Official Discussion issued by the National Hurricane Center

Philippe (AL172023) DATA RELEASED: 9/28/2023 3:00:00 AM UTC

Copy of official data

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.


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