MI...1585 KM W OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES



Tropical Depression Seventeen Discussion Number 1
NWS National Hurricane Center Miami FL AL172023
1100 AM AST Sat Sep 23 2023

Visible imagery since sunrise revealed that a small well-defined
center has formed on the western edge of an area of disturbed
weather located several hundred miles west of the Cabo Verde
Islands. Deep convection associated with the system is also
sufficiently organized to classify it as a tropical cyclone.
Therefore, advisories have been initiated on Tropical Depression
Seventeen.

ASCAT data valid around 1200 UTC indicated that maximum winds
associated with the depression are near 30 kt, and that is the basis
for the initial intensity. Since the cyclone's deep convection and
formative mid-level circulation are displaced well east of its
surface center, no significant change in strength is anticipated in
the short term. Deep-layer shear appears to be very weak, but model
soundings suggest some mid-layer shear may be responsible for the
current structure. This shear could lessen by early next week,
allowing for slow intensification to begin in an environment that
should otherwise support strengthening. The NHC forecast is very
near the intensity model consensus, with the statistical-dynamical
models generally showing a faster rate of strengthening than the
dynamical ones.

The depression is moving westward, with an initial forward speed
near 13 kt. The depression should continue westward for the next
several days, slowing down slightly as the subtropical ridge to its
north weakens and moves eastward. After about 3 days, a mid- to
upper-level trough over the central Atlantic should begin to turn
the cyclone northwestward, and then northward by day 5, as long as
Seventeen intensifies as forecasted. The NHC track forecast is
heavily based on HCCA through the full forecast period. Confidence
in the track forecast is somewhat lower than normal based on the
model spread and uncertainty as to when the system will be
vertically deep enough to begin gaining more latitude, but nearly
all available ensemble guidance shows the same general evolution.


FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 15.6N 38.8W 30 KT 35 MPH
12H 24/0000Z 15.7N 41.0W 35 KT 40 MPH
24H 24/1200Z 15.8N 43.7W 35 KT 40 MPH
36H 25/0000Z 15.9N 46.2W 35 KT 40 MPH
48H 25/1200Z 16.2N 48.5W 40 KT 45 MPH
60H 26/0000Z 16.6N 50.2W 40 KT 45 MPH
72H 26/1200Z 17.1N 51.6W 45 KT 50 MPH
96H 27/1200Z 19.5N 54.0W 50 KT 60 MPH
120H 28/1200Z 23.0N 54.5W 55 KT 65 MPH

$$
Forecaster D. Zelinsky

[cycloneye]

Tropical Storm Philippe Advisory Number 2
NWS National Hurricane Center Miami FL AL172023
500 PM AST Sat Sep 23 2023

...DEPRESSION STRENGTHENS INTO TROPICAL STORM PHILIPPE..


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...15.6N 39.7W
ABOUT 1045 MI...1680 KM W OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES




Tropical Storm Philippe Discussion Number 2
NWS National Hurricane Center Miami FL AL172023
500 PM AST Sat Sep 23 2023

Overall, the structure of the cyclone hasn't changed significantly since this morning. Its low-level center is still displaced west of most of the associated deep convection. That said, satellite intensity estimates are generally a little higher than they were about 6 hours ago, ranging from about 30 to 35 kt. The intensity is set at 35 kt, in best agreement with the latest subjective TAFB Dvorak estimate and the objective UW-CIMSS DMINT and SATCON, making the system Tropical Storm Philippe.

Philippe is expected to maintain its general structure for the next couple of days, which should prevent it from substantially strengthening. While the intensity guidance is generally slightly higher than 6 h ago, the dynamical models remain in generally good agreement on the intensity forecast for the next few days. Beyond 72 h, Philippe will approach a mid- to upper-level trough, which could result in an increase of both upper-level difluence and deep-layer shear. Slight additional intensification is possible at that point, but no periods of significant strengthening are expected during the next 5 days. The official intensity forecast remains near the IVCN and HCCA intensity consensus aids.

The tropical storm continues to move westward, near 12 kt. This should generally continue for the next couple of days until Philippe approaches the aforementioned trough. At that point, as long as the tropical storm has strengthened slightly as expected, it should begin to turn northwestward, and then northward, influenced by the deeper-layer steering flow imparted by the trough. The official track forecast has been shifted slightly northeastward and slower compared to the previous one, and is close to the latest HCCA forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 15.6N 39.7W 35 KT 40 MPH
12H 24/0600Z 15.7N 41.6W 40 KT 45 MPH
24H 24/1800Z 15.9N 43.8W 40 KT 45 MPH
36H 25/0600Z 16.3N 46.0W 40 KT 45 MPH
48H 25/1800Z 16.7N 48.3W 45 KT 50 MPH
60H 26/0600Z 17.2N 50.0W 45 KT 50 MPH
72H 26/1800Z 18.0N 51.4W 50 KT 60 MPH
96H 27/1800Z 21.0N 53.5W 55 KT 65 MPH
120H 28/1800Z 24.0N 54.0W 60 KT 70 MPH

$$
Forecaster D. Zelinsky

[cycloneye]

BULLETIN
Tropical Storm Philippe Advisory Number 3
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Sat Sep 23 2023

...PHILIPPE MOVING WESTWARD...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.4N 40.9W
ABOUT 1125 MI...1810 KM W OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 265 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES


Tropical Storm Philippe Discussion Number 3
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Sat Sep 23 2023

Philippe is still a disorganized tropical storm. Geostationary
satellite imagery shows that deep convection is displaced to the northeast of the low-level center. Recent satellite-derived wind data revealed that the surface circulation is still elongated and winds in the southwest quadrant are quite weak. The initial intensity is held at 35 kt for this advisory, based on the ASCAT observations.

The tropical storm is moving westward at an estimate 12 kt. This general motion should continue for the next two days, as Philippe moves along the south side of a mid-level ridge. By 60 h, the storm should gradually turn to the west-northwest and northwest as it reaches a weakness in the ridge. The latest track forecast is similar to the previous advisory through day 3, and has shifted to the west and slightly slower at days 4 and 5.

