ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Tropical Storm John Discussion Number 17 NWS National Hurricane Center Miami FL EP102024 900 PM CST Thu Sep 26 2024 The convection near the center of John has weakened significantly over the past 12 hours. A curved band off to the southwest and west of John's center is producing a continuous large area of deep convection. Subjective Dvorak current intensity estimates from TAFB and SAB range from 65 to 77 kt, but the objective intensity estimates from UW-CIMSS range from 49 to 56 kt. Since the convection over the center has warmed on infrared imagery and appears to be less organized over the past 12 hours, the initial intensity is being lowered to 60 kt for this advisory. John has been moving northwestward, or 315/4 kt, which is a bit faster than before. This slow motion is forecast to continue for another 12 to 24 h, as John moves near the coastline or just inland late tonight and early tomorrow. After that, a turn to the west-northwest with some acceleration is forecast, if John survives its interaction with the higher topography in this part of Mexico. The latest track forecast is a little to the left and slightly faster than the previous forecast, and is very near the lastest HCCA corrected consensus aid. It seems unlikely that John will be able to restrengthen since the center is now just 20 miles from the coastline and is forecast to move even closer to the coast over the next several hours. Since John's core has been disrupted by the topography today, it is unlikely to recover, despite relatively favorable environmental conditions. Little change in strength, or perhaps slow weakening, is likely over the next 12 hours until the center reaches the coastline. Thereafter, faster weakening is expected on Friday as the center moves near or along the coastline. The latest NHC intensity forecast is near the middle of the intensity guidance suite. It is quite possible that John could weaken to a remnant low and dissipate sooner than forecast. KEY MESSAGES: 1. Tropical Storm John will bring additional very heavy rainfall to coastal portions of southwest Mexico through Friday. The additional rainfall totals will be falling across areas that have received very heavy rainfall amounts over the past few days. This heavy rainfall will likely cause significant and catastrophic life-threatening flash flooding and mudslides to the Mexican States of Guerrero and Michoacán. 2. John is forecast to continue bringing tropical storm conditions across portions of the Tropical Storm Warnings area through Friday. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 17.9N 103.2W 60 KT 70 MPH 12H 27/1200Z 18.3N 103.4W 55 KT 65 MPH...INLAND 24H 28/0000Z 19.0N 104.4W 35 KT 40 MPH...OVER WATER 36H 28/1200Z 19.5N 105.7W 25 KT 30 MPH 48H 29/0000Z 20.2N 107.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 29/1200Z 20.8N 108.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 30/0000Z...DISSIPATED $$ Forecaster Hagen NNNN
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Page last modified: Tuesday, 31-Dec-2024 12:10:17 UTC