{"id": "1212050562250276871", "title": "Tropical Cyclone Discussion", "adv_date": "2026-09-21T03:00:00Z", "msg": "830\nWTPZ42 KNHC 210247\nTCDEP2\n \nTropical Storm Polo Discussion Number   2\nNWS National Hurricane Center Miami FL       EP172026\n900 PM CST Sun Sep 20 2026\n \nAfter a brief hiccup in the convective structure on satellite \nimagery this evening, several convective bursts have formed close \nto the estimated center of circulation. Earlier microwave images \nshowed a decent low-level structure, though there was some \neastward tilt with height. The 00 UTC Dvorak intensity estimate \nfrom TAFB was up to T3.0/45 kt, but the objective intensity \nestimates from UW-CIMSS were lower in the 29-39 kt range. Still, \nthese values are enough support to increase the winds to 35 kt, \nmaking the depression Tropical Storm Polo. \n\nIt remains tricky to find the center this evening, but my best guess \nis that the center is close to the ongoing convective burst and is \nestimated to be moving east-northeastward or 075 degrees at 4 kt. \nOver the next 24-36 h, Polo will likely be influenced by the \nsteering of low- to mid-level ridging south of the cyclone, with \nmost of the track guidance showing a slow eastward or \neast-southeastward motion on Monday. On Tuesday, mid-level ridging \nover Texas and Mexico is forecast to build in, and the track \nguidance responds to this change by showing a sharp, hairpin turn to \nthe northwest that continues through the remainder of the forecast \nperiod. The NHC track forecast is close to the prior one, though \nshows a bit of a sharper turn in 48-60 h, and is a little to the \nsouth and west thereafter. This track forecast roughly splits the \ndifference between the reliable HFIP Corrected Consensus Approach \n(HCCA) and Google DeepMind ensemble mean (GDMI) aids. It is worth \nnoting some of the hurricane-regional models are further east, and \nshort-term trends will be monitored in the guidance over the next \nday or so to see if any eastward adjustments are needed. Towards the \nend of the forecast, it is possible Polo may get close enough to the \ncirculation of Odalys to interact, and there is significant track \nuncertainty in 5 days. \n\nIntensity-wise there appear to be few impediments in Polo's \nforecast, with low shear under 10 kt, very warm 31 C sea-surface \ntemperatures, and abundant deep-layer moisture.  While it may take \nanother 12 h or so for Polo to develop an inner core, its possible \nthe ongoing convective burst near the center is already initiating \nthat process. The intensity guidance is rather aggressive, with all \nof the hurricane-regional models showing various degrees of rapid \nintensification over the next 2-3 days in addition to the HCCA and \nGDMI guidance. Thus, the NHC intensity forecast will also show rapid \nintensification in the 24-60 h period, and now shows Polo becoming a \nCategory 4 hurricane in 72 h. Remarkably, this is still under the \nlatest HCCA and GDMI intensity in that time frame and its possible \nfuture upward intensity adjustments will be needed. Thereafter, \ninner-core fluctuations will likely govern the intensity of Polo in \nthe 3-5 day time frame, but Polo is still likely to be a major \nhurricane through the end of the forecast period. \n\n \nKey Messages:\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. Tropical Storm Polo is forecast to strengthen and move closer to \nthe southwestern Mexican coast as a major hurricane later this week. \nAlthough it is too soon to determine the exact location or magnitude \nof impacts associated with the system, interests in Mexico should \nclosely monitor its progress and updates to the forecast.\n \n \nFORECAST POSITIONS AND MAX WINDS\n \nINIT  21/0300Z 15.1N 104.6W   35 KT  40 MPH\n 12H  21/1200Z 15.4N 103.8W   45 KT  50 MPH\n 24H  22/0000Z 15.4N 103.1W   60 KT  70 MPH\n 36H  22/1200Z 15.2N 102.4W   80 KT  90 MPH\n 48H  23/0000Z 15.5N 102.4W   95 KT 110 MPH\n 60H  23/1200Z 16.0N 103.0W  110 KT 125 MPH\n 72H  24/0000Z 16.7N 103.7W  115 KT 130 MPH\n 96H  25/0000Z 18.2N 106.0W  115 KT 130 MPH\n120H  26/0000Z 19.5N 109.5W  115 KT 130 MPH\n \n"}