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WTNT42 KNHC 280235

TCDAT2

 

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