Issued at 800 PM MST Tue Sep 30 2025
706 WTPZ45 KNHC 010257 TCDEP5 Tropical Storm Octave Discussion Number 4 NWS National Hurricane Center Miami FL EP152025 800 PM MST Tue Sep 30 2025 Octave remains a sheared tropical cyclone, with the coldest cloud tops displaced to the south and west of the low-level center. The latest UW-CIMSS shear analysis indicates about 20 kt of east-northeasterly shear over the system. Despite this shear, convection has persisted near the low-level center, and the cyclone continues to exhibit well-defined banding on its southern and western sides. The latest subjective Dvorak intensity estimates from TAFB and SAB are both 3.0/45 kt, while the UW-CIMSS objective estimates have ranged from 33 to 41 kt since the previous advisory. Based on a blend of these data, and given little change in the overall satellite presentation during the past several hours, the initial intensity is held at 40 kt. Octave is estimated to be moving north-northwestward, or 340 degrees at 6 kt. This general motion is expected to continue tonight and Wednesday as the cyclone moves into a weakness in the subtropical ridge created by a disturbance to its north. Once that disturbance is absorbed by Octave’s circulation, a mid-level ridge is forecast to become re-established to the north of the cyclone, steering it westward to west-northwestward from Wednesday night through Saturday. By 120 hours, Octave is expected to slow considerably and turn eastward as a longwave trough approaches from the northwest and the subtropical ridge to its east is eroded by a developing tropical cyclone offshore of southwestern Mexico. The new NHC track forecast is very similar to the previous one through 72 hours and then slightly westward by days 4 and 5, accounting for a westward shift in the latest guidance. The forecast lies near the middle of the guidance envelope, close to the GDMI aid through 72 hours, and roughly midway between the prior track and GDMI aid beyond that time. Octave will remain over warm waters and within a moist environment for the next several days. However, moderate to strong east-northeasterly vertical wind shear is expected to hinder significant intensification. Some slight strengthening is possible tonight, followed by little change in strength during the next couple of days. Modest intensification is forecast by days 3 and 4 as the shear is expected to relax somewhat while the cyclone remains over warm waters. By day 5, slight weakening is anticipated as Octave moves into a drier mid-level environment and over cooler waters near 26C. Confidence in the intensity forecast remains low beyond day 3 due to considerable spread among the guidance. The official forecast is closest to the ECMWF-based SHIPS guidance and is very similar to the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 10.8N 114.4W 40 KT 45 MPH 12H 01/1200Z 11.6N 114.5W 45 KT 50 MPH 24H 02/0000Z 12.5N 115.2W 45 KT 50 MPH 36H 02/1200Z 13.0N 116.4W 45 KT 50 MPH 48H 03/0000Z 13.5N 117.6W 45 KT 50 MPH 60H 03/1200Z 13.9N 119.0W 45 KT 50 MPH 72H 04/0000Z 14.4N 120.5W 50 KT 60 MPH 96H 05/0000Z 15.0N 121.9W 55 KT 65 MPH 120H 06/0000Z 15.8N 121.5W 50 KT 60 MPH $$ Forecaster Jelsema (CPHC)
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