ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Tropical Storm John Discussion Number 8 NWS National Hurricane Center Miami FL EP102024 300 AM CST Tue Sep 24 2024 John moved inland at around 0315 UTC as a 105 kt Category 3 Hurricane. Since that time, the the storm has apparently turned more leftward and remains just inland, skirting the southern coast of Mexico. While surface observations have been sparse, my best guess is that the storm recently passed just to the north of Acapulco, where the airport earlier reported tropical-storm-force wind gusts and west winds as the pressure dropped to 998 mb. Assuming the small core has continued to quickly weaken, John is being downgraded to a tropical storm, and the initial intensity is 60 kt this advisory. Following fixes from earlier microwave and more recent geostationary satellite imagery, John now appears to be moving northwestward at 310/7 kt. The track forecast, which has been problematic with John from the start, is just as difficult now. John has continued to deviate westward of the previous forecast track and is now moving roughly parallel to the coast of Mexico. To make matters worse, a decent chunk of the of the global models guidance (ECMWF, UKMET) and hurricane regional models (HWRF, HMON) suggest the circulation could continue turning westward and attempt to re-emerge over the Eastern Pacific. Even the GFS and CMC solutions, which appear to dissipate the surface circulation inland over Mexico, show the mid-level circulation persisting and drifting back offshore, leading to the development of a new low-level circulation. Because it is becoming distinctly possible that John does not move far enough inland to dissipate entirely, and the aforementioned continued leftward trends, the latest NHC track forecast is altered quite a bit form the prior forecast, and now shows the possibility that John, albeit as a tropical depression, moving back offshore as it becomes tangled in the larger monsoonal flow. By 72 h, most of the track guidance shows the system moving back inland. The updated track forecast is roughly in between the HCCA and ECMWF trackers, and is of very low confidence given John's track history. It also remains possible the system could dissipate later today if it moves further inland. Intensity-wise, John should continue to rapidly weaken as long as it remains onshore, and the NHC intensity forecast shows the tropical cyclone weakening to a tropical depression later today. However, the new NHC forecast now maintains the system as a depression and does not show dissipation beyond 24 h given the latest track forecast taking the system along the coast of Mexico and not far enough inland to completely dissipate. Some of the models (notably the ECMWF) attempt to also re-intensify John as it gets far enough back offshore, but given the large changes made on this forecast cycle, the NHC intensity will not show that solution quite yet. Even if John remains inland, larger-scale moist monsoonal southeasterly flow will persist along the southern coast of Mexico, likely contributing to catastrophic rainfall both along the coast and inland over the up-slope portion of the mountainous terrain. This is a very dangerous life-threatening flooding scenario. KEY MESSAGES: 1. Tropical Storm John could still producing tropical storm conditions for the next few hours in the tropical storm warning area. 2. Slow-moving John will bring very heavy rainfall to coastal portions of southwest Mexico through the upcoming week. This heavy rainfall will likely cause significant and possibly catastrophic, life-threatening flash flooding and mudslides to the Mexican States of Chiapas, Oaxaca, and southeast Guerrero, particularly in areas near the coast and along the up-slope portion of areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 17.3N 100.0W 60 KT 70 MPH...INLAND 12H 24/1800Z 17.4N 100.8W 30 KT 35 MPH...INLAND 24H 25/0600Z 17.0N 101.0W 30 KT 35 MPH...OVER WATER 36H 25/1800Z 16.7N 100.9W 30 KT 35 MPH 48H 26/0600Z 16.9N 100.6W 30 KT 35 MPH 60H 26/1800Z 17.4N 100.7W 25 KT 30 MPH...INLAND 72H 27/0600Z 18.1N 101.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 28/0600Z...DISSIPATED $$ Forecaster Papin NNNN
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Page last modified: Tuesday, 31-Dec-2024 12:10:17 UTC