ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Tropical Storm John Discussion Number 3 NWS National Hurricane Center Miami FL EP102024 300 AM CST Mon Sep 23 2024 Satellite images indicate that John continues to become better organized, with very deep convection near the center and some tight curved band features. Earlier microwave imagery also showed some inner core development, with perhaps a partial eyewall trying to form. Subjective Dvorak estimates at 06z were 35 kt from both TAFB/SAB, though the objective values were between 40-50 kt. The intensity is set to 40 kt as a blend of these data. The storm is moving slowly to the north-northeast, caught in the large-scale southwesterly flow associated with the monsoon trough near Central America. There has been a big change in most of the track guidance since yesterday, with a fair number of the models now showing a steadier northeastward motion with less eastward steering from the incipient tropical cyclone in the northwestern Caribbean Sea. Consequently, the models have shifted leftward and faster. The official forecast is also trended in that direction, but could still be too far to the east. John is forecast to be over very warm waters with light shear while it approaches the coast of Mexico over the next day or so. While none of the regional hurricane models make John a hurricane before landfall, the rapid intensification indices are indicating at least a 50 percent chance that this system strengthens 30 kt in the next 24 hours, which would indicate hurricane-strength. Given the uncertainties involved, a Hurricane Watch and a Tropical Storm Warning have been issued by the government of Mexico for portions of the coast of southern Mexico on this advisory, and interests there should closely monitor for future forecast updates. KEY MESSAGES: 1. Slow-moving Tropical Storm 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. 2. John is forecast to strengthen before landfall, and a Hurricane Watch and a Tropical Storm Warning have been issued for a portion of the coastline of southern Mexico, where tropical storm conditions could begin late today. 3. John could strengthen more than forecast depending on how long it remains over water. Interests along the coast of southern Mexico should monitor the latest forecast updates, as Hurricane Warnings could be required for a portion of the coastline later today. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 14.4N 98.5W 40 KT 45 MPH 12H 23/1800Z 14.8N 98.2W 50 KT 60 MPH 24H 24/0600Z 15.4N 97.6W 60 KT 70 MPH 36H 24/1800Z 15.8N 97.2W 60 KT 70 MPH 48H 25/0600Z 16.0N 97.0W 45 KT 50 MPH...INLAND 60H 25/1800Z...DISSIPATED $$ Forecaster Blake NNNN
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Page last modified: Tuesday, 31-Dec-2024 12:10:17 UTC