{"id": "1212121534291181575", "title": "Tropical Cyclone Discussion", "adv_date": "2026-09-21T09:00:00Z", "msg": "624\nWTPZ42 KNHC 210848\nTCDEP2\n \nTropical Storm Polo Discussion Number   3\nNWS National Hurricane Center Miami FL       EP172026\n300 AM CST Mon Sep 21 2026\n \nDeep convection associated with Polo has been gradually increasing \nover the past several hours. A recent GMI microwave pass indicates \nthat Polo is developing a small core, which is an early indication \nthat significant strengthening could be beginning. The latest \nsatellite intensity estimates range from 35 to 45 kt, and based on \nthat data and an earlier ASCAT pass, the initial intensity is \nincreased to 40 kt.\n\nEnvironmental conditions appear very conducive for strengthening \nwith the vertical wind shear expected to be less than 10 kt, \nmid-level humidities near or above 70 percent, and SSTs above 30 C \nduring the next several days. These conditions, along with Polo's \nimproving and compact structure, support rapid intensification. In \nfact, the SHIPS Rapid Intensification indices indicates that there \nis a near 90 percent chance of an increase in winds of at least 55 \nkt over the next 48 hours. The NHC intensity forecast is quite \naggressive and calls for rapid intensification, and shows Polo \nbecoming a hurricane later today and a major hurricane on Tuesday. \nThis prediction is higher than the previous one, but below the \nlatest HCCA guidance which shows Polo reaching category 5 status in \nabout 48 hours. \n \nThe storm will likely drift eastward or southeastward during the \nnext day or so in weak steering currents. However, a sharp turn to \nthe west-northwest or northwest is expected by late Tuesday when a \nmid-level ridge becomes established to the northeast of Polo. This \npattern should bring the core of the storm near the coast of \nsouthwestern Mexico on Wednesday and Thursday, and then well south \nof the Baja California Peninsula on Friday. There is a very large \nspread in the model solutions in where, when, and how sharply Polo \nmakes the turn. The GFS model is on the far south side of the \nguidance envelope while the Google DeepMind ensemble mean is on the \nnorthern edge. The NHC track forecast has been nudged northward, and \nis in best agreement with the corrected consensus HCCA model. It \nshould be noted that given the complex steering pattern and model \nspread, confidence in the details of the track forecast is quite \nlow.\n \nKey Messages:\n\n1. Heavy rainfall associated with Tropical Storm Polo will impact \ncoastal portions of southwest Mexico this week. This rainfall may \nproduce life-threatening flooding and mudslides, especially in areas \nof steep terrain.\n \n2. Polo is forecast to strengthen to a major hurricane while it \nmoves closer to the coast of southwestern Mexico during the next few \ndays. Although the core of the hurricane is forecast to stay \noffshore, it is too soon to determine the exact location or \nmagnitude of impacts. Residents in southwestern Mexico should \nclosely monitor its progress and updates to the forecast. A Tropical \nStorm Watch has been issued for portions of southwestern Mexico.\n \n \nFORECAST POSITIONS AND MAX WINDS\n \nINIT  21/0900Z 15.5N 103.8W   40 KT  45 MPH\n 12H  21/1800Z 15.5N 103.1W   60 KT  70 MPH\n 24H  22/0600Z 15.3N 102.5W   80 KT  90 MPH\n 36H  22/1800Z 15.3N 102.0W  100 KT 115 MPH\n 48H  23/0600Z 15.9N 102.4W  115 KT 130 MPH\n 60H  23/1800Z 16.6N 103.0W  125 KT 145 MPH\n 72H  24/0600Z 17.5N 104.1W  125 KT 145 MPH\n 96H  25/0600Z 18.7N 106.6W  120 KT 140 MPH\n120H  26/0600Z 19.8N 109.0W  115 KT 130 MPH\n \n"}