Tropical Cyclone Discussion
052 WTPZ44 KNHC 240851 TCDEP4 Tropical Storm Iselle Discussion Number 4 NWS National Hurricane Center Miami FL EP092026 200 AM PDT Mon Aug 24 2026 Iselle is being affected by northwesterly shear, with much of the deep convection displaced to the south and east of the center. Over the past several hours, the convective structure has evolved, with curved banding becoming increasingly established around the center. The latest Dvorak intensity estimate from TAFB at 0600 UTC was 3.0/45 kt; however, recent objective intensity estimates from UW-CIMSS have increased and range from 43-59 kt. Given the improved banding evident on satellite imagery and the upward trend in objective intensity estimates, the initial intensity is set at 50 kt for this advisory. The tropical storm is moving northwestward around 10 kt, steered by a mid-level ridge centered over the southwestern United States. Iselle is forecast to turn toward the west-northwest as the ridge expands westward into the eastern Pacific, and this general motion is expected through much of this week. The latest NHC forecast is very similar to the previous advisory and lies near the middle of the track guidance envelope, closest to the HFIP Corrected Consensus (HCCA) and the Google DeepMind (GDMI) model. There is considerable spread among the guidance during the latter portion of the forecast period, resulting in slightly below-average confidence in the track forecast. Iselle is moving over warm waters around 29-30 C and remains within a fairly moist mid-level environment, which should support gradual strengthening during the next 12-24 h. The latest NHC forecast brings Iselle to hurricane strength during this period, near the upper end of the intensity guidance, and is consistent with HCCA and GDM. Beyond 24 h, increasing wind shear, cooler waters and progressively drier mid-level air are expected to lead to gradual weakening from Tuesday through the remainder of the week. The ECMWF and GFS simulated satellite imagery suggest that Iselle may struggle to maintain organized convection by late this week, raising the possibility that the cyclone could become post-tropical earlier than currently forecast. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 17.8N 116.2W 50 KT 60 MPH 12H 24/1800Z 19.0N 117.4W 60 KT 70 MPH 24H 25/0600Z 20.1N 118.9W 65 KT 75 MPH 36H 25/1800Z 20.9N 120.7W 60 KT 70 MPH 48H 26/0600Z 21.5N 122.5W 55 KT 65 MPH 60H 26/1800Z 21.9N 124.4W 50 KT 60 MPH 72H 27/0600Z 22.4N 126.3W 45 KT 50 MPH 96H 28/0600Z 23.1N 130.1W 35 KT 40 MPH 120H 29/0600Z 23.9N 134.1W 30 KT 35 MPH...POST-TROP/REMNT LOW