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WTNT42 KNHC 040849

TCDAT2

 

Tropical Storm Philippe Discussion Number  44

NWS National Hurricane Center Miami FL       AL172023

500 AM AST Wed Oct 04 2023

 

Philippe remains a disorganized tropical storm this morning, yet 

continues to produce heavy rainfall over the British and U.S. Virgin 

Islands. This activity remains displaced well to the southeast of 

the estimated circulation center, and appears to be more associated 

with the storm's inflow interacting with a well-defined mid-level 

circulation just north of St. Thomas, which is evident from radar in 

Puerto Rico. Scatterometer data received just after the last 

advisory showed values around 40 kt in this area of convection, and 

the initial intensity will be held at 40 kt. This value is on the 

higher end of the Dvorak intensity estimates, but does match the 

most recent UW-CIMSS SATCON intensity estimate.

 

The earlier scatterometer data suggested that Philippe had slowed 

down some, possibly due to the ongoing convection to its southeast, 

but its latest motion appears to have resumed a more northwestward 

motion at 325/8 kt. The track guidance remains in agreement about 

the storm turning more northward later today, with gradual 

acceleration as the mid-level ridge that has been impeding its 

poleward progress gradually shifts eastward, and Philippe becomes 

steered between a deep-layer low to its west, and the aforementioned 

ridge to its east. Compared to the previous cycle, the guidance has 

shifted a bit eastward over the first 2-3 days of the forecast 

period, and the latest NHC track forecast was shifted a bit further 

east early on, but not as far as the consensus aids. After Philippe 

passes by Bermuda on Friday, it is forecast to interact with a much 

more amplified trough swinging into the northeastern United States 

this weekend. This evolution may result in Philippe's track 

potentially bending back north-northwest on Saturday, approaching 

Atlantic Canada and New England as it phases with the larger trough. 

There still remains quite a bit of spread in the track guidance by 

96 h due to this interaction.  



The intensity forecast remains murky. Right now, the low-level 

circulation of Philippe remains diffuse, and even though vertical 

wind shear could potentially slacken some over the next 24 hours, 

the cyclone appears to be in no state to intensify in the 

short-term. Thereafter, Philippe may have an opportunity to take 

advantage of some synoptic mid-latitude dynamics associated with the 

initial upper-level trough positioned to the west of its 

circulation. Thus, some gradual intensification is shown between 

36-60 h. With that said, some of the model guidance (like the most 

recent GFS run) shows Philippe instead being absorbed into this 

non-tropical feature, though that solution is not shown at this 

time. Regardless, increasing baroclinicity should also begin to 

initiate extratropical transition after 48 hours, which is forecast 

to be fully complete sometime in the 72-96 h forecast time frame. 

The latest NHC intensity forecast remains near the middle of the 

guidance envelope, and is also close to the HFIP Corrected 

Consensus Approach (HCCA). 

 

KEY MESSAGES:

 

1. Heavy rainfall from Philippe is expected to produce scattered

flash flooding across portions of the United States & British Virgin

Islands through today.

 

2. Gusty winds are likely to continue across portions of the

northern Leeward Islands and the Virgin Islands through early today.

 

3. The risk is increasing for tropical storm conditions to occur on

Bermuda late this week.  Interests on Bermuda should monitor the

progress of Philippe, and Tropical Storm Watches could become 

required for the island later today. 

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  04/0900Z 20.5N  65.5W   40 KT  45 MPH

 12H  04/1800Z 21.4N  65.8W   40 KT  45 MPH

 24H  05/0600Z 23.3N  66.0W   40 KT  45 MPH

 36H  05/1800Z 26.0N  66.0W   45 KT  50 MPH

 48H  06/0600Z 29.0N  65.5W   45 KT  50 MPH

 60H  06/1800Z 32.0N  65.0W   50 KT  60 MPH

 72H  07/0600Z 35.3N  65.1W   50 KT  60 MPH

 96H  08/0600Z 43.1N  66.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

120H  09/0600Z 51.5N  72.0W   30 KT  35 MPH...POST-TROP/EXTRATROP

 

$$

Forecaster Papin