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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