Tropical Cyclone Discussion
356 WTPZ44 KNHC 232032 TCDEP4 Tropical Storm Iselle Discussion Number 2 NWS National Hurricane Center Miami FL EP092026 200 PM PDT Sun Aug 23 2026 Recent satellite imagery over Iselle shows a shear pattern, with a large area of very deep convection located in the southwest semicircle of Iselle. Visible imagery shows a partially exposed low-level center at the northeast edge of the convection. A recent 23/1748Z ASCAT-C overpass shows an elongated, but well-defined surface circulation, with a radius of maximum winds (RMW) of about 70 nautical miles, with gales in the NE, SE and SW quadrants. There are several 40-45 kt vectors on the south side, and the intensity is increased to 45 kt for this advisory. This is above the latest subjective Dvorak estimate from TAFB, which is T2.5/35 kt. The initial motion estimate is northwestward, or 315 degrees at 14 kt. A continued northwest motion is expected through Monday while Iselle is steered by ridging over the southwestern United States and northwestern Mexico. As the ridge builds in a bit more to the north of the cyclone, a gradual turn toward the west-northwest is expected on Tuesday and Wednesday. The NHC track forecast has been shifted well to the right (or northeast) of the previous forecast through 48 h, mainly due to the farther north initial position and is nearly on top of the previous forecast thereafter. The NHC forecast is very close to the latest HFIP Corrected Consensus (HCCA) model and the Google DeepMind (GDMI). There is still a healthy amount of spread in the track guidance, and confidence in the track forecast is slightly below average. Iselle will be traveling over warm water and within a moist environment with weak to moderate vertical wind shear for the next day or so, but westerly vertical wind shear should increase to the 15-20 kt range by Tuesday or sooner. Strengthening is expected for the next 36 h. Thereafter, Iselle will be moving into a more stable environment, with gradually decreasing sea-surface temperatures, so weakening is expected to begin by Tuesday night or Wednesday. Only small changes have been made to the NHC intensity forecast, which lies between the middle and high end of the guidance envelope for most of the forecast period. Rapid intensification is becoming less likely because the RMW is still large, and the system has at most 36-48 h left to strengthen. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 16.9N 115.1W 45 KT 50 MPH 12H 24/0600Z 18.2N 116.3W 50 KT 60 MPH 24H 24/1800Z 19.6N 117.8W 60 KT 70 MPH 36H 25/0600Z 20.8N 119.4W 65 KT 75 MPH 48H 25/1800Z 21.4N 121.1W 65 KT 75 MPH 60H 26/0600Z 21.9N 122.8W 60 KT 70 MPH 72H 26/1800Z 22.4N 124.6W 50 KT 60 MPH 96H 27/1800Z 23.3N 128.4W 45 KT 50 MPH 120H 28/1800Z 24.2N 132.2W 30 KT 35 MPH...POST-TROP/REMNT LOW