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Tropical Storm OCTAVE Forecast Discussion Number 4
2013-10-13 22:46:08| National Hurricane Center (East Pacific)
Issued at 200 PM PDT SUN OCT 13 2013 000 WTPZ45 KNHC 132046 TCDEP5 TROPICAL STORM OCTAVE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP152013 200 PM PDT SUN OCT 13 2013 DURING THE PAST 6 HOURS...OUTER BAND CONVECTION HAS DISSIPATED WHILE INNER CORE CONVECTION HAS MADE SOMEWHAT OF A COMEBACK. THE INNER CORE CONVECTION NOW CONSISTS OF A SMALL RING OF CONVECTION ABOUT 100 NMI IN DIAMETER WITH A 25 NMI DIAMETER EYE FEATURE EMBEDDED NEARLY IN THE CENTER OF THE CONVECTIVE RING. HOWEVER...SEVERAL PASSIVE MICROWAVE IMAGES INDICATE THAT THE MID-/UPPER-LEVEL EYE FEATURE IS TILTED MORE THAN 20 NMI TO THE NORTH OF THE LOW-LEVEL CENTER. SATELLITE INTENSITY ESTIMATES HAVE JUMPED SHARPLY TO T4.0/65 KT FROM TAFB AND T3.5/55 KT FROM SAB SINCE THE PREVIOUS ADVISORY...BUT A 1639Z ASCAT-B OVERPASS ONLY REVEALED 35-40 KT WINDS WITHIN 20 NMI EAST OF THE CENTER...AND A 1725Z ASCAT-A OVERPASS ONLY INDICATED 45 KT IN THE EASTERN EYEWALL. THIS SUGGESTS THAT OCTAVE MIGHT NOT BE AS STRONG AS THE SATELLITE SIGNATURES INDICATE. THE INITIAL INTENSITY BLENDS THESE ESTIMATES AND IS GENEROUSLY SET TO 55 KT. UW-CIMSS SHEAR ANALYSES INDICATE THAT OCTAVE IS EXPERIENCING 15-20 KT OF SOUTHERLY MID-LEVEL SHEAR THAT IS UNDERCUTTING THE OTHERWISE FAVORABLE 6 KT OF 850-200 MB SHEAR... WHICH EXPLAINS THE NORTHWARD TILT OF THE EYE FEATURE. SOME ADDITIONAL STRENGTHENING IS POSSIBLE DURING THE NEXT 12 HOURS OR SO...BUT THE TILTED EYE FEATURE...ALONG WITH THE RATHER COMPACT SIZE OF THE CYCLONE...MEANS THE OCTAVE SHOULD QUICKLY WEAKEN ONCE IT MOVES OVER MUCH COOLER WATERS IN ABOUT 18-24 HOURS. AFTER THAT...STEADILY INCREASING SOUTHWESTERLY SHEAR SHOULD DECOUPLE THE LOW- AND UPPER-LEVEL CIRCULATIONS...RESULTING IN OCTAVE BECOMING A REMNANT LOW BY 96 HOURS...IF NOT SOONER. THE INITIAL MOTION ESTIMATE IS 335/11 KT. OCTAVE SHOULD CONTINUE TO MOVE AROUND THE WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE THROUGHOUT THE FORECAST PERIOD. THE CYCLONE SHOULD GRADUALLY SLOW DOWN AND TURN NORTHWARD BY MONDAY AND TOWARD THE NORTH-NORTHEAST AND NORTHEAST ON TUESDAY. BY WEDNESDAY...A VERTICALLY SHALLOW AND WEAK OCTAVE COULD BECOME NEARLY STATIONARY AS IT APPROACHES THE SOUTHWESTERN COAST OF THE BAJA CALIFORNIA AND COMPLETELY DECOUPLES. THE MID-/UPPER-LEVEL CIRCULATIONS AND THE ASSOCIATED MOISTURE PLUME...HOWEVER...SHOULD CONTINUE TO MOVE NORTHEASTWARD AND SPREAD LOCALLY HEAVY RAINS ACROSS BAJA AND NORTHERN MEXICO AND INTO THE SOUTHWESTERN U.S. THE NHC FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK...AND IS CLOSE TO A BLEND OF THE TCVE AND FSSE MODELS. DESPITE THE RECENT STRENGTHENING OF OCTAVE...THE CURRENT TRACK AND INTENSITY FORECASTS...PLUS AVAILABLE INTENSITY GUIDANCE...DOES NOT WARRANT ANY TROPICAL STORM WATCHES OR WARNINGS FOR THE BAJA CALIFORNIA PENINSULA. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 19.2N 112.7W 55 KT 65 MPH 12H 14/0600Z 20.6N 113.5W 55 KT 65 MPH 24H 14/1800Z 22.3N 113.7W 45 KT 50 MPH 36H 15/0600Z 23.7N 113.6W 35 KT 40 MPH 48H 15/1800Z 24.6N 113.2W 30 KT 35 MPH 72H 16/1800Z 25.1N 113.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 17/1800Z 26.0N 112.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 18/1800Z...DISSIPATED $$ FORECASTER STEWART
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