Model guidance suggests Philippe should gradually organize and thus slowly strengthen in the next few days. This is possibly due to some mid-level vertical wind shear and upstream dry air. Beyond day 3, Philippe is expected to approach a mid- to upper-level trough, that should increase deep-layer vertical wind shear, but could also increase upper-level difluence. The intensity guidance generally favors some slight intensification during this period. The latest NHC forecast is similar to the previous advisory, and lies slightly above the consensus aid, IVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 24/0300Z 15.4N 40.9W 35 KT 40 MPH
12H 24/1200Z 15.5N 42.6W 40 KT 45 MPH
24H 25/0000Z 15.9N 44.8W 40 KT 45 MPH
36H 25/1200Z 16.3N 47.1W 40 KT 45 MPH
48H 26/0000Z 16.7N 49.1W 45 KT 50 MPH
60H 26/1200Z 17.4N 50.7W 45 KT 50 MPH
72H 27/0000Z 18.3N 52.0W 50 KT 60 MPH
96H 28/0000Z 21.2N 53.9W 55 KT 65 MPH
120H 29/0000Z 23.5N 54.5W 60 KT 70 MPH

$$
Forecaster Bucci

[cycloneye]

Tropical Storm Philippe Discussion Number 4
NWS National Hurricane Center Miami FL AL172023
500 AM AST Sun Sep 24 2023

Philippe is still trying to become better organized this morning.
There continues to be burst within the convection with very cold
cloud tops to -80 degrees Celsius. However, the convection remains
displaced to the northeast of the estimated low-level center. An
ASCAT pass that arrived just after the previous advisory revealed
winds on the northeast side of the system were near 40 kt.
Subjective satellite Dvorak estimates for this cycle from TAFB and
SAB were T3.0/T2.5, respectively. Using a blend of these estimates
and the scatterometer satellite-derived winds, the intensity for
this advisory is raised to 40 kt.

The system is moving westward at an estimated motion of 280/8 kt.
Philippe should continue westward fro the next couple of days,
steered along the southern side of a mid-level ridge. In about 2 to
3 days, a weakness in the ridge will develop and the tropical storm
should gradually turn west-northwest and then northwest. Models
have continued to slow the forward motion of Philippe towards the
end of the forecast period, and the NHC track forecast was adjusted
accordingly. The NHC track forecast lies near the corrected
consensus aids throughout the period, with a slight nudge to the
left of the previous track.

Models depict that Philippe will take some time to get organized due
to mid-level vertical wind shear and some drier mid-level RH values.
This will lead to only slow strengthening the next few days. In
about 3 days, as Philippe approaches a mid-upper level trough,
deep-layer vertical wind shear is forecast to increase but
upper-level divergence should increase over the system as well. The
guidance continues to favor some additional strengthen through the
end of the forecast period. The NHC intensity forecast is similar to
the previous advisory.


FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 15.6N 41.4W 40 KT 45 MPH
12H 24/1800Z 15.9N 43.1W 40 KT 45 MPH
24H 25/0600Z 16.3N 45.3W 45 KT 50 MPH
36H 25/1800Z 16.7N 47.5W 45 KT 50 MPH
48H 26/0600Z 17.3N 49.2W 45 KT 50 MPH
60H 26/1800Z 18.1N 50.9W 50 KT 60 MPH
72H 27/0600Z 19.2N 52.4W 50 KT 60 MPH
96H 28/0600Z 22.4N 54.4W 55 KT 65 MPH
120H 29/0600Z 24.2N 55.4W 60 KT 70 MPH

$$
Forecaster Kelly

[cycloneye]

Tropical Storm Philippe Discussion Number 5
NWS National Hurricane Center Miami FL AL172023
1100 AM AST Sun Sep 24 2023

Philippe is a challenging tropical cyclone to analyze this morning.
On one hand, the overall satellite presentation has improved since
yesterday, and a 0907Z SSMIS microwave pass shows a possible
mid-level eye. Yet the 1-min GOES16 imagery reveals a weak
low-level swirl southwest of the main convective blob, and ASCAT-B
near 12Z showed a disorganized inner core with less wind than one
might expect (albeit very contaminated with rain). Overall,
intensity estimates have risen since the last advisory, so the
initial wind speed is set to 45 kt, similar to the TAFB/SAB values,
but this should be considered fairly uncertain.

Little change in intensity is forecast with the storm during the
next couple of days as increasing shear is forecast to otherwise
counteract a conducive environment. There are a variety of
solutions after that point, with some models showing a stronger
Philippe after finding a lower-shear environment, while others
suggesting that the storm succumbs to the shear from an
upper-level trough. There are no easy answers here with moderate
shear cases in high SST/moisture conditions well known to have
higher errors due to an inherent lack of predictability. The new
forecast splits the difference in the model guidance, lying near
the consensus and the previous forecast, and we will just have to
see if a trend emerges for the eventual intensity of Philippe.

The long-term motion of the storm is westward or 280/10 kt. The
subtropical ridge to the north of Philippe is forecast to gradually
weaken and slide eastward in a day or two, allowing the tropical
storm to move more west-northwestward and northwestward by the
middle of the week. Uncertainty grows after that point, with the
track seemingly dependent on the intensity. A stronger system
would probably turn northward, like the GFS/HWRF/HMON models, while
a weaker one, like the UKMET/ECMWF solutions, would take a left
turn under the low-level subtropical ridge. For now, little change
was made to the long-range forecast given all of the uncertainty.


FORECAST POSITIONS AND MAX WINDS

INIT 24/1500Z 16.2N 41.7W 45 KT 50 MPH
12H 25/0000Z 16.5N 43.3W 45 KT 50 MPH
24H 25/1200Z 16.9N 45.6W 45 KT 50 MPH
36H 26/0000Z 17.4N 47.8W 45 KT 50 MPH
48H 26/1200Z 18.0N 49.7W 45 KT 50 MPH
60H 27/0000Z 18.9N 51.0W 50 KT 60 MPH
72H 27/1200Z 20.0N 52.5W 50 KT 60 MPH
96H 28/1200Z 22.5N 54.5W 55 KT 65 MPH
120H 29/1200Z 24.0N 55.5W 55 KT 65 MPH

$$
Forecaster Blake

[cycloneye]

Tropical Storm Philippe Discussion Number 6
NWS National Hurricane Center Miami FL AL172023
500 PM AST Sun Sep 24 2023

Microwave and satellite data indicate that the center of Philippe
has re-formed to the northeast of earlier estimates. Overall, the
storm is reasonably well organized, with convection near the center
and a large central dense overcast. Intensity estimates are about
the same as the last cycle, so the initial wind speed remains 45 kt.

