403 WTPZ44 KNHC 231446 TCDEP4 Tropical Storm Iselle Discussion Number 1 NWS National Hurricane Center Miami FL EP092026 800 AM MST Sun Aug 23 2026 The area of low pressure that we have been monitoring for the past several days (EP92) has had gale-force winds and sufficiently well-organized convection for the past 12 h or so. The ASCAT-C pass from 23/0517Z showed winds of 40 kt, and that the system did not yet have a well-defined circulation, although it was closer than it was on the previous pass from 12 h earlier. An OSCAT pass a couple hours later around 23/0716Z suggested that the surface circulation was continuing to become better-defined. Since that time, satellite imagery indicates continued consolidation of deep convection over the low-level center, and the system very likely has a well-defined circulation by now. Thus, EP92 is upgraded to Tropical Storm Iselle, and the current intensity is estimated at 40 kt based on the scatterometer data. There have been no other recent microwave passes, and the confidence in the initial position is low. The initial motion is estimated to be west-northwestward, or 300 degrees at 10 kt. A northwestward 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 closely follows the HFIP Corrected Consensus (HCCA) model and the Google DeepMind (GDMI), which is on the northern side of the guidance envelope. There is 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 vertical wind shear for the next couple of days. Only slow intensification is forecast during the next 12 h as the cyclone attempts to consolidate and form a core. Given the favorable environment, steady strengthening is forecast tonight and Monday, and the NHC forecast shows Iselle reaching hurricane strength Monday night. By Tuesday night, a modest increase in west-southwesterly vertical wind shear and decreasing sea-surface temperatures along Iselle's path should lead to gradual weakening. The NHC intensity forecast lies near the intensity consensus and the hurricane regional model solutions. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 15.3N 114.2W 40 KT 45 MPH 12H 24/0000Z 16.5N 115.6W 45 KT 50 MPH 24H 24/1200Z 17.9N 117.2W 55 KT 65 MPH 36H 25/0000Z 19.3N 118.7W 65 KT 75 MPH 48H 25/1200Z 20.5N 120.3W 65 KT 75 MPH 60H 26/0000Z 21.4N 121.9W 60 KT 70 MPH 72H 26/1200Z 22.0N 123.6W 55 KT 65 MPH 96H 27/1200Z 23.0N 127.2W 45 KT 50 MPH 120H 28/1200Z 23.9N 130.8W 35 KT 40 MPH $$ Forecaster Hagen  858 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 $$ Forecaster Hagen  586 WTPZ44 KNHC 240245 TCDEP4 Tropical Storm Iselle Discussion Number 3 NWS National Hurricane Center Miami FL EP092026 800 PM PDT Sun Aug 23 2026 The most recent ASCAT and OSCAT passes have shown that the strongest winds with Iselle are around 40 to 45 kt. UW-CIMSS objective estimates are in the 35-55 kt range, and the most recent TAFB subjective Dvorak estimate is T3.0/45 kt. With all of that data in consideration, the intensity has been held at 45 kt for this advisory. However, recent observations at Isla Clarion have recorded sustained winds around 30 to 35 kt, gusting up to around 40 kt and a surface pressure of 1002 mb. Thus in light of that data, the central pressure for Iselle has been lowered to 999 mb. The initial motion estimate is northwestward, or 310 degrees at 8 kt. A continued northwestward motion is expected through Monday while Iselle is steered by ridging over the southwestern United States and northwestern Mexico. As the ridge builds in some more to the north of the cyclone, a gradual turn toward the west-northwest is expected on Tuesday and Wednesday. The current NHC track is very similar to the previous track, only minor adjustments in speed and location have been made. The track remains very close to the lastest HFIP Corrected Consensus (HCCA) model and the Google DeepMind (GDMI). There is a good amount of spread in the track forecast towards the later portion of the forecast, thus the confidence 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. The current NHC intensity forecast is on the higher end of the guidance, thus it is possible that Iselle might not quite make it to hurricane status. After this period, the cyclone will move into a more hostile environment with stronger shear, colder sea-surface temperatures, and some slightly drier air. As such, the storm should progressively get weaker beyond a couple of days. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 17.1N 115.3W 45 KT 50 MPH 12H 24/1200Z 18.1N 116.4W 50 KT 60 MPH 24H 25/0000Z 19.4N 117.8W 60 KT 70 MPH 36H 25/1200Z 20.4N 119.6W 65 KT 75 MPH 48H 26/0000Z 21.0N 121.4W 60 KT 70 MPH 60H 26/1200Z 21.5N 123.1W 55 KT 65 MPH 72H 27/0000Z 21.9N 125.1W 50 KT 60 MPH 96H 28/0000Z 22.8N 128.8W 40 KT 45 MPH 120H 29/0000Z 23.6N 132.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Katz/Cangialosi