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| #1158039 (Received by flhurricane at: 5:08 PM 19.Oct.2023) TCDAT5 Tropical Storm Tammy Discussion Number 6 NWS National Hurricane Center Miami FL AL202023 500 PM AST Thu Oct 19 2023 Tammy has not become any better organized since this morning. The center of the cyclone has become partially exposed to the west and northwest of the main area of deep convection, and there is little evidence of banding except over the southeastern portion of the storm. An Air Force Reserve reconnaissance aircraft has been investigating Tammy this afternoon and has reported peak 850 mb flight-level winds of 53 kt and SFMR values of around 40 kt. Earlier scatterometer data revealed some 40-45 kt vectors over the southeastern portion of the circulation. Based on these data, the initial intensity is held at 50 kt for this advisory. After taking a more westward jog earlier this afternoon, the latest aircraft fixes suggest the west-northwestward motion has resumed. The latest motion estimate is 285 degrees at 11 kt. Tammy is nearing the western periphery of a subtropical ridge over the central Atlantic and the cyclone should turn northwestward within the next day or so. This motion is expected to bring the center of Tammy near or over portions of the Leeward Islands late Friday and Saturday. Once Tammy is north of the Leeward Islands on Sunday, it is expected to turn northward around the western side of the aforementioned ridge. There has been little overall change with the track guidance this cycle. The GFS and ECMWF models remain along the eastern side of the guidance envelope, while the models that show less strengthening are along the far western side of the guidance. The NHC track forecast remains nears the middle of the guidance envelope between the HFIP corrected consensus and the TCVA simple consensus aid. The current structure of Tammy does not suggest that it will strengthen very quickly during the next day or so, but warm SSTs and moderate vertical shear conditions could allow for some modest intensification after that and the NHC official forecast still calls for Tammy to become a hurricane in a couple of days. After that time, some additional strengthening is forecast after Tammy moves north of the Leeward Islands and recurves over the central Atlantic. KEY MESSAGES: 1. Tropical storm conditions are expected to begin in portions of the Lesser Antilles beginning Friday, where a tropical storm warning is in effect. Tropical storm and hurricane conditions are possible elsewhere in the Leeward Islands where hurricane and tropical storm watches are currently in effect. Additional watches and warnings will likely be required tonight. 2. Heavy rains from Tammy will begin to affect the Leeward and northern Windward Islands on Friday, spreading into the British and U.S. Virgin Islands and Puerto Rico over the weekend. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 13.7N 56.6W 50 KT 60 MPH 12H 20/0600Z 14.2N 58.2W 50 KT 60 MPH 24H 20/1800Z 15.0N 59.9W 55 KT 65 MPH 36H 21/0600Z 16.4N 61.4W 60 KT 70 MPH 48H 21/1800Z 17.9N 62.4W 65 KT 75 MPH 60H 22/0600Z 19.5N 63.1W 70 KT 80 MPH 72H 22/1800Z 21.0N 63.3W 75 KT 85 MPH 96H 23/1800Z 24.3N 62.3W 75 KT 85 MPH 120H 24/1800Z 28.5N 57.5W 75 KT 85 MPH $$ Forecaster Brown |