There aren't many changes to the intensity prediction reasoning in
this advisory. Increasing shear is forecast to otherwise counteract
a conducive environment, leading to little net change with Philippe
during the next couple of days. Afterwards, models are in quite
poor agreement on if the shear continues to rise to strong levels,
which causes dissipation like the ECMWF, or if it becomes more
manageable to allow for further intensification, similar to the
GFS's hurricane forecast at day 5. There are no obvious clues to
the correct solution, and this is probably a very difficult forecast
due to the feedback of Philippe's track affecting intensity, in
addition to the inherent challenges of moderate shear cases. Thus,
little change was made to the intensity forecast, which lies near
the overall model and corrected-consensus aids.

The storm appears to be moving west-northwestward or 290/10 kt. The
subtropical ridge to the north of Philippe is forecast to gradually
weaken and slide eastward in a day or two, allowing the tropical
storm to move more west-northwestward and northwestward by the
middle of the week. Uncertainty is large after that point, with the
track very likely also dependent on the intensity and vortex depth,
and the GFS and ECMWF models are on the opposite sides of the
guidance envelope. The long-range guidance has shifted a bit
westward on this cycle, and the new forecast follows that trend.
However, this forecast should be considered low-confidence in both
track and intensity.


FORECAST POSITIONS AND MAX WINDS

INIT 24/2100Z 16.8N 42.5W 45 KT 50 MPH
12H 25/0600Z 17.3N 44.1W 45 KT 50 MPH
24H 25/1800Z 17.8N 46.4W 45 KT 50 MPH
36H 26/0600Z 18.2N 48.6W 45 KT 50 MPH
48H 26/1800Z 18.8N 50.4W 45 KT 50 MPH
60H 27/0600Z 19.7N 52.0W 50 KT 60 MPH
72H 27/1800Z 21.0N 53.5W 50 KT 60 MPH
96H 28/1800Z 23.0N 55.5W 55 KT 65 MPH
120H 29/1800Z 25.0N 57.0W 60 KT 70 MPH

$$
Forecaster Blake

[cycloneye]

Tropical Storm Philippe Discussion Number 7
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Sun Sep 24 2023

Another prominent convective burst has formed over Philippe (the
storm) since the prior advisory. However, indications from the last
received microwave imagery (a 2033 UTC F-16 SSMIS pass) suggest that
the large cirrus plume produced is mainly the product of a cluster
of cells in the down-shear quadrants of the storm, with little
indication of improved organization with the tropical cyclone. There
is also evidence of mid-level shear undercutting the outflow layer
to the west of the cyclone. Subjective Dvorak intensity
estimates from TAFB and SAB remain at T3.0/45-kt, and Philippe's
initial intensity this advisory is held at 45 kt, which is also
close to a mean D-MINT value associated with the above mentioned
microwave pass.

The intensity forecast for the next 2-3 days is tricky, as vertical
wind shear (especially mid-level shear under the outflow layer)
already appears to be keeping Philippe in check, and preventing the
deep convection from wrapping around the center. Neither the GFS or
ECMWF suggest this shear will abate much for at least the next 2-3
days. In fact the primary reason why the forecast was held steady
over this time span is that the cyclone will also continue
traversing anomalously warm 29C sea-surface temperatures, while
mid-level moisture stays about the same or increases some during
this time span. However, it would not be surprising to see some
weakening in the short-term either, as suggested by the
regional-hurricane models, particularly HMON and COAMPS-TC
forecasts. After 72 hours, assuming the storm begins to turn
poleward, there is some potential the storm start moving north of
this shear zone, where some gradual intensification could begin. The
intensity forecast is largely similar to the prior advisory, and is
closest to the HFIP Corrected Consensus Approach (HCCA).

Philippe continues to move west-northwestward at 290/12 kt. For the
next day or so, the guidance is in fairly good agreement on this
motion continuing as an extensive mid-level ridge centered north of
the cyclone remains in place. Beyond that time span, however, is
where the guidance diverges quite dramatically. While most of the
guidance agrees a large weakness will appear in the mid-level
ridging to the north of Philippe, whether or not the system is able
to turn northward into this weakness is largely a byproduct of how
vertically deep the cyclone is able to remain. Assuming the storm
remains at least somewhat vertically coherent, the track forecast
does show a turn northwest and then north-northwest by the end of
the 5-day forecast. However, the spread in the guidance at this time
period remains notable, with stronger solutions turning more north
or even northeast, while weaker (and solutions that dissipate
Philippe) maintaining a west-northwest heading. The NHC track
forecast continues to split the difference between these extremes,
and lies close to both the simple and corrected consensus aids. As
discussed previously, this remains a low confidence track and
intensity forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 17.1N 43.3W 45 KT 50 MPH
12H 25/1200Z 17.6N 45.0W 45 KT 50 MPH
24H 26/0000Z 18.1N 47.3W 45 KT 50 MPH
36H 26/1200Z 18.5N 49.2W 45 KT 50 MPH
48H 27/0000Z 19.3N 51.0W 45 KT 50 MPH
60H 27/1200Z 20.4N 52.7W 50 KT 60 MPH
72H 28/0000Z 21.6N 54.0W 50 KT 60 MPH
96H 29/0000Z 23.4N 55.9W 55 KT 65 MPH
120H 30/0000Z 25.5N 57.0W 55 KT 65 MPH

$$
Forecaster Papin

[cycloneye]

Tropical Storm Philippe Discussion Number 8
NWS National Hurricane Center Miami FL AL172023
500 AM AST Mon Sep 25 2023

The satellite appearance of Philippe has remained steady overnight.
Burst of deep convection, with cold cloud tops to -80 C, continue
from time to time within the overall convective plume. An AMSR
microwave pass depicts that the convection remains displaced to the
east of the low-level center, with the system still lacking
organization. Philippe is struggling to become better organized due
to the strong mid-level shear impacting the system. Subjective
Dvorak intensity estimates from TAFB and SAB remain at T3.0/45-kt
this cycle, and the initial intensity is held at 45 kt.

Philippe will continue to be in an environment with moderate to
strong mid-level shear, which will limit the overall organization of
the system. The storm is traversing fairly warm sea surface
temperatures around 29C and favorable mid-level RH values the next
few days. Given these mixed parameters and lack of organization, the
NHC forecast calls for Philippe to remain fairly steady with the
potential for some slow strengthening by the end of the period.
However, there remains uncertainty in the intensity forecast given
the guidance envelope. The ECMWF suggest the system remains steady
or may even weaken, while the GFS depicts strengthening with the
system moving far enough north into a lower shear environment. The
intensity forecast is similar to the previous, and is closest to the
IVCN and HCCA consensus aids.

