372
WTNT45 KNHC 230237
TCDAT5
HURRICANE TAMMY DISCUSSION NUMBER 19
NWS NATIONAL HURRICANE CENTER MIAMI FL AL202023
1100 PM AST SUN OCT 22 2023
SATELLITE IMAGES SHOW THAT TAMMY HAS NOT BECOME BETTER ORGANIZED
OVER THE PAST SEVERAL HOURS. IN FACT, THE CENTRAL DENSE OVERCAST
(CDO) HAS BECOME MORE FRAGMENTED IN APPEARANCE AND THE CENTER
APPEARS TO BE NEAR THE SOUTHERN PORTION OF THE CDO. THERE ARE
HOWEVER A COUPLE OF PROMINENT CONVECTIVE BANDS OVER THE EASTERN
PORTION OF THE CIRCULATION. UPPER-LEVEL OUTFLOW IS RESTRICTED OVER
THE SOUTHERN SEMICIRCLE OF THE SYSTEM, SUGGESTING THE INFLUENCE OF
SOUTHERLY VERTICAL WIND SHEAR. SFMR-OBSERVED SURFACE WINDS FROM A
NOAA HURRICANE HUNTER AIRCRAFT CONDUCTING A RESEARCH MISSION INTO
TAMMY SUPPORT A CURRENT INTENSITY OF 70-75 KT, SO THE ADVISORