####018003839####
WTNT42 KNHC 250243

TCDAT2

 

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