The system is moving west-northwest at an estimated motion of 285/9
kt. Philippe should continue west-northwestward over the next day or
two, steered along the southern side of a mid-level ridge. In about
2 days, all models depict a weakness developing in the ridge, but
the track guidance diverges quite drastically, and it is directly
related to the intensity of the system. A deeper, stronger system,
like the GFS depicts, will feel the weakness in the ridge and curve
the system faster on a more northwestward track. However, a weaker,
shallow cyclone, like the ECMWF depicts, will cause the system to
continue on a west-northwestward or even westward track. The NHC
track forecast continues to be in the middle of the guidance, and
lies close to both the simple and corrected consensus aids. This
remains a low confidence track and intensity forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 25/0900Z 17.4N 43.9W 45 KT 50 MPH
12H 25/1800Z 17.8N 45.7W 45 KT 50 MPH
24H 26/0600Z 18.3N 47.9W 45 KT 50 MPH
36H 26/1800Z 19.0N 49.9W 45 KT 50 MPH
48H 27/0600Z 20.0N 51.8W 45 KT 50 MPH
60H 27/1800Z 21.2N 53.3W 50 KT 60 MPH
72H 28/0600Z 22.4N 54.5W 50 KT 60 MPH
96H 29/0600Z 24.0N 56.0W 55 KT 65 MPH
120H 30/0600Z 25.5N 57.0W 55 KT 65 MPH

$$
Forecaster Kelly

[cycloneye]

Tropical Storm Philippe Discussion Number 9
NWS National Hurricane Center Miami FL AL172023
1100 AM AST Mon Sep 25 2023

Visible satellite images indicate that Philippe has become less
organized this morning. The low-level center has become fully
exposed with all of the deep convection now displaced well to the
east of the center. The initial wind speed is held at 45 kt, in
agreement with most of the satellite intensity estimates.

Philippe is currently experiencing about 20-25 kt of
west-southwesterly vertical wind shear. Both the GFS- and
ECMWF-based SHIPS models show the vertical wind shear increasing
even more during the next few days. These hostile winds and dry air
entrainment should cause Philippe to continue to struggle throughout
the forecast period. There is some spread in the guidance with a
couple of models showing slight strengthening and several of the
models showing slight weakening. Based on the guidance and expected
continued shear, the new forecast is lower than the previous one and
shows no change in strength during the next several days.

Geostationary and microwave satellite images indicate that Philippe
has jogged to the left this morning. Smoothing through this wobble
yields an initial motion of 280/11 kt. A turn back to the
west-northwest is expected by tonight, followed by a northwestward
motion in a couple of days as Philippe moves toward a weakness in
the subtropical ridge. There is a vast amount of spread in the
track models this morning with the GFS and its ensemble mean on the
far right side of the guidance envelope and the ECMWF on the left
side. An examination of the GFS model fields suggests that the
model is showing a vortex that is likely too vertically aligned, and
not representative of the environmental conditions. Therefore,
that model is considered an outlier for the time being. The new
NHC track forecast is adjusted to the left toward the various
consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT 25/1500Z 17.3N 45.5W 45 KT 50 MPH
12H 26/0000Z 17.6N 47.2W 45 KT 50 MPH
24H 26/1200Z 18.1N 49.2W 45 KT 50 MPH
36H 27/0000Z 18.9N 51.2W 45 KT 50 MPH
48H 27/1200Z 19.9N 52.9W 45 KT 50 MPH
60H 28/0000Z 21.1N 54.2W 45 KT 50 MPH
72H 28/1200Z 22.1N 55.4W 45 KT 50 MPH
96H 29/1200Z 23.7N 56.9W 45 KT 50 MPH
120H 30/1200Z 24.6N 57.9W 45 KT 50 MPH

$$
Forecaster Cangialosi/Konarik

[cycloneye]

BULLETIN
Tropical Storm Philippe Advisory Number 10
NWS National Hurricane Center Miami FL AL172023
500 PM AST Mon Sep 25 2023

...PHILIPPE WEAKENS A LITTLE...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...17.3N 46.7W
ABOUT 1080 MI...1740 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES




Tropical Storm Philippe Discussion Number 10
NWS National Hurricane Center Miami FL AL172023
500 PM AST Mon Sep 25 2023

Visible satellite images continue to show Philippe with a fully
exposed center far removed to the west of all of the deep
convection. The continued disorganized appearance suggests at least
some weakening has occurred, and satellite intensity estimates
concur. Thus, the wind speed has been lowered to 40 kt.

Philippe continues to be impacted by 20-25 kt of deep-layer
west-southwesterly vertical wind shear. This wind shear is forecast
by both GFS- and ECMWF-based SHIPS models to persist or even
increase further during the next few days. This unfavorable shear
combined with dry air entrainment will hinder strengthening through
the forecast period. A few models suggest some slight increase in
intensity in the 48- to 72-hour time frame due to warmer sea-surface
temperatures, but other environmental factors will remain negative.
The new forecast indicates no change in strength over the next
several days, with some weakening toward the end of the forecast
period.

The exposed low-level center of Philippe has been moving west today
with a slight increase in forward motion this afternoon. The system
should veer toward the west-northwest tonight then turn northwest by
mid-week as Philippe moves toward a weakness in the subtropical
ridge. By late week, this weakness becomes less pronounced and the
overall steering flow diminishes. The forecast track at the end of
the period therefore slows and curves back toward the
west-northwest. There remains considerable spread in the track
models this afternoon, with the GFS and its ensemble members
representing far rightward outliers. With the ongoing motion to the
west and a leftward shift of the overall guidance output, the NHC
forecast track has been adjusted slightly west, especially beyond 72
hours due to the aforementioned steering flow changes.


