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| #1149452 (Received by flhurricane at: 10:54 PM 25.Aug.2023) TCDAT3 Tropical Storm Franklin Discussion Number 22 NWS National Hurricane Center Miami FL AL082023 1100 PM AST Fri Aug 25 2023 Westerly shear continues to affect Franklin tonight, as evidenced by the sharp edge to its cold cloud tops on infrared satellite images. However, the low-level center that was exposed earlier today appears to have moved under the western edge of the convective canopy. An Air Force Reserve Hurricane Hunter aircraft flew the storm at 700 mb this evening and reported peak flight-level winds of 56 kt, with believable SFMR winds in the 45-55 kt range. These data warrant a slight increase to the initial intensity (50 kt), especially given a recent dropsonde that suggests the surface pressure has fallen to 996 mb tonight. A recent ASCAT-B pass over Franklin further supports this, with peak wind vectors slightly above 45 kt. Note that the initial intensity of Franklin is more uncertain than normal, with there being a large spread between some of the aircraft data and the various objective and subjective satellite estimates. The intense convection closer to the center of Franklin appears to have drawn the surface center more northeastward, and the initial motion is an uncertain 60/7 kt. A high pressure ridge building to the east of Franklin is expected to steer the cyclone more northward and north-northwestward this weekend and into early next week. Then, a deep-layer trough is forecast to move across the northeastern U.S. and eastern Canada by midweek. This should cause Franklin to accelerate northeastward deeper into the mid latitudes through the end of the forecast period. The updated NHC track forecast lies to the east of the previous one during the first 60-72 h of the period, mainly a result of the eastward adjustment to the initial position of Franklin. There are some notable forward speed differences beyond 72 h, with the GFS significantly faster than the rest of the global and regional models. With the NHC forecast remaining near the multi-model consensus aids, no notable changes were made to this portion of the track forecast. The westerly shear that has plagued Franklin for the past couple of days is expected to decrease during the next 24-36 h. So while only modest strengthening is forecast in the near term, more significant strengthening seems likely thereafter as the cyclone moves over very warm SSTs (29-30 deg C) and within a more favorable dynamic environment. The updated forecast shows Franklin becoming a hurricane by 48 h and peaking near major hurricane intensity in 72-96 h, in good agreement with the latest HCCA and IVCN aids. As Franklin accelerates to higher latitudes, cooler waters and increased deep-layer shear will induce weakening and eventually extratropical transition beyond the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 22.4N 66.2W 50 KT 60 MPH 12H 26/1200Z 23.0N 66.0W 55 KT 65 MPH 24H 27/0000Z 23.9N 66.3W 55 KT 65 MPH 36H 27/1200Z 25.3N 67.0W 60 KT 70 MPH 48H 28/0000Z 27.0N 67.9W 70 KT 80 MPH 60H 28/1200Z 28.8N 68.4W 80 KT 90 MPH 72H 29/0000Z 30.5N 68.4W 95 KT 110 MPH 96H 30/0000Z 34.7N 66.5W 95 KT 110 MPH 120H 31/0000Z 40.0N 60.0W 75 KT 85 MPH $$ Forecaster Reinhart |
