Tropical Cyclone Discussion
970 WTPZ42 KNHC 230253 TCDEP2 Hurricane Polo Discussion Number 10 NWS National Hurricane Center Miami FL EP172026 900 PM CST Tue Sep 22 2026 The last few fixes this afternoon from the NOAA P-3 Hurricane Hunter aircraft suggested that Polo was in the middle of an eyewall replacement cycle (ERC). Flight level winds from the inner eyewall had been decreasing in addition to rising pressures and somewhat less pronounced warm core in the center. The secondary eyewall was also seen on polar-orbiter imagery with a much larger eyewall taking shape on both the SSMIS and WSFM microwave passes compared to this morning. The satellite structure of Polo also looks less pristine due to the ongoing ERC, with some erosion and expansion of the cold cloud tops that surround the eye. Based on the earlier aircraft data and evolution of satellite imagery since that time, the initial intensity is being set at 145 kt this advisory, still making Polo a very dangerous category 5 hurricane. One-minute mesosector imagery over Polo has been very useful to monitor its motion, and the inner eye of the storm has been wobbling, with the best guess motion an northeastward drift at 45 degrees at 1 kt. The track guidance remains insistent that Polo will soon undergo a slow but sharp turn to the northwest and west-northwest as a deep-layer ridge centered over east Texas continues to build in. In fact, the track guidance this cycle shows even more of a leftward bend in 48-72 h as the ridge moves westward with the hurricane. While the latest NHC track forecast is very close to the prior one for the first 36 h, it is a little slower given the current motion, and then further south and west beyond 36 h. This track will still take Polo close to, but just offshore of the southwestern Mexican coast, where tropical storm conditions are still expected. The latest NHC forecast lies closest to the Google DeepMind ensemble mean (GDMI). Toward the end of the forecast period, the ridge steering Polo is forecast to become eroded by a combination of Tropical Storm Odalys located to its west, and a digging mid-latitude trough moving into the western United States coast. Thus, Polo will likely turn back northwestward or even northward by the end of the forecast period, though this has also been shifted west of the prior track following the leftward shift in the guidance this cycle. There still remains significant uncertainty in Polo's track in the 4-5 day period. Environmental conditions remain very favorable over Polo currently. Vertical wind shear is forecast to remain below 10 kt for the next 24 h, with plenty of nearby deep-layer moisture. In addition, Polo is over the warmest sea-surface temperatures in the basin, which also extend vertically well below the surface, which should limit ocean upwelling of the slow moving hurricane. However, the big question mark is how the ongoing ERC will evolve in the next 12-24 h. The last few microwave images already show a larger closed eyewall taking shape. There are also hints of the ERC successfully completing in the next 24 h in the most recent raw output from the 18z HAFS-A run. Thus, the NHC intensity forecast shows some short-term fluctuations in intensity both down and up over the next 24-36 h, though it is difficult to forecast these inner-core structural changes with much confidence. SHIPS guidance thereafter continues to indicate an increase in easterly shear as the ridging overhead intensifies, and the NHC intensity forecast shows gradual weakening beginning by that time, with a somewhat faster rate of weakening now shown in days 4-5. However, this intensity forecast remains on the high side of the guidance except for the HFIP Corrected Consensus Approach (HCCA), which is a good 20-30 kt higher than the rest of the guidance this cycle. Key Messages: 1. Heavy rainfall associated with Polo will impact coastal portions of southwest Mexico through Thursday. This rainfall may produce life-threatening flooding and mudslides, especially in areas of steep terrain. 2. A Tropical Storm Warning is in effect for portions of southwestern Mexico, and the Tropical Storm Watch is in effect westward to Playa Perula. Interests in these areas should closely monitor updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 14.7N 101.3W 145 KT 165 MPH 12H 23/1200Z 15.0N 101.6W 140 KT 160 MPH 24H 24/0000Z 15.9N 102.8W 145 KT 165 MPH 36H 24/1200Z 16.4N 104.3W 140 KT 160 MPH 48H 25/0000Z 16.6N 106.1W 135 KT 155 MPH 60H 25/1200Z 16.8N 108.0W 125 KT 145 MPH 72H 26/0000Z 17.0N 110.0W 120 KT 140 MPH 96H 27/0000Z 18.2N 112.7W 110 KT 125 MPH 120H 28/0000Z 20.9N 113.7W 95 KT 110 MPH