Tropical Cyclone Discussion
653 WTPZ45 KNHC 122053 TCDEP5 Hurricane Simon Discussion Number 22 NWS National Hurricane Center Miami FL EP202026 200 PM MST Mon Oct 12 2026 This afternoon, Simon is a small hurricane that is dealing with some easterly vertical wind shear. The inner-core continues to produce a lot of lightning but mostly in the eastern semicircle. The most recent microwave image was a 1718 UTC AWS pass that also showed this core asymmetry with the eyewall open on the northwest side on the 180 GHz channel. While the latest 18 UTC subjective Dvorak estimate remains at CI 5.5/102-kt, the objective intensity estimates from UW-CIMSS continue to gradually decrease. Thus, the initial intensity is being reduced to a somewhat uncertain 85 kt this advisory, which also matches the D-MINT mean estimate from the AWS microwave pass above. A helpful 1712 UTC Metop-C scatterometer pass was useful to help adjust Simon's radii and also to indicate its wind field has become quite small, with 34-kt winds only extending out about 40 n mi. Simon's track has thrown us a few curve balls over the past 24-36 h, and this afternoon is no exception as the hurricane made a brief westward jog, with the longer-term motion estimated at 290/3 kt. The track forecast remains problematic. Part of the slow motion Simon is exhibiting today is related to competing steering synoptic features, primarily a mid-level ridge centered near the Texas Coast versus another mid-level ridge located southwest of the hurricane. The influence of the northeastern ridge has been a little stronger, but steering diagnostics suggest that Simon may be soon reaching a bifurcation or COL point in the flow. This feature indicates the area where the net steering flow collapses and helps explain why both the deterministic and ensemble track guidance spread increases quite dramatically in 24 to 48 h. For example, the HAFS-A/B models, which earlier this morning were showing a faster northeastward turn back into Mexico, now show Simon stalling and executing a slow cyclonic loop in the waters between mainland Mexico and the southern tip of the Baja California Peninsula. The European ensemble spread suggests that these individual solutions are likely just different flavors of the overall distribution, which is spread out in a southwest to northeast fashion. While the overall track guidance continues to have large spread, there has been a northward and faster shift this cycle. This shift is a bit odd given the current storm motion, so the NHC track forecast is initially on the left side of the guidance over the first 12-24 h, but falls back closer to the middle of the guidance envelope, and attempts to blend the latest HFIP Corrected Consensus Approach (HCCA), Google Deepmind ensemble mean (GDMI), and their latest Weather Next model (WN3I). Ultimately the latest track forecast converges close to the prior one near landfall in Mexico in 72-96 h, but this remains a low confidence track forecast. The intensity forecast for Simon is also challenging. The current mid-level easterly shear affecting Simon's inner core structure has not been well anticipated by the model guidance. Small tropical cyclones like Simon are often more sensitive to negative environmental factors, and even 15-20 kt of easterly shear could be enough to disrupt the core structure, especially with nearby environmental dry air. The factors may result in additional weakening in the short-term. However, EC-SHIPS guidance shows the shear lowering below 5 kt in 24-48 h. Assuming Simon is able to maintain an inner core structure and take advantage of the more favorable conditions, restrengthening is still forecast, especially as the hurricane is expected to track over the warmest sea-surface temperatures in the Eastern Pacific basin (31-32 C). The intensity guidance shows more short-term weakening compared to the previous cycle, and the NHC intensity forecast is lower early on, but still shows restrengthening as Simon encounters those more favorable conditions, and ends up on the high end of the intensity guidance in 60-72 h. Small storms like Simon can also be prone to rapid changes in intensity, which continues to make this intensity forecast also more uncertain than usual. Rapid weakening is still anticipated when Simon eventually makes landfall in the latter part of this week between 72-96 h. Key Messages: 1. Hurricane conditions are likely on Las Islas Marias over the next day or so, where a Hurricane Warning remains in effect. 2. Simon is expected to approach the coast of western Mexico later this week, where hurricane conditions are possible. A Hurricane Watch is in effect from Cabo Corrientes to Bahia Tempehuaya. 3. Heavy rainfall associated with Simon will impact portions of west-central Mexico over the next few days. This rainfall will produce life-threatening flooding and mudslides, especially in areas of steep terrain. 4. Large swells will affect portions of the southwestern and west-central coasts of Mexico over the next few days. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 20.2N 106.8W 85 KT 100 MPH 12H 13/0600Z 20.5N 107.0W 75 KT 85 MPH 24H 13/1800Z 20.9N 107.5W 65 KT 75 MPH 36H 14/0600Z 21.2N 107.7W 70 KT 80 MPH 48H 14/1800Z 21.5N 107.7W 75 KT 85 MPH 60H 15/0600Z 22.2N 107.4W 80 KT 90 MPH 72H 15/1800Z 23.0N 107.0W 85 KT 100 MPH 96H 16/1800Z 24.2N 106.6W 30 KT 35 MPH...POST-TROP/INLAND 120H 17/1800Z...DISSIPATED