{"id": "1212617885759340551", "title": "Tropical Cyclone Discussion", "adv_date": "2026-09-23T03:00:00Z", "msg": "970\nWTPZ42 KNHC 230253\nTCDEP2\n \nHurricane Polo Discussion Number  10\nNWS National Hurricane Center Miami FL       EP172026\n900 PM CST Tue Sep 22 2026\n \nThe last few fixes this afternoon from the NOAA P-3 Hurricane Hunter \naircraft suggested that Polo was in the middle of an eyewall \nreplacement cycle (ERC). Flight level winds from the inner eyewall \nhad been decreasing in addition to rising pressures and somewhat \nless pronounced warm core in the center. The secondary eyewall was \nalso seen on polar-orbiter imagery with a much larger eyewall taking \nshape on both the SSMIS and WSFM microwave passes compared to this \nmorning. The satellite structure of Polo also looks less pristine \ndue to the ongoing ERC, with some erosion and expansion of the cold \ncloud tops that surround the eye. Based on the earlier aircraft data \nand evolution of satellite imagery since that time, the initial \nintensity is being set at 145 kt this advisory, still making Polo a \nvery dangerous category 5 hurricane.\n \nOne-minute mesosector imagery over Polo has been very useful to \nmonitor its motion, and the inner eye of the storm has been \nwobbling, with the best guess motion an northeastward drift at 45 \ndegrees at 1 kt. The track guidance remains insistent that Polo will \nsoon undergo a slow but sharp turn to the northwest and \nwest-northwest as a deep-layer ridge centered over east Texas \ncontinues to build in. In fact, the track guidance this cycle shows \neven more of a leftward bend in 48-72 h as the ridge moves westward \nwith the hurricane. While the latest NHC track forecast is very \nclose to the prior one for the first 36 h, it is a little slower \ngiven the current motion, and then further south and west beyond 36 \nh. This track will still take Polo close to, but just offshore of \nthe southwestern Mexican coast, where tropical storm conditions are \nstill expected. The latest NHC forecast lies closest to the Google \nDeepMind ensemble mean (GDMI). Toward the end of the forecast \nperiod, the ridge steering Polo is forecast to become eroded by a \ncombination of Tropical Storm Odalys located to its west, and a \ndigging mid-latitude trough moving into the western United States \ncoast. Thus, Polo will likely turn back northwestward or even \nnorthward by the end of the forecast period, though this has also \nbeen shifted west of the prior track following the leftward shift in \nthe guidance this cycle. There still remains significant uncertainty \nin Polo's track in the 4-5 day period.\n \nEnvironmental conditions remain very favorable over Polo currently.\nVertical wind shear is forecast to remain below 10 kt for the next\n24 h, with plenty of nearby deep-layer moisture. In addition, Polo\nis over the warmest sea-surface temperatures in the basin, which\nalso extend vertically well below the surface, which should limit\nocean upwelling of the slow moving hurricane. However, the big\nquestion mark is how the ongoing ERC will evolve in the next    \n12-24 h. The last few microwave images already show a larger closed\neyewall taking shape. There are also hints of the ERC successfully\ncompleting in the next 24 h in the most recent raw output from the\n18z HAFS-A run. Thus, the NHC intensity forecast shows some\nshort-term fluctuations in intensity both down and up over the next\n24-36 h, though it is difficult to forecast these inner-core\nstructural changes with much confidence. SHIPS guidance thereafter\ncontinues to indicate an increase in easterly shear as the ridging\noverhead intensifies, and the NHC intensity forecast shows gradual\nweakening beginning by that time, with a somewhat faster rate of\nweakening now shown in days 4-5. However, this intensity forecast\nremains on the high side of the guidance except for the HFIP\nCorrected Consensus Approach (HCCA), which is a good 20-30 kt\nhigher than the rest of the guidance this cycle.\n \n \nKey Messages:\n \n1. Heavy rainfall associated with Polo will impact coastal portions\nof southwest Mexico through Thursday. This rainfall may produce\nlife-threatening flooding and mudslides, especially in areas of\nsteep terrain.\n \n2. A Tropical Storm Warning is in effect for portions of\nsouthwestern Mexico, and the Tropical Storm Watch is in effect\nwestward to Playa Perula. Interests in these areas should closely\nmonitor updates to the forecast.\n \n \nFORECAST POSITIONS AND MAX WINDS\n \nINIT  23/0300Z 14.7N 101.3W  145 KT 165 MPH\n 12H  23/1200Z 15.0N 101.6W  140 KT 160 MPH\n 24H  24/0000Z 15.9N 102.8W  145 KT 165 MPH\n 36H  24/1200Z 16.4N 104.3W  140 KT 160 MPH\n 48H  25/0000Z 16.6N 106.1W  135 KT 155 MPH\n 60H  25/1200Z 16.8N 108.0W  125 KT 145 MPH\n 72H  26/0000Z 17.0N 110.0W  120 KT 140 MPH\n 96H  27/0000Z 18.2N 112.7W  110 KT 125 MPH\n120H  28/0000Z 20.9N 113.7W   95 KT 110 MPH\n \n"}