FORECAST POSITIONS AND MAX WINDS

INIT 25/2100Z 17.3N 46.7W 40 KT 45 MPH
12H 26/0600Z 17.7N 48.5W 40 KT 45 MPH
24H 26/1800Z 18.4N 50.4W 40 KT 45 MPH
36H 27/0600Z 19.3N 52.3W 40 KT 45 MPH
48H 27/1800Z 20.4N 54.0W 40 KT 45 MPH
60H 28/0600Z 21.6N 55.4W 40 KT 45 MPH
72H 28/1800Z 22.2N 56.3W 40 KT 45 MPH
96H 29/1800Z 22.9N 57.7W 40 KT 45 MPH
120H 30/1800Z 23.4N 59.5W 35 KT 40 MPH

$$
Forecaster Konarik/Cangialosi

[cycloneye]

BULLETIN
Tropical Storm Philippe Advisory Number 11
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Mon Sep 25 2023

...PHILIPPE CONTINUES TO STRUGGLE AGAINST SHEAR BUT SATELLITE
WIND DATA SHOWS HIGHER WINDS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.6N 47.8W
ABOUT 1005 MI...1620 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1001 MB...29.56 INCHES




Tropical Storm Philippe Discussion Number 11
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Mon Sep 25 2023

There have not been many changes to the appearance of Philippe
tonight. The low-level circulation continues to be primarily exposed
to the west of a rather misshapen area of deep convection. While
there are a few convective cells that have attempted to redevelop
closer to the circulation center, the storm remains disrupted by
20-30 kt of westerly vertical wind shear. While subjective and
objective satellite intensity estimates continue to gradually
decrease, earlier GOES-16 1-minute meso sector low-level derived
motion winds north of Philippe were in the 50-60 kt range, which
typically would support somewhat higher winds. In addition, a
recently arriving ASCAT-C pass caught the eastern side of the
circulation, revealing peak winds in the 40-45 kt range. Therefore,
the initial intensity is adjusted to 45 kt for this advisory.

Despite the slightly higher initial intensity, Philippe's future
prospects appear increasingly dim (as a tropical cyclone), as the
current shear affecting the system is not expected to abate. In
fact, this shear may increase further after 48 hours. Because the
storm will still continue to traverse warm 29-30C sea-surface
temperatures, the storm is likely to continue generating convective
bursts east of the center for the majority of the forecast period.
However, it appears increasingly likely the shear will not be able
to be overcome, and the updated NHC intensity forecast now shows the
storm on a slow decline, ending with it becoming a remnant low
sometime in the day 4-5 time frame. This forecast is in good
agreement with the consensus aids, with remnant low status
occuring roughly when the ECMWF shows the system stopping to
produce organized convection.

Philippe appears to have resumed a more west-northwestward motion at
285/10 kt. Compared to 24 hours ago, the guidance has started to
come into better agreement that the storm should maintain a general
west-northwestward motion for the next 48-72 hours, not really
feeling the mid-level weakness developing to its north as it
gradually becomes more vertically shallow. The biggest change
compared to the prior advisory is showing a turn more westward by
the end of the forecast as the system becomes primarily steered by
the more east-to-west oriented low-level ridging. This leftward
adjustment to the track forecast is mainly in response to similar
leftward shifts in both the GFS and ECMWF ensemble guidance that
have shifted to weaker solutions steered by the low-level flow. The
NHC track lies roughly in between the reliable consensus aids (TVCN,
HCCA) and the ECMWF and its ensemble mean, which remain on the south
and west side of the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 26/0300Z 17.6N 47.8W 45 KT 50 MPH
12H 26/1200Z 18.0N 49.4W 45 KT 50 MPH
24H 27/0000Z 18.8N 51.4W 40 KT 45 MPH
36H 27/1200Z 19.8N 53.1W 40 KT 45 MPH
48H 28/0000Z 20.8N 54.6W 35 KT 40 MPH
60H 28/1200Z 21.5N 56.0W 35 KT 40 MPH
72H 29/0000Z 22.0N 57.4W 35 KT 40 MPH
96H 30/0000Z 22.0N 59.4W 30 KT 35 MPH
120H 01/0000Z 22.0N 61.4W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin

[cycloneye]

Tropical Storm Philippe Discussion Number 12
NWS National Hurricane Center Miami FL AL172023
500 AM AST Tue Sep 26 2023

West-southwesterly vertical wind shear, associated with an
upper-level low near 26N 50W, continues to affect Philippe. The
low-level center of the tropical cyclone is located near the
western edge of an area of rather disorganized deep convection.
Some sporadic convection has been redeveloping nearer to the center
of the system, but overall Philippe's cloud pattern remains
disheveled in appearance and lacks banding features. The current
intensity estimate is kept at 45 kt in deference to the earlier
scatterometer data. However, subjective and objective Dvorak
intensity estimates are somewhat lower.

The global models indicate that the vertical shear over Philippe
is not likely to abate significantly during the forecast period,
with upper-tropospheric westerlies dominating the flow to the north
and northeast of the Greater Antilles through 120 hours. Also, the
model guidance indicates that Philippe will be encountering a
somewhat drier low- to mid-level air mass during the next several
days. These environmental factors should lead to gradual weakening,
and thus Philippe is forecast to become a depression and then a
remnant low in 3 and 5 days, respectively. This is in good
agreement with the corrected consensus intensity model, HCCA,
guidance.

Over the past day or so, the storm has been moving westward to
west-northwestward and the current motion estimate is 285/11 kt. A
weak mid-level ridge is expected to be maintained to the north
of Philippe for the next few days, which is likely to keep steering
the cyclone on a generally west-northwestward track. Later in the
forecast period, Philippe should be a weaker, shallower system and
move on a mainly westward heading, following the low-level easterly
flow. The official track forecast is similar to the previous NHC
track, only a little to the left and slightly faster in 3-5 days.
This lies between the model consensus and the latest ECMWF
prediction, which is even faster and a little farther south.


FORECAST POSITIONS AND MAX WINDS

INIT 26/0900Z 17.7N 49.0W 45 KT 50 MPH
12H 26/1800Z 18.2N 50.4W 45 KT 50 MPH
24H 27/0600Z 19.1N 52.1W 45 KT 50 MPH
36H 27/1800Z 20.1N 53.9W 45 KT 50 MPH
48H 28/0600Z 21.0N 55.4W 40 KT 45 MPH
60H 28/1800Z 21.6N 56.9W 40 KT 45 MPH
72H 29/0600Z 21.9N 58.2W 35 KT 40 MPH
96H 30/0600Z 21.8N 60.9W 30 KT 35 MPH
120H 01/0600Z 21.8N 63.6W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Pasch

[cycloneye]

Tropical Storm Philippe Discussion Number 13
NWS National Hurricane Center Miami FL AL172023
1100 AM AST Tue Sep 26 2023

Philippe continues to struggle due to strong west-southwesterly
shear associated with a mid- to upper-level low to its northwest.
The low-level center is completely exposed and deep convection
remains well removed to the east of the center. The latest
satellite intensity estimates range from 30 to 42 kt, and based on
that data, the initial wind speed is nudged downward to 40 kt.

