####018002681#### WTNT45 KNHC 240848 TCDAT5 Hurricane Tammy Discussion Number 24 NWS National Hurricane Center Miami FL AL202023 500 AM AST Tue Oct 24 2023 Tammy's satellite depiction has improved slightly compared to the sheared convective pattern from yesterday evening. The latest infrared satellite imagery depicts convective bursts are once again wrapping around the southern portion of the system. Earlier microwave imagery showed a well organized low-to mid-level circulation. The most recent TAFB Dvorak satellite estimate held steady at T4.0/65kt, which supports maintaining an initial intensity of 65 kt for this advisory. The hurricane is currently moving northeastward, and should continue this motion for the next day or two. A mid-latitude trough approaching the system from the northwest will cause Tammy to begin to move more northward during the middle of the forecast period. It is after this point, the model guidance becomes increasingly divergent. Models are split on whether another mid-latitude trough will cause the system to accelerate east to northeastward, or have Tammy not being picked up by this trough and move the system westward to southwestward under a building mid-level ridge. The GFS has trended towards the west-southwest track scenario, closer to the ECMWF. Therefore, the NHC forecast track, which already favored the ECMWF solution, remains similar to the previous advisory and is close to a blend of GFS and ECMWF. There is considerably better agreement among most of the intensity guidance, which indicates slight strengthening is possible during the next day or two, as Tammy interacts with an upper-level trough. After 48 hours the system should begin to weaken and start to transition into a post-tropical cyclone. The latest model simulated satellite imagery depicts that this process is expected to be complete in about 60 h, though Tammy will likely continue to produce gale-to storm-force winds for several days even after this transition occurs. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 23.7N 62.8W 65 KT 75 MPH 12H 24/1800Z 24.5N 61.8W 70 KT 80 MPH 24H 25/0600Z 25.9N 60.3W 75 KT 85 MPH 36H 25/1800Z 27.9N 59.0W 75 KT 85 MPH 48H 26/0600Z 29.5N 58.9W 70 KT 80 MPH 60H 26/1800Z 31.0N 59.7W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 27/0600Z 31.7N 60.9W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 28/0600Z 32.4N 62.8W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 29/0600Z 32.8N 64.8W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Kelly ####018003678#### WTPZ43 KNHC 240848 TCDEP3 Tropical Storm Otis Discussion Number 8 NWS National Hurricane Center Miami FL EP182023 400 AM CDT Tue Oct 24 2023 Otis has strengthened overnight. There has been a significant increase in banding and the center is now well embedded within the deep convection. While there has been no recent microwave imagery to evaluate the inner core structure, a couple of earlier ASCAT overpass indicated that the center had become embedded within the cold cloud tops. The initial intensity has been increased to 55 kt for this advisory, and that is in agreement with subjective Dvorak data T-numbers of 3.5 from both SAB and TAFB. It appears that the vertical shear over Otis has decreased as there has been an expansion of the cirrus outflow over the eastern portion of the storm. The shear is expected to remain light to moderate while Otis moves over SSTs of 29-30 degrees C during the next day or so. These conditions should allow for continued strengthening as Otis approaches the southern coast of Mexico. The latest NHC intensity forecast calls for Otis to become a hurricane today, and it shows additional strengthening before Otis reaches southern Mexico in a day or so. By 36 hours, Otis is forecast to be inland, and rapid weakening should occur as the cyclone moves over mountainous terrain. The NHC intensity forecast is at the high end of the guidance in best agreement with the HWRF and HAFS-B models. The SHIPS Rapid Intensification Index now shows about a 1 in 4 chance of rapid strengthening during the next 24 hours, which supports being on the higher side of the guidance. Otis is moving north-northwestward at about 7 kt. A north-northwest motion is expected to continue during the next couple of days between a mid- to upper-level trough to the cyclone's northwest and a ridge to its east. The GFS has finally come onboard with this scenario and the track guidance is much more tightly clustered than before. The main difference is in the forward speed with the ECMWF being on the faster side of the guidance envelope. The NHC forecast is near a blend of the latest GFS and ECMWF models, which is a little faster than the simple consensus aids. Based on the updated track and intensity forecast, the government of Mexico has issued a Hurricane Warning for a portion of the southern coast of Mexico. Key Messages: 1. Otis is forecast to become a hurricane before it reaches the southern coast of Mexico late tonight or Wednesday, and hurricane and tropical storm conditions are expected along portions of the southern coast of Mexico where hurricane and tropical storm warnings are in effect. 2. Heavy rains from Otis will begin to impact areas of southern and southwestern Mexico later today. This rainfall will produce flash and urban flooding, along with mudslides in areas of higher terrain. 3. A dangerous storm surge is expected to produce significant coastal flooding near and to the east of where the center makes landfall. Near the coast, the surge will be accompanied by large and destructive waves. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 14.2N 98.5W 55 KT 65 MPH 12H 24/1800Z 15.0N 99.0W 65 KT 75 MPH 24H 25/0600Z 16.1N 99.7W 75 KT 85 MPH 36H 25/1800Z 17.1N 100.3W 70 KT 80 MPH...INLAND 48H 26/0600Z 17.9N 100.9W 35 KT 40 MPH...INLAND 60H 26/1800Z 18.6N 101.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 27/0600Z...DISSIPATED $$ Forecaster Brown