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There is currently nothing on the horizon tropically in the Atlantic before Hurricane Season starts on June 1st.
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| #1157930 (Received by flhurricane at: 11:02 PM 18.Oct.2023) TCDAT5 Tropical Storm Tammy Discussion Number 2 NWS National Hurricane Center Miami FL AL202023 1100 PM AST Wed Oct 18 2023 Tammy`s center remains difficult to pinpoint this evening. While a persistent area of deep convection continues to be present near and to the south of the estimated center, an SSMIS microwave pass that came in after the prior advisory suggested the tropical storm still has poor structural organization with some vertical tilt. It is possible the center remains somewhat elongated or it could be attempting to redevelop further into the deep convection. The initial intensity will remain 35 kt for this advisory, in best agreement with the TAFB subjective intensity estimate at 00 UTC. Data from NOAA-P3 and Air Force reconnaissance missions, set to take off tomorrow, will be helpful to better diagnose Tammy`s structure. The motion continues to be more uncertain than usual given the current structure. The tropical storm still appears to be moving westward, but is starting to slow down at 270/15 kt. A well-established mid-level ridge is steering Tammy westward currently, but it is expected to gradually erode as a sharp mid-latitude trough swings off the Eastern U.S. seaboard in the next couple of days. The net result of this pattern change is that Tammy is forecast to slow down and begin turning gradually poleward toward the west-northwest and northwest in the next 2-3 days. Beyond that time, Tammy is forecast to move northward and may begin to recurve into the open Atlantic by the end of the forecast. As mentioned previously, the guidance generally agrees on this scenario, but there are significant track details related to the model-depicted vertical depth of Tammy and how sharp of a turn northward the storm makes. There are also along-track differences too, with the ECMWF much faster than the latest GFS forecast. Compared to the previous cycle, the guidance has shifted eastward and is a bit slower too, and the NHC track was shifted in that direction, roughly in between the consensus aids HCCA and TVCN. The intensity forecast is somewhat tricky. SHIPS diagnosed shear from the GFS and ECMWF is currently light to moderate, between 10-20 kt out of the northwest. The GFS-based SHIPS suggests this shear could even lower some over the next 24-48 h. The lower shear, combined with very warm 29-30 C sea-surface temperatures could potentially promote significant intensification. However, the potential for any intensification is dependent on the storm structure, which remains more uncertain than usual given the lack of recent high resolution microwave or scatterometer data. To add to the uncertainty, the most recent HAFS-A/B runs show little to no intensification, and in fact appear to lose the vortex in their inner-nest beyond 24 hours. The NHC intensity forecast continues to show intensification to around 55 kt over the next 36 h, but only more gradual intensification thereafter, assuming that moderate vertical wind shear will keep the storm in check. This forecast is near or just above the consensus aids. However, this could end up on the conservative side if Tammy is able to become more vertically aligned in the short-term, as suggested by the latest GFS and HWRF forecasts. KEY MESSAGES: 1. Tropical storm conditions are possible across portions of the Lesser Antilles beginning on Friday. Tropical storm watches are currently in effect for Barbados, Dominica, Martinique, and Guadeloupe, and additional watches or warnings will likely be required on Thursday. 2. Heavy rains from Tammy will begin to affect the northern Windward and Leeward 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 19/0300Z 13.0N 53.1W 35 KT 40 MPH 12H 19/1200Z 13.2N 55.0W 40 KT 45 MPH 24H 20/0000Z 13.7N 56.8W 50 KT 60 MPH 36H 20/1200Z 14.3N 58.6W 55 KT 65 MPH 48H 21/0000Z 15.4N 60.3W 55 KT 65 MPH 60H 21/1200Z 16.8N 61.6W 60 KT 70 MPH 72H 22/0000Z 18.4N 62.5W 60 KT 70 MPH 96H 23/0000Z 22.0N 63.4W 70 KT 80 MPH 120H 24/0000Z 27.5N 60.0W 70 KT 80 MPH $$ Forecaster Papin |
