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| #1148728 (Received by flhurricane at: 10:56 AM 21.Aug.2023) TCDAT3 Tropical Storm Franklin Discussion Number 4 NWS National Hurricane Center Miami FL AL082023 1100 AM EDT Mon Aug 21 2023 There are no lack of cold cloud tops associated with Tropical Storm Franklin this morning. The structure on satellite consists of a large bursting pattern, with cloud tops as cold as -90C close to and just east of the estimated center. However, it is unclear if any of this deep convection has resulted in structural improvement to the storm, with the most recent microwave imagery from a SSMIS F-16 pass at 1007 UTC showing a chaotic structure, with evidence the center remains near the western edge of this large convective shield. The latest subjective satellite intensity estimates form TAFB is unchanged from earlier this morning. Thus, the initial intensity will remain 45 kt this advisory, which is also close to the latest D-MINT and D-PRINT estimates from UW-CIMSS. Franklin does appear to be slowing down a tad this morning while moving westward, with the latest estimate at 270/5 kt. The track forecast in the short-term is a bit problematic, with a large spread in model solutions even at 12 h, much higher than the climatological spread. This initial uncertainty may be related intensity differences in the global models, with some of the stronger guidance suggesting the tropical cyclone might reform further to the north and east over the next 12-24 hours. Thereafter, a large weakness to the north of Franklin, produced by a large mid-ocean trough draped across the Western Atlantic, should allow the storm to begin moving northward. A mid-latitude trough reinforces this weakness to the north in 60-72h, allowing the storm to begin moving northeastward. The most significant change in the guidance this cycle is the majority are quite a bit slower than the prior cycle, and the NHC forecast track was slowed down a bit, but not as much as some of the consensus aids. Currently, Franklin is experiencing some moderate 15-20 kt westerly shear, which has paused its intensification for the time being. However, this shear is forecast to gradual decrease as it begins to move more northward, providing an opportunity for the tropical storm to strengthen as it approaches Hispaniola. Some weakening appears likely once the system moves over Hispaniola, especially if the storm moves over the highest terrain in the Dominican Republic. By Thursday, Franklin should be back over open waters in the Atlantic Ocean and has an opportunity to start strengthening again. However, the environment does not appear to be especially pristine, with the ECMWF showing more southwesterly vertical wind shear than the GFS. For now, its assumed this shear will not prevent slow intensification, possibly because the storm should be moving in the same direction as the shear vector, and the NHC intensity forecast will still show Franklin becoming a hurricane towards the end of the forecast period. This forecast is in best agreement with the HFIP corrected consensus approach (HCCA) but remains lower than some of the more aggressive regional-hurricane models (COAMPS-TC, HWRF). KEY MESSAGES: 1. Heavy rainfall from Franklin is expected across portions of Puerto Rico and Hispaniola through the middle of the week. The heavy rainfall may produce areas of flash and urban flooding as well as river rises and mudslides. Across Hispaniola, significant and potentially life-threatening flash flooding is possible Tuesday into Wednesday. 2. Franklin is expected to bring tropical storm conditions to portions of the Dominican Republic and Haiti beginning on Tuesday where Tropical Storm Warnings are in effect. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 15.0N 70.1W 45 KT 50 MPH 12H 22/0000Z 15.2N 70.5W 45 KT 50 MPH 24H 22/1200Z 15.7N 71.0W 50 KT 60 MPH 36H 23/0000Z 17.3N 70.9W 55 KT 65 MPH 48H 23/1200Z 19.2N 70.6W 45 KT 50 MPH...INLAND 60H 24/0000Z 21.2N 69.9W 45 KT 50 MPH...OVER WATER 72H 24/1200Z 22.8N 68.4W 55 KT 65 MPH 96H 25/1200Z 24.4N 65.2W 65 KT 75 MPH 120H 26/1200Z 26.4N 63.7W 75 KT 85 MPH $$ Forecaster Papin |
