Tropical Cyclone Discussion
830 WTPZ42 KNHC 210247 TCDEP2 Tropical Storm Polo Discussion Number 2 NWS National Hurricane Center Miami FL EP172026 900 PM CST Sun Sep 20 2026 After a brief hiccup in the convective structure on satellite imagery this evening, several convective bursts have formed close to the estimated center of circulation. Earlier microwave images showed a decent low-level structure, though there was some eastward tilt with height. The 00 UTC Dvorak intensity estimate from TAFB was up to T3.0/45 kt, but the objective intensity estimates from UW-CIMSS were lower in the 29-39 kt range. Still, these values are enough support to increase the winds to 35 kt, making the depression Tropical Storm Polo. It remains tricky to find the center this evening, but my best guess is that the center is close to the ongoing convective burst and is estimated to be moving east-northeastward or 075 degrees at 4 kt. Over the next 24-36 h, Polo will likely be influenced by the steering of low- to mid-level ridging south of the cyclone, with most of the track guidance showing a slow eastward or east-southeastward motion on Monday. On Tuesday, mid-level ridging over Texas and Mexico is forecast to build in, and the track guidance responds to this change by showing a sharp, hairpin turn to the northwest that continues through the remainder of the forecast period. The NHC track forecast is close to the prior one, though shows a bit of a sharper turn in 48-60 h, and is a little to the south and west thereafter. This track forecast roughly splits the difference between the reliable HFIP Corrected Consensus Approach (HCCA) and Google DeepMind ensemble mean (GDMI) aids. It is worth noting some of the hurricane-regional models are further east, and short-term trends will be monitored in the guidance over the next day or so to see if any eastward adjustments are needed. Towards the end of the forecast, it is possible Polo may get close enough to the circulation of Odalys to interact, and there is significant track uncertainty in 5 days. Intensity-wise there appear to be few impediments in Polo's forecast, with low shear under 10 kt, very warm 31 C sea-surface temperatures, and abundant deep-layer moisture. While it may take another 12 h or so for Polo to develop an inner core, its possible the ongoing convective burst near the center is already initiating that process. The intensity guidance is rather aggressive, with all of the hurricane-regional models showing various degrees of rapid intensification over the next 2-3 days in addition to the HCCA and GDMI guidance. Thus, the NHC intensity forecast will also show rapid intensification in the 24-60 h period, and now shows Polo becoming a Category 4 hurricane in 72 h. Remarkably, this is still under the latest HCCA and GDMI intensity in that time frame and its possible future upward intensity adjustments will be needed. Thereafter, inner-core fluctuations will likely govern the intensity of Polo in the 3-5 day time frame, but Polo is still likely to be a major hurricane through the end of the forecast period. Key Messages: 1. Heavy rainfall associated with Tropical Storm Polo will impact coastal portions of southwest Mexico this week. This rainfall may produce life-threatening flooding and mudslides, especially in areas of steep terrain. 2. Tropical Storm Polo is forecast to strengthen and move closer to the southwestern Mexican coast as a major hurricane later this week. Although it is too soon to determine the exact location or magnitude of impacts associated with the system, interests in Mexico should closely monitor its progress and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 15.1N 104.6W 35 KT 40 MPH 12H 21/1200Z 15.4N 103.8W 45 KT 50 MPH 24H 22/0000Z 15.4N 103.1W 60 KT 70 MPH 36H 22/1200Z 15.2N 102.4W 80 KT 90 MPH 48H 23/0000Z 15.5N 102.4W 95 KT 110 MPH 60H 23/1200Z 16.0N 103.0W 110 KT 125 MPH 72H 24/0000Z 16.7N 103.7W 115 KT 130 MPH 96H 25/0000Z 18.2N 106.0W 115 KT 130 MPH 120H 26/0000Z 19.5N 109.5W 115 KT 130 MPH