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| #1151054 (Received by flhurricane at: 4:50 PM 02.Sep.2023) TCDAT4 Tropical Storm Katia Discussion Number 6 NWS National Hurricane Center Miami FL AL122023 500 PM AST Sat Sep 02 2023 Deep convection continues near and north of the center of Katia, with microwave data showing a tilted vortex due to the southerly shear. Overall, the system is showing more internal structure than this morning, which is confirmed by increasing satellite estimates from many sources which mostly lie between 45-55 kt. The initial wind speed is raised to 50 kt as a blend of this data. Katia has turned northwestward at about 11 kt. The storm should move between a large middle- to upper-level low to the west and a narrow mid-latitude ridge over the eastern Atlantic for the next couple of days. The biggest changes from this morning are that uncertainty is increasing in a few days when Katia, or the remnants, reaches a col point between a mid-latitude ridge building over the central Atlantic and deep trough over the northeastern Atlantic. The guidance suite literally has motions in all cardinal directions after that point, indicating a very low confidence situation, and the GEFS ensemble lows show the proverbial squashed spider pattern. Thus, the new forecast stalls the system before dissipating, but it will require some time to sort out the long-range details. The earlier microwave data was showing a growing distance between the mid-level and low-level centers of the cyclone, suggesting that southerly shear could be winning the battle soon (also indicated by the latest infrared satellite data). A continuation of that shear plus a slow increase in dry air is likely to cause Katia to slowly weaken for the next few days. The global models show no significant deep convection after 36 h, and remnant low status is indicated for 48 h. Little change was made to the previous forecast, similar to the NOAA corrected consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 25.0N 30.5W 50 KT 60 MPH 12H 03/0600Z 25.9N 31.5W 45 KT 50 MPH 24H 03/1800Z 26.8N 32.8W 40 KT 45 MPH 36H 04/0600Z 27.5N 33.9W 35 KT 40 MPH 48H 04/1800Z 28.2N 35.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 05/0600Z 28.5N 35.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 05/1800Z 29.0N 35.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 06/1800Z...DISSIPATED $$ Forecaster Blake |
