|
Show Selection: |
| #1156015 (Received by flhurricane at: 5:03 AM 05.Oct.2023) TCDAT2 Tropical Storm Philippe Discussion Number 48 NWS National Hurricane Center Miami FL AL172023 500 AM AST Thu Oct 05 2023 Philippe`s low-level structure continues to be quite broad and diffuse this morning. This structure has made finding the center position quite a challenge. An earlier 0513 UTC GMI microwave pass confirmed this broad structure, though it did hint at a tighter mesoscale feature tucked under the convection to the southeast of the broader low-level rotation seen on 1-minute GOES-16 imagery. The initial intensity remains 35 kt this advisory, in agreement with the TAFB subjective Dvorak estimate, in addition to an earlier received saildrone observation that had sustained tropical-storm-force winds well to the southeast of the broad circulation center. Because the center is difficult to pinpoint, the initial motion is also uncertain, estimated due north at 360/12 kt. The storm`s current motion is a result of it being steered between a mid-level ridge positioned to its east, and a mid- to upper-level low positioned to its west. This pattern should persist, leading to Philippe gradually accelerating towards Bermuda over the next 24-36 h. Interestingly, the guidance has quite a bit of spread this cycle in the short-term, likely related to how the current broad and diffuse circulation interacts with the trough to its west, with the HAFS-A/B runs notably pivoting Philippe further west early on than the remainder of the guidance. The NHC track forecast ops to favor the simple consensus aids, though it is worth noting the HFIP Corrected Consensus Approach (HCCA) is farther west due to the influence of these HAFS tracks. I guess it is not all that surprising to see Philippe throw one additional curve ball in the track forecast given the extreme difficulty the track forecast for this system has proven to be over the last couple of weeks. After 48 hours, the guidance actually comes back into better agreement, showing a gradual bend north-northwest and northwest when Philippe, now a post-tropical cyclone, reaches the coast of Atlantic Canada or New England this weekend. The intensity forecast presents its own challenges. Assuming that Philippe remains a distinct entity relative to the developing non-tropical low to its west, the storm could intensify while it interacts with this upper-level trough to its west. However, its unclear if this will prove to be a favorable trough interaction, or if this trough will ultimately just absorb the tropical cyclone without much increase in the winds. Regardless, after Philippe passes north of Bermuda, increasing baroclinicity will hasten its transition to an extratropical cyclone. However, FSU phase-space diagrams suggest the system could undergo a warm-seclusion-type transition, resulting in further deepening even after the system becomes extratropical. The post-tropical cyclone is then expected to weaken once it moves inland over Maine and/or Atlantic Canada. The NHC intensity forecast continues to lie near the middle of the guidance envelope. KEY MESSAGES: 1. Tropical storm conditions are expected on Bermuda beginning tonight, where a Tropical Storm Warning remains in effect. Heavy rainfall will also begin to affect the island later today, which could produce flash-flooding. 2. Philippe is likely to move over portions of Atlantic Canada and eastern New England, likely as a post-tropical cyclone by this weekend. Regardless of Philippe`s intensity or structure, interests in those areas should monitor the storm`s progress and be prepared for the possibility of strong winds and heavy rainfall. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 24.8N 65.9W 35 KT 40 MPH 12H 05/1800Z 26.7N 66.0W 35 KT 40 MPH 24H 06/0600Z 30.0N 66.0W 40 KT 45 MPH 36H 06/1800Z 33.3N 66.0W 45 KT 50 MPH 48H 07/0600Z 36.7N 66.2W 50 KT 60 MPH 60H 07/1800Z 40.2N 66.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 08/0600Z 45.2N 67.8W 45 KT 50 MPH...POST-TROP/INLAND 96H 09/0600Z 50.5N 76.0W 30 KT 35 MPH...POST-TROP/INLAND 120H 10/0600Z...DISSIPATED $$ Forecaster Papin |
