Tropical Cyclone Discussion
214 WTPZ44 KNHC 250843 TCDEP4 Tropical Storm Iselle Discussion Number 8 NWS National Hurricane Center Miami FL EP092026 200 AM PDT Tue Aug 25 2026 The infrared satellite presentation of Iselle remains steady early this morning, featuring an established curved band with very cold cloud tops of -75C to -80C that wraps about halfway around the storm. Moderate westerly wind shear continues to impact the system. Earlier microwave imagery showed an established core north and east of the center, although the western portion of the circulation was less defined. An ASCAT-B pass from earlier tonight indicated maximum winds of 53-56 kt, along with slightly larger 34-kt wind radii in the northeast, southeast and northwest quadrants. Recent objective and subjective Dvorak intensity estimates range from 51-63 kt. Given the steady satellite presentation and ASCAT data, and after blending the subjective and objective intensity estimates, the initial intensity is maintained at 60 kt for this advisory. The ASCAT data also indicated that Iselle is located farther northwest and moving slightly faster than previously estimated. The tropical storm is moving northwestward around 13 kt. A turn toward the west-northwest, accompanied by a slight decrease in forward speed, is expected later today as mid-level ridging currently centered over the southern United States strengthens and expands westward into the eastern Pacific. This general heading is expected to continue over the next several days. The latest NHC track forecast has been shifted slightly to the left and is faster than the previous advisory to account for the adjustment to the initial position. The forecast remains near the middle of the track guidance envelope and is closest to the Google DeepMind Ensemble Mean (GDMI). Iselle is currently moving over warm waters near 28 C and remains within a relatively moist mid-level environment, and has likely reached its peak intensity. As the storm moves west-northwestward, progressively cooler waters, increasing dry mid-level air, continued westerly wind shear and increasingly unfavorable upper-level winds are expected to cause gradual weakening over the next several days. The latest NHC intensity forecast calls for Iselle to weaken to a tropical depression by 60 h, and a post-tropical remnant low by 72 h. However, the ECMWF and GFS simulated satellite imagery suggest that Iselle could struggle to maintain organized deep convection before that time, raising the possibility that the cyclone could become post-tropical earlier than currently forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 20.7N 119.9W 60 KT 70 MPH 12H 25/1800Z 21.3N 121.4W 55 KT 65 MPH 24H 26/0600Z 21.9N 123.2W 50 KT 60 MPH 36H 26/1800Z 22.7N 124.9W 45 KT 50 MPH 48H 27/0600Z 23.4N 126.8W 35 KT 40 MPH 60H 27/1800Z 23.9N 128.8W 30 KT 35 MPH 72H 28/0600Z 24.3N 130.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 29/0600Z...DISSIPATED