The strong shear is not expected to let up over the next several
days, which should keep the storm asymmetric and weak. A
combination of the shear and dry air entrainment should lead to a
gradual decay, and simulated satellite images from the GFS and ECMWF
models suggest that Philippe will likely degenerate into a remnant
low in 3 or 4 days. The NHC intensity forecast lies near the middle
of the guidance envelope and now shows the system becoming a
remnant low by day 4.

Philippe continues to move westward, and it has not gained much
latitude over the past 24 hours due to its sheared structure.
Based on the previous track, the expected asymmetric structure, and
the new model guidance, the NHC track forecast is again shifted to
the left as Philippe is expected to continue to move in the low- to
mid-level flow. This forecast lies on the southern side of the
guidance envelope, in best agreement with the ECMWF model.


FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 17.3N 50.3W 40 KT 45 MPH
12H 27/0000Z 17.9N 51.6W 40 KT 45 MPH
24H 27/1200Z 18.9N 53.4W 40 KT 45 MPH
36H 28/0000Z 19.8N 55.0W 40 KT 45 MPH
48H 28/1200Z 20.7N 56.5W 35 KT 40 MPH
60H 29/0000Z 21.2N 58.0W 35 KT 40 MPH
72H 29/1200Z 21.2N 59.8W 30 KT 35 MPH
96H 30/1200Z 21.2N 62.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 01/1200Z 21.3N 65.1W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Cangialosi

[cycloneye]

Tropical Storm Philippe Discussion Number 14
NWS National Hurricane Center Miami FL AL172023
500 PM AST Tue Sep 26 2023

Philippe remains a strongly sheared and poorly organized tropical
storm. The low-level center continues to pull away from the
associated deep convection and is now located about 100 n
mi west of a small area of thunderstorms. In fact, the system
barely meets the convective criteria of a tropical cyclone.
Despite the ragged satellite appearance, the initial intensity is
held at 40 kt based on partial ASCAT data that showed a patch of
tropical-storm-force winds well east of the center earlier today.

The models are in agreement that strong shear will continue to
affect Philippe during the next several days, which in combination
with dry air entrainment should cause gradual weakening despite
its passage over warm SSTs. Simulated satellite images from the
GFS and ECMWF models show Philippe losing all of its deep
convection in a few days, and the NHC forecast continues to show
Philippe becoming a remnant low by day 4. However, it would not be
surprising if the system becomes a remnant low or opens into a
trough sooner than that.

Philippe has not gained any latitude since this time yesterday and
all of the models have had a notable north bias during that time
period. Based on recent trends and since Philippe is expected to
stay a decoupled and weak system moving in the low-level flow,
another shift to the left has been made in this forecast. This
prediction lies near the southern side of the model guidance
envelope.


FORECAST POSITIONS AND MAX WINDS

INIT 26/2100Z 17.1N 51.3W 40 KT 45 MPH
12H 27/0600Z 17.3N 52.7W 40 KT 45 MPH
24H 27/1800Z 18.4N 54.5W 35 KT 40 MPH
36H 28/0600Z 19.2N 56.1W 35 KT 40 MPH
48H 28/1800Z 19.7N 57.9W 35 KT 40 MPH
60H 29/0600Z 20.0N 59.3W 30 KT 35 MPH
72H 29/1800Z 20.1N 61.0W 30 KT 35 MPH
96H 30/1800Z 20.2N 64.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 01/1800Z 20.3N 67.8W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Cangialosi

[cycloneye]

BULLETIN
Tropical Storm Philippe Advisory Number 15
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Tue Sep 26 2023

...PHILIPPE EXPECTED TO SLOWLY WEAKEN OVER THE NEXT SEVERAL DAYS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.4N 52.0W
ABOUT 730 MI...1180 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES




Tropical Storm Philippe Discussion Number 15
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Tue Sep 26 2023

After the previous advisory, there was a convective burst with cloud
tops as cold as -80C that formed near the circulation center. More
recently, this burst has been waning in intensity, and it would not
be surprising to see the vortex become exposed again shortly as
20-30 kt southwesterly vertical wind shear continues. While
subjective and objective intensity estimates continue to suggest a
weaker storm, a helpful 0015 UTC ASCAT-B pass still showed a large
region of 35-40 kt winds in the northeastern side of the
circulation, in fact requiring an expansion of the tropical storm
force winds in that quadrant. Based primarily on the scatterometer
data, Philippe's intensity remains 40 kt for this advisory.

The intensity forecast appears rather straightforward. The current
vertical wind shear over Philippe is expected to continue through
most of the forecast period, helping to import drier air into the
circulation, that should prevent additional convective bursts from
organizing the system. By 72 hours, both the GFS and ECMWF are in
agreement that Philippe should no longer have organized deep
convection, which is when the forecast shows the system becoming a
post-tropical remnant low. As mentioned previously, this could
happen sooner than forecasted given the unfavorable environment.

After moving south of due west earlier today, Philippe appears to
have resumed a north of due west heading, estimated at 280/10 kt.
The track guidance is in good agreement on this motion continuing
with a bend westward in 36-48 hours as the cyclone becomes
primarily steered by the low-level flow. The latest NHC track
forecast remains along or just south of the model guidance consensus
aids, and is between the GFS and ECMWF solutions.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0300Z 17.4N 52.0W 40 KT 45 MPH
12H 27/1200Z 17.9N 53.4W 40 KT 45 MPH
24H 28/0000Z 18.8N 55.2W 35 KT 40 MPH
36H 28/1200Z 19.4N 56.8W 35 KT 40 MPH
48H 29/0000Z 19.8N 58.3W 35 KT 40 MPH
60H 29/1200Z 20.0N 59.8W 30 KT 35 MPH
72H 30/0000Z 20.0N 61.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 01/0000Z 20.1N 64.7W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 02/0000Z 20.2N 67.0W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Papin

[cycloneye]

Tropical Storm Philippe Discussion Number 16
NWS National Hurricane Center Miami FL AL172023
500 AM AST Wed Sep 27 2023

Philippe continues to be a disorganized tropical cyclone.
Satellite imagery shows a cloud pattern consisting of bursting deep
convection in an amorphous-looking blob just east of the estimated
center with a few areas of convection farther to the east and
southeast. Although there was some evidence earlier of a
convective band over the eastern periphery of the circulation, that
feature has since broken up into less-organized patches of showers
and thunderstorms. The current intensity estimate is held at 40 kt
based on earlier scatterometer measurements. However, subjective
and objective Dvorak intensity estimates suggest a weaker storm.

