Tropical Cyclone Discussion
807 WTPZ45 KNHC 131459 TCDEP5 Hurricane Simon Discussion Number 25 NWS National Hurricane Center Miami FL EP202026 800 AM MST Tue Oct 13 2026 Small stubborn Simon continues to defy expectations this morning. First light visible satellite imagery shows the hurricane still has a small eye, and is also located farther south than was analyzed by satellite imagery last night. This is further supported by microwave images from AMSR-3 at 09 UTC and SSMIS at 1125 UTC which both show an eyewall that is little better organized, though it remains open on the west side. This structure could be due to some residual shear or dry air that was ingested into the circulation. Satellite intensity estimates are all over the place this morning, ranging from as low as 47 kt from UW-CIMSS ADT, and as high as 95 kt by SATCON. Given the small eye signature surrounded by -65 to -70 C cold cloud tops, the initial intensity will be held at 80 kt, on the upper side of these estimates, but should be considered more uncertain than usual. Simon continues to move south of the previous forecast track, and the initial motion is a slow westward drift at 270/2 kt. The farther south initial position and current motion necessitates some pretty significant changes to the short-term track forecast. As mentioned yesterday, Simon is very close to a saddle point, or col, in the deep-layer steering flow. This feature means that Simon's future track is very sensitive to which side of the saddle point the storm is located. Yesterday, a plurality of the guidance was maintaining Simon on a northwestward to northward track, causing it to be on the north side of the saddle point, resulting in continued poleward motion. However, Simon has gained very little latitude over the past 24 h, and thus now finds itself on the south side of the saddle point. Consequently, the track guidance over the past few cycles has shifted substantially southward. The NHC track forecast is now shifted in a similar fashion, showing a very slow motion over the next 36-48 h as Simon makes a small cyclonic loop. The first part of the track forecast is substantially farther south than the prior one, but still not as far south as the HFIP Corrected Consensus Approach (HCCA), or any of the latest hurricane-regional models. After 48 h, deep-layer steering finally begins to shift out of the south as a deep-layer cutoff low digs into southern California, and Simon will finally start moving northward in earnest during the 48-72 h time frame. Towards the end of the forecast, Simon could bend back more north-northwestward, potentially entering the Gulf of California and finally making landfall in Mexico between 96-120 h. However, this forecast should be considered very low confidence at that time frame, as there are a host of solutions from landfall in mainland Mexico even before reaching the Gulf of California, direct impacts to Baja California Sur, or solutions that stay south of Mexico entirely over the next 5 days. The intensity forecast is not much easier either. Simon has managed to maintain a small inner-core and hurricanes of this size are known to be sensitive to small changes in their environmental conditions that could result in rapid changes in intensity, either up or down. This is also exhibited in the intensity guidance this morning, which ranges from Simon weakening to a tropical depression all the way to it regaining major hurricane intensity over the next 48-60 h. While shear over Simon is expected to remain low for the next 48 h and sea-surface temperatures (SSTs) are in the 29-30 C range, one wild card is how Simon's slow motion might cause some cool ocean upwelling. There is one ocean glider providing subsurface ocean temperature data near Simon, and it depicts 28 C waters down to about 80 m below the ocean surface. Assuming Simon does not completely stall, this is likely to support it maintaining hurricane intensity for the next 48-72 h. Given all this information, the NHC intensity forecast will show Simon maintaining its intensity as an 80 kt hurricane for the next 48 h. Afterwards, southwesterly vertical wind shear is forecast to increase in earnest, and the small Simon is forecast to quickly weaken even as it moves over warmer SSTs. This latest forecast is initially on the high side of the guidance above HCCA, but not as high as the latest HAFS-A, COAMPS-TC, or HMON runs. After 48 h this forecast falls back to the middle of the guidance envelope. It is worth stressing that this is a very low confidence forecast for both track and intensity, and interests in west-central Mexico and Baja California Sur should continue to closely monitor the latest updates. Changes to watches and warnings could be required later today based on the latest forecast trends. Key Messages: 1. Simon could approach Las Islas Marias on Wednesday and the coast of western Mexico later this week at or near hurricane strength, and a Hurricane Watch is in effect for a portion of these areas. Interests in west-central Mexico and Baja California Sur should continue to closely monitor the latest updates to Simon's forecast. Changes to watches and warnings could be required later today based on the latest forecast trends. 2. Large swells will affect portions of the southwestern and west-central coasts of Mexico over the next several days. These swells are likely to cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 20.3N 107.3W 80 KT 90 MPH 12H 14/0000Z 20.3N 107.6W 80 KT 90 MPH 24H 14/1200Z 20.3N 107.8W 80 KT 90 MPH 36H 15/0000Z 20.1N 107.9W 80 KT 90 MPH 48H 15/1200Z 20.1N 107.7W 80 KT 90 MPH 60H 16/0000Z 21.0N 107.8W 75 KT 85 MPH 72H 16/1200Z 22.8N 108.2W 70 KT 80 MPH 96H 17/1200Z 25.2N 109.6W 55 KT 65 MPH 120H 18/1200Z 28.5N 110.5W 30 KT 35 MPH...POST-TROP/INLAND