{"id": "1217573366913531911", "title": "Tropical Cyclone Discussion", "adv_date": "2026-10-10T15:00:00Z", "msg": "544\nWTPZ45 KNHC 101458\nTCDEP5\n \nHurricane Simon Discussion Number  13\nNWS National Hurricane Center Miami FL       EP202026\n900 AM CST Sat Oct 10 2026\n \nSimon has gone through some inner-core structural changes over the \nlast 6 to 12 hours. After exhibiting a pinhole eye for much of \nyesterday on geostationary satellite, the more recent imagery this \nmorning shows a somewhat larger eye that cleared out briefly at \naround 10 UTC. This structure suggests that Simon may have undergone \nan eyewall replacement cycle (ERC) overnight. A couple of microwave \nimages that became available after the last advisory also show this \nsomewhat larger eye. Since that time, the eye has become more \nclouded over again. The initial intensity is being held at 130 kt \nthis advisory, given little change in the satellite intensity \nestimates since the intermediate advisory. An Air Force Reserve \nreconnaissance mission is scheduled for Simon this afternoon and \nwill hopefully provide more in-situ data on the hurricane's \nstructure and intensity later today. \n \nThe hurricane took a bit of a northwestward jog and slowed to a \ncrawl since the previous advisory, but the longer-term estimated \nmotion is just west of due north at 350/3 kt. The hurricane is being \nprimarily steered by a weak mid-level ridge centered to its east, \nwhich is providing deep-layer southerly flow. Another deep-layer \ntrough lies well to the northwest of Simon (which is picking up \nRachel) but appears too far away to impart much steering, with a \nnarrow mid-level ridge parked just south of the Baja California \nPeninsula providing light northerly flow. The net effect is that \nSimon should continue to move northward, but at a rather slow \nforward speed. In fact, the track guidance this cycle has slowed \ndown a little more compared to the previous cycle, and the NHC track \nis a little slower and a bit further west in the short-term due to \nthe initial position adjustment. This current track forecast still \ntakes the hurricane inland over the Mexican state of Jalisco in \n24-36 h. However, it is worth stressing there is still a notable \namount of track uncertainty, with the ECMWF, HAFS-A, and Google \nDeepMind Ensemble mean (GDMI) keeping Simon just offshore of the \nMexican coast for the next 48 h, while the GFS, HAFS-B, HWRF, and \nHMON models show Simon moving inland in the next 24-36 h. The latest \nGoogle Weather Next model (WN3I) attempts to split the difference \nbetween these solutions and brushes right up along the Mexico \ncoastline. The NHC track still remains a bit of the east side of the \nguidance envelope overall, as there is a pretty well-known bias that \ntropical cyclones in this area tend to track east of the forecast \ntrack due to interaction with the high topography of coastal Mexico. \n\nThe future intensity forecast of Simon is also largely influenced by \nthis track uncertainty. Environmental conditions remain very \nfavorable, and Simon's intensity will likely be controlled by \ninner-core related fluctuations today. However, as Simon approaches \nthe coast of Mexico, the higher terrain will likely start to impinge \non its outer circulation, where downslope subsidence may start to \noccur. This terrain effect will likely cause its wind field core to \nshrink in size and ultimately result in some weakening, even before \nthe hurricane moves near or onshore of the Mexican coastline. Thus, \nweakening is now shown in 24 h, with more substantial weakening \noccurring after Simon's core is forecast to move onshore. It is \nworth stressing that this intensity forecast contains a lot of \nuncertainty, and if Simon remains offshore, it could remain stronger \nthan shown in this forecast. This scenario is highlighted by the   \n06 UTC HAFS-A forecast which keeps Simon a significant hurricane \nsince it remains just offshore. Ultimately, the intensity forecast \nremains quite similar to the prior one after land interaction \nbegins, with Simon expected to dissipate over the higher terrain of \nMexico after 60 h.\n \nKey Messages:\n \n1. Catastrophic wind and life-threatening storm surge impacts are \nlikely along a portion of the west-central coast of Mexico, and a \nHurricane Warning is in effect from Punta San Telmo to El Roblito. \nPreparations to protect life and property should be completed today.\n \n2. Heavy rainfall associated with Simon will impact portions of\nsouthwestern Mexico through this weekend. This rainfall will produce\nlife-threatening flooding and mudslides, especially in areas of\nsteep terrain.\n \n3. Swells will affect portions of the southwestern and west-central\ncoast of Mexico through the weekend. These swells are likely to\ncause life-threatening surf and rip current conditions. Please\nconsult products from your local weather office.\n \n \nFORECAST POSITIONS AND MAX WINDS\n \nINIT  10/1500Z 17.4N 104.8W  130 KT 150 MPH\n 12H  11/0000Z 18.1N 105.0W  135 KT 155 MPH\n 24H  11/1200Z 19.1N 105.2W  125 KT 145 MPH\n 36H  12/0000Z 20.4N 105.4W   80 KT  90 MPH...INLAND\n 48H  12/1200Z 21.7N 105.4W   55 KT  65 MPH...INLAND\n 60H  13/0000Z 23.0N 105.5W   30 KT  35 MPH...POST-TROP/INLAND\n 72H  13/1200Z...DISSIPATED\n \n"}