Philippe is expected to remain in a sheared environment, and
ingesting drier low- to mid-level air, over the next few days.
Wind fields from both the ECMWF and GFS models show Philippe's
circulation weakening below tropical storm strength around 48 hours
and beyond. Simulated satellite imagery from those models also
depict the system as lacking sufficient organized deep convection to
be considered a tropical cyclone while it approaches the northern
Leeward Islands. The official intensity forecast, like the previous
one, shows Philippe degenerating into a remnant low pressure area
around 72 hours.

The cyclone continues on a mainly westward heading at around 280/10
kt. Philippe is currently being steered by the flow to the south
of a weak mid-level anticyclone, and is expected to move
west-northwestward on the southwest side of this high during the
next couple of days. In the latter part of the forecast period,
the weakening and increasingly shallow system should turn toward
the west-southwest following the low-level trade winds. The
official track forecast has again been shifted a little southward in
3-5 days, following the TVCN consensus solution.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0900Z 17.6N 52.7W 40 KT 45 MPH
12H 27/1800Z 18.4N 54.1W 40 KT 45 MPH
24H 28/0600Z 19.1N 55.8W 35 KT 40 MPH
36H 28/1800Z 19.6N 57.1W 35 KT 40 MPH
48H 29/0600Z 19.6N 58.6W 35 KT 40 MPH
60H 29/1800Z 19.5N 60.3W 30 KT 35 MPH
72H 30/0600Z 19.4N 62.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 01/0600Z 19.0N 64.4W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 02/0600Z 19.0N 66.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Pasch

[cycloneye]

Tropical Storm Philippe Discussion Number 17
NWS National Hurricane Center Miami FL AL172023
1100 AM AST Wed Sep 27 2023

Visible, infrared and microwave imagery depicts that Philippe is a
slightly better organized system this morning. A burst of deep
convection continues near and east of the center. In addition,
earlier AMSR and SSMI/S microwave passes show that a convective
band has been developing on the eastern side of the circulation.
However, visible satellite images within the past hour depict that
the low-level center is becoming partially exposed on the western
edge of the convection. Subjective and objective satellite
intensity estimates have increased this cycle, with a TAFB Dvorak
data-T number of 3.0, 45 kt. Given the developing banding feature
and satellite intensity estimates, the initial intensity is raised
to 45 kt for this advisory. This is also in agreement with a
recent ASCAT-B pass.

Philippe is expected to remain in a sheared environment
over the next few days. However, the GFS SHIPS vertical wind shear
forecast shows a slight decrease, which may allow to the storm to
withhold convection near the low-level center a little longer than
what was previously anticipated. Philippe is forecast to move into a
slightly drier mid-level airmass in a few days, which may also
inhibit the overall convective pattern. Some slight fluctuations in
intensity may occur due to the pulsing convective nature of the
system during the next few days, with an overall slow weakening
trend later this weekend. The NHC intensity forecast was raised
slightly given the initial higher intensity. There remains
uncertainty in the intensity forecast and it is possible Philippe
maintains its tropical cyclone status as it reaches the northern
Leeward Islands.

The storm has not gained much latitude this morning and continues to
move mainly westward at around 280/8 kt. Philippe is currently
being steered by the flow around a weak mid-level ridge and is
expected to move west-northwestward over the next couple of days.
In the latter part of the forecast period, the weakening and shallow
system should turn toward the west-southwest. The track forecast is
highly dependent on the intensity forecast, however. The official
track forecast has again been shifted southward in 3-5 days, but
not as far south as the consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT 27/1500Z 17.5N 53.7W 45 KT 50 MPH
12H 28/0000Z 18.0N 54.7W 45 KT 50 MPH
24H 28/1200Z 18.6N 56.1W 45 KT 50 MPH
36H 29/0000Z 19.0N 57.8W 40 KT 45 MPH
48H 29/1200Z 19.0N 59.5W 40 KT 45 MPH
60H 30/0000Z 18.9N 60.8W 35 KT 40 MPH
72H 30/1200Z 18.7N 62.2W 35 KT 40 MPH
96H 01/1200Z 18.4N 64.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 02/1200Z 18.1N 66.9W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kelly

[cycloneye]

Tropical Storm Philippe Discussion Number 18
NWS National Hurricane Center Miami FL AL172023
500 PM AST Wed Sep 27 2023

Philippe's convection continues to oscillate this afternoon. Shortly
after the previous advisory, the convection waned and has become
less organized. An ASCAT-C pass showed that the center of the system
has become more ill-defined, with the low-level center difficult to
pinpoint this afternoon. Convection continues to redevelop back to
the east, with the expected mean center on the west side of the
convection. This was further supported by an AMSR microwave
overpass depicting and overall lack of organization. Subjective
Dvorak data-T numbers have come down with the current intensity
estimates remaining at 3.0. Given the earlier ASCAT-B pass and the
CI intensity estimates, the initial intensity will is held at 45
kt, but this could be generous.

This is a fairly complicated intensity and track forecast. Philippe
is in a sheared environment, and currently lacks organization. The
system is forecast to move into a slightly drier mid-level airmass
in a few days, which may also inhibit the overall convective
pattern. Some slight fluctuations in intensity may occur due to the
pulsing convective nature of the system during the next few days,
with an overall slow weakening trend later this weekend. There
remains uncertainty in the intensity forecast and it is possible
Philippe maintains its tropical cyclone status as it reaches the
northern Leeward Islands, or the system could weaken and open into
a trough.

The estimated motion is west-northwestward at 4 kt. Philippe is
currently being steered by the flow around a weak mid-level ridge
and is expected to move west-northwestward over the next couple of
days. In the latter part of the forecast period, a weakening and
shallow system should turn toward the west-southwest. There is
unusually large spread in the model guidance this cycle with the GFS
and ECMWF over 1100 miles apart on Day 5. The GFS is stronger and on
the right side, of the guidance envelope which has pulled the
consensus aids right as well. The ECMWF is weaker and on the left
side of the guidance. The track forecast is highly dependent on the
intensity forecast, however. The official track forecast is similar
to the previous forecast, just slower given the initial slower
motion, which is closest to the ECMWF.


FORECAST POSITIONS AND MAX WINDS

INIT 27/2100Z 17.7N 54.0W 45 KT 50 MPH
12H 28/0600Z 18.1N 55.1W 45 KT 50 MPH
24H 28/1800Z 18.6N 56.5W 40 KT 45 MPH
36H 29/0600Z 18.9N 57.7W 40 KT 45 MPH
48H 29/1800Z 18.9N 58.8W 40 KT 45 MPH
60H 30/0600Z 18.8N 60.0W 35 KT 40 MPH
72H 30/1800Z 18.7N 61.6W 35 KT 40 MPH
96H 01/1800Z 18.4N 64.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 02/1800Z 18.2N 66.3W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Kelly

[cycloneye]

Tropical Storm Philippe Discussion Number 19
NWS National Hurricane Center Miami FL AL172023
1100 PM AST Wed Sep 27 2023

Deep convection has persisted around the eastern portion of
Philippe's circulation this evening, however there is not much
evidence of curved bands. The low-level center may have reformed or
become slightly better defined just to the west of the main
convective mass since the previous advisory. There has been no
recent microwave imagery to gain a better look at the cyclone's
structure and scatterometer appears likely to miss the center this
evening. The latest subjective Dvorak intensity estimates were T3.0
(45 kt) and T2.5 (35 kt) from TAFB and SAB, respectively. The
initial intensity is held at 45 kt for this advisory, in deference
to the earlier scatterometer data and latest TAFB estimate.

The track forecast for Philippe remains quite complicated, and it is
very dependent on the future intensity and vertical depth of the
cyclone. The current disorganized structure of Philippe and its
present environment of moderate southwesterly shear is likely to
inhibit strengthening over the next couple of days. The main
question is whether Philippe weakens and becomes more vertically
shallow or if it maintains some vertical coherence during that time.
If it becomes vertically shallow, Philippe is likely to move
generally westward or west-southwestward within the low-level
steering flow. If it remains more vertically deep, the cyclone is
likely to move little as it remains to the southeast of a mid-level
ridge. Another complicating factor is a disturbance (AL91) to
Philippe's southeast. The latest GFS run moves that system close
enough to Philippe that binary interaction occurs between the two
systems. However this run appears to have initialized Philippe
stronger than it actually is, which may have led to the solution
where Philippe remains the dominate system. Meanwhile, the
ECMWF weakens Philippe and keeps more separation between the two
systems, taking a weaker Philippe westward or west-southwestward.
The NHC forecast currently favors the latter scenario, but there is
an unusually large amount of uncertainty in the track and intensity
forecast. In general, the guidance is a bit slower this cycle and
the NHC forecast has been adjusted accordingly. The new track
forecast is not as slow as the consensus aids, but is a blend
of the previous official forecast and the latest consensus models.
It would not be surprising if additional adjustments to the track
forecast are required in subsequent advisories.

As mentioned above, moderate southwesterly shear and a slightly
drier airmass ahead of Philippe are likely to inhibit significant
convective organization of the cyclone at least during the next day
or two. That is likely to cause some gradual weakening, and the NHC
intensity forecast follows that thinking and calls for the system to
weaken during that time. However, there is still a lot of
uncertainty as to whether Philippe weakens and becomes a remnant low
later in the period, or moves little and remains a tropical cyclone.
The latest forecast maintains continuity from the previous few
advisories and calls for Philippe to become a remnant low, but this
is a low confidence forecast.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0300Z 18.2N 54.5W 45 KT 50 MPH
12H 28/1200Z 18.7N 55.5W 45 KT 50 MPH
24H 29/0000Z 19.0N 56.6W 40 KT 45 MPH
36H 29/1200Z 19.0N 57.6W 40 KT 45 MPH
48H 30/0000Z 19.0N 58.6W 40 KT 45 MPH
60H 30/1200Z 18.7N 59.4W 35 KT 40 MPH
72H 01/0000Z 18.5N 60.3W 35 KT 40 MPH
96H 02/0000Z 18.5N 62.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 03/0000Z 18.5N 63.5W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown

[cycloneye]

Tropical Storm Philippe Discussion Number 20
NWS National Hurricane Center Miami FL AL172023
500 AM AST Thu Sep 28 2023

Philippe remains a disorganized, sheared storm. Deep convection
has continued through the night to the southeast of the estimated
low-level center. Imagery from a 0525 UTC satellite microwave pass
showed a decent curved band associated with this convection in the
89 GHz channel. Unfortunately, ASCAT missed the storm entirely.
The initial intensity is held at 45 kt for this advisory, closest
to the TAFB Dvorak estimate.

There is still low confidence in Philippe's track forecast. As
stated in previous advisories, the future location of the storm is
closely linked to its structure and intensity. Should Philippe
remain a weaker, shallower cyclone, it is more likely to follow the
low-level westerly to southwesterly flow. This advisory favors that
scenario and shows the storm slowly drifting generally westward to
southwestward through day 4. By day 5, global models are suggesting
a trough to the north will lift Philippe or its remnants
northwestward. A complicating factor to this track forecast is the
proximity of an area of disturbed weather to the east of the
cyclone. Some models are still showing a binary interaction between
the two systems, which will largely depend on the strength of each.
Significant changes have been made to the most recent track
forecast, that are largely related to a slower westward progression
of Philippe. Still, this forecast is a blend of the previous
advisory and the latest model guidance. Further adjustments may be
required in subsequent advisories.

Philippe is in an environment with moderate southwesterly vertical
wind shear and lower, upshear, mid-level relative humidities. These
conditions are likely to inhibit intensification in the near-term
time frame. In about 48 h, global models predict the vertical wind
shear to increase and likely cause Philippe to gradually weaken
through the forecast period. However, there remains
higher-than-average uncertainty in the intensity forecast. The
latest NHC forecast still calls for Philippe to become a remnant low
by day 4.


FORECAST POSITIONS AND MAX WINDS

INIT 28/0900Z 18.8N 54.6W 45 KT 50 MPH
12H 28/1800Z 19.1N 55.4W 45 KT 50 MPH
24H 29/0600Z 19.3N 56.0W 45 KT 50 MPH
36H 29/1800Z 19.2N 56.5W 40 KT 45 MPH
48H 30/0600Z 18.9N 57.1W 40 KT 45 MPH
60H 30/1800Z 18.5N 57.6W 35 KT 40 MPH
72H 01/0600Z 18.0N 58.3W 35 KT 40 MPH
96H 02/0600Z 18.2N 59.3W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 03/0600Z 19.0N 60.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Bucci