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| #1197410 (Received by flhurricane at: 11:00 AM 09.Sep.2024) TCDAT1 Tropical Storm Francine Discussion Number 4 NWS National Hurricane Center Miami FL AL062024 1000 AM CDT Mon Sep 09 2024 The structure of the system on satellite imagery has improved this morning, with a large circular region of cold convection between -70 to -85 near the estimated center. An Air-Force Reconnaissance Aircraft is sampling the system this morning and earlier found a cyclonic wind shift from southeasterly to northwesterly flow near the center of the mass of deep convection. This data provides enough evidence that a well-defined circulation now exists, and thus PTC Six has become Tropical Storm Francine with sustained winds of 45 kt this advisory. The estimated motion is still tricky given the center only recently formed but is estimated still off to the north-northwest at 340/4 kt. The system is expected to gradually turn northward and then north-northeastward as it moves between a mid-level ridge centered over Cuba and a broad mid- to upper-level trough located to its northwest over Texas. The guidance this cycle has shifted a little eastward and faster, and the NHC track forecast was once again nudged in that direction. The current track splits the difference between HCCA and TVCN and still shows Francine moving ashore of Louisiana sometime on Wednesday evening. There remains a decent amount of track uncertainty with the GEFS and EPS ensembles showing along-track spread implying some speed differences near landfall. While the system is now a tropical storm, the inner core wind field per reconnaissance observations is still broad and in the organizing stage, and initial intensification will be gradual. However, after an inner-core becomes established, and assuming the cyclone`s vertical structure becomes aligned, a period of more significant intensification is possible while storm is embedded in a low shear, high mid-level moisture, and over very warm 30-31 C sea-surface temperatures. The SHIPS rapid intensification (RI) indices are pretty elevated, and a period of RI could also occur between 24-48 h. For now, the NHC intensity forecast will not explicitly forecast RI, but is higher than the previous cycle and shows a 75 kt peak in 48 h, in good agreement with the intensity consensus aids. After that period, southwesterly vertical wind shear quickly increases from 10 kt to more than 30 kt and the intensity could plateau as it approaches the northwestern U.S. Gulf coastline, though the system is forecast to remain a hurricane at landfall. The NHC intensity forecast continues to be in good agreement with the consensus aids, but is a bit under the HAFS-A/B and COAMPS-TC models. Given the latest forecast, a Hurricane Watch has been issued for the Louisiana coastline from Cameron to Grand Isle, and a Storm Surge Watch has been issued from High Island, TX eastward to the Mississippi/Alabama Border. With this advisory, the experimental cone graphic that includes inland Hurricane and Tropical Storm watches in the U.S. will be available on the NHC website. Due to the time needed to compile the inland watch information, the experimental cone graphic will not be available as quickly as the operational cone. The experimental cone graphic can be found from a link on the page with the operational cone graphic once it is available on hurricanes.gov. KEY MESSAGES: 1. Francine is forecast to be a hurricane when it reaches the northwestern Gulf coast on Wednesday or Wednesday night and there is an increasing likelihood of life-threatening storm surge inundation for portions of the Upper Texas and Louisiana coastlines where a Storm Surge Watch is in effect. Residents in the watch area should follow advice given by local officials. 2. There is an increasing risk of damaging hurricane-force winds in portions of southern Louisiana beginning Wednesday, where a Hurricane Watch is now in effect. 3. Francine is expected to bring heavy rainfall and the risk of considerable flash flooding along the coast of far northeast Mexico, portions of the southernmost Texas coast, the Upper Texas Coast, southern Louisiana, and southern Mississippi into Thursday morning. A risk of flash and urban flooding exists across portions of the Mid-South from Wednesday into Friday morning. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 23.0N 94.9W 45 KT 50 MPH 12H 10/0000Z 24.0N 95.4W 50 KT 60 MPH 24H 10/1200Z 24.9N 95.7W 55 KT 65 MPH 36H 11/0000Z 26.3N 95.0W 65 KT 75 MPH 48H 11/1200Z 28.0N 93.5W 75 KT 85 MPH 60H 12/0000Z 29.7N 92.2W 75 KT 85 MPH...ON THE COAST 72H 12/1200Z 32.4N 90.7W 35 KT 40 MPH...INLAND 96H 13/1200Z 36.2N 89.6W 25 KT 30 MPH...POST-TROPICAL 120H 14/1200Z 37.5N 88.8W 20 KT 25 MPH...POST-TROPICAL $$ Forecaster Papin |
