Issued at 800 AM MST Tue Sep 30 2025
000 WTPZ45 KNHC 301444 TCDEP5 Tropical Storm Octave Discussion Number 2 NWS National Hurricane Center Miami FL EP152025 800 AM MST Tue Sep 30 2025 The convective structure of the depression has continued to improve this morning, with cold cloud tops (-80C CMG) developing over the surface center, and a deep convective curved band located in the east semicircle of the cyclone. Subjective Dvorak intensity estimates from TAFB and SAB are T2.0 and T3.0, and the UW-CIMSS objective intensity analyses range from 34-39 kt. Based on a blend of these data and the cyclone's improved satellite presentation, the initial intensity is raised to 35 kt, upgrading Tropical Depression Fifteen-E to Tropical Storm Octave. Although Octave should remain over warm oceanic surface temperatures, and move within a surrounding environment with ample low- to mid-level moisture, moderate deep-layer east-northeasterly shear is expected to hamper significant development. Accordingly, the forecast reflects little change in strength through Thursday. Afterward, the statistical Decay-SHIPS intensity guidance and the global models indicate that the shear will diminish some, allowing for some additional intensification through day 5, and the intensity forecast follows suit. Octave's initial motion is estimated to be northwestward, or 325/4 kt. The cyclone is forecast to turn north-northwestward to northward later today in response to a mid-tropospheric cut-off low drifting southward toward Octave. Beyond the 60 hour period, model guidance indicates that a subtropical ridge will build to the north of the cyclone and induce a west-northwestward motion through Saturday, while the cut-off mentioned above weakens and ultimately dissipates. By day 5, the global models agree that Octave will slow in forward speed and gradually turn toward the northwest and north-northwest, while the ridge to the north of the cyclone erodes. The NHC forecast lies close to the various consensus aids and has been shifted a bit to the right of the previous forecast after 36 hours. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 9.9N 113.5W 35 KT 40 MPH 12H 01/0000Z 10.4N 113.7W 35 KT 40 MPH 24H 01/1200Z 11.3N 114.0W 40 KT 45 MPH 36H 02/0000Z 12.3N 114.3W 40 KT 45 MPH 48H 02/1200Z 12.9N 115.2W 40 KT 45 MPH 60H 03/0000Z 13.4N 116.3W 40 KT 45 MPH 72H 03/1200Z 13.8N 117.5W 45 KT 50 MPH 96H 04/1200Z 14.6N 119.5W 45 KT 50 MPH 120H 05/1200Z 15.6N 119.8W 50 KT 60 MPH $$ Forecaster Roberts
