Issued at 200 PM MST Tue Sep 30 2025
000 WTPZ45 KNHC 302044 TCDEP5 Tropical Storm Octave Discussion Number 3 NWS National Hurricane Center Miami FL EP152025 200 PM MST Tue Sep 30 2025 Octave continues to become a little better organized this afternoon, with curved bands forming primarily along the southwestern side of the small cyclone. The wind field appears so small that scatterometer data largely missed the small circulation in the narrow 100 n mi gap between passes. The latest subjective Dvorak intensity estimates were T3.0/45 kt from SAB, and T2.5/35 kt from TAFB. The initial intensity is raised to 40 kt this advisory, a blend of the two estimates, and near the latest ADT estimate of T2.8/41 kt and D-PRINT estimate of 40 kt. Octave is still moving northwestward, with the latest motion estimated at 320/4 kt. A turn more to the north-northwest is anticipated over the next day or so as Octave interacts with the remnant low-level vorticity of another small disturbance that is passing the system by to the north. Most of the guidance shows Octave quickly absorbing the weaker system, and after that is complete, low to mid-level ridging builds back in, resulting in the cyclone turning back west-northwestward from 36-72 h. Towards the end of the forecast, steering currents are expected to collapse as a longwave trough erodes the mid-level ridging and low-level monsoonal flow becomes more established to the east of Octave. Compared to the previous cycle, the track guidance has trended westward, and the NHC track forecast has been shifted a little farther west early on, but more substantially by the end of the forecast period, though it remains east of the latest HCCA and Google DeepMind ensemble mean (GDMI). The tropical storm has been able to intensify a little today despite being under 20-25 kt of east-northeasterly vertical wind shear. This shear is expected to persist for the next 36-48 hours, and thus only a slight bit of additional intensification is expected tonight followed by a pause in strengthening. After 60 h, Shear is expected to decrease to 10-15 kt, and how much the storm is able to intensify will be related to its structural characteristics. Octave is expected to remain a small tropical cyclone, so its possible it could be prone to more rapid intensity changes (both up or down) than shown here. For now, the intensity was bumped up a little towards the end of the forecast period, but remains much lower than some of the more aggressive hurricane-regional model guidance (HWRF, HAFS-A) which develop an inner core with Octave much sooner than the remainder of the guidance. The NHC intensity forecast is closest to the HFIP corrected consensus approach (HCCA). FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 10.2N 113.9W 40 KT 45 MPH 12H 01/0600Z 10.8N 114.0W 45 KT 50 MPH 24H 01/1800Z 12.0N 114.5W 45 KT 50 MPH 36H 02/0600Z 12.6N 115.3W 45 KT 50 MPH 48H 02/1800Z 13.0N 116.6W 45 KT 50 MPH 60H 03/0600Z 13.6N 117.9W 45 KT 50 MPH 72H 03/1800Z 14.0N 119.3W 50 KT 60 MPH 96H 04/1800Z 14.5N 120.7W 55 KT 65 MPH 120H 05/1800Z 15.5N 121.0W 55 KT 65 MPH $$ Forecaster Papin
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