Tropical Cyclone Discussion
787 WTPZ45 KNHC 132059 TCDEP5 Hurricane Simon Discussion Number 26 NWS National Hurricane Center Miami FL EP202026 200 PM MST Tue Oct 13 2026 Simon's structure this afternoon has been more or less steady state as its small eye continues to be discernible on both visible and infrared images. However, the surrounding eyewall cloud top temperatures have warmed a bit this afternoon, though it is unclear if this is a diurnal fluctuation or evidence of some cooler ocean upwelling given its slow motion. The most recent high-resolution microwave image was an WSFM pass at 1338 UTC, which showed a nearly closed eyewall and improvement from earlier imagery. The eye signature can also be picked up on the edge of the Cabo San Lucas, Mexico radar. The D-MINT mean estimate associated with the WSFM pass was 79 kt, and the initial intensity is held at 80 kt this advisory, on the higher end of the intensity estimates. A partial Metop-B scatterometer pass was useful to indicate how compact Simon's wind field has become, with 34-kt winds now only extend out an estimated 30 n mi. The initial motion now appears to be a south of due west drift, or 260 degrees at 2 kt. Compared to this morning, the forecast track reasoning has not changed a ton. The small hurricane is currently just on the south side of a saddle point, or col, in the steering flow. Simon's future track is very sensitive to which side of this point the hurricane is located, with light steering currents prevailing leading to slow motion. In the latest round of guidance, all of the hurricane-regional models show a more substantial southward track this afternoon while Simon remains in very light deep-layer southerly steering. While the ECMWF forecast is further north, it was initialized almost a full degree further north of where Simon was located at 12 UTC, placing it over or just on the north side of the saddle point. The Google Deepmind ensembles, which often favors this initialization, jump north in the short term, which appears unrealistic. Thus, the latest NHC track forecast is going to place a little more weight on the hurricane-regional model tracks which had a better initialization, showing a little more southward motion over the next 24-36 h, albeit as a snail's pace. This track still shows a small cyclonic loop and is south of the previous track forecast. After 48 h, the large-scale synoptic pattern finally begins to change, where a deep-layer cutoff low digs into southern California. This pattern will induce more southerly environmental flow over Simon, and should dislodge it from this very stagnant steering pattern assuming it doesn't move as far south as the HAFS-A/B track aids. The NHC track forecast still shows Simon gaining latitude and turning more north-northwest in 60-72 h and lies closest to the HFIP Corrected Consensus Approach (HCCA) track. This could bring Simon closer to the coast of Baja California Sur as it moves up the Gulf of California. However, there remains a wide variety of track solutions that could verify, from well south of Baja California northward to mainland Mexico over the next 5 days. Simon has maintained a relatively healthy appearance today with a well-organized inner core. As stressed earlier, very small hurricanes like Simon are known to be sensitive to small changes in their environmental conditions that could result in rapid changes in intensity, either up or down. Environmental conditions are favorable, with shear over Simon expected to remain low for the next 48 h with sea-surface temperatures (SSTs) in the 28-30 C range. Assuming Simon does not completely stall and upwell cooler ocean waters, some intensification could occur. With that said, there is an extreme range of intensity solutions over the next 48 h, from intensifying into a Category 4 hurricane (HAFS-A) to weakening to a tropical storm (HMON). Given the current structure, the latest NHC intensity forecast now shows some intensification, but remains well under the latest HAFS-A forecast and is closest to the ECMWF LGEM guidance. After 48 h, southwesterly vertical wind shear is forecast to increase rather quickly, and the small sensitive Simon is forecast to weaken even as it moves over warmer SSTs when it tracks northward. This latest forecast is initially on the high side of the guidance, but falls back to the middle of the guidance envelope after 72 h. It is worth stressing that this remains 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. While mainland Tropical Storm and Hurricane watches have been discontinued, new watches and warnings could be required over the next day or two as Simon's ultimate forecast comes into better focus. 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 over the next day or two 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 13/2100Z 20.2N 107.5W 80 KT 90 MPH 12H 14/0600Z 20.0N 107.8W 85 KT 100 MPH 24H 14/1800Z 19.8N 108.1W 90 KT 105 MPH 36H 15/0600Z 19.5N 108.0W 90 KT 105 MPH 48H 15/1800Z 19.8N 107.6W 85 KT 100 MPH 60H 16/0600Z 21.0N 107.8W 70 KT 80 MPH 72H 16/1800Z 22.6N 108.8W 60 KT 70 MPH 96H 17/1800Z 24.4N 110.2W 45 KT 50 MPH...NEAR BAJA CALIFORNIA 120H 18/1800Z 28.8N 111.1W 30 KT 35 MPH...POST-TROP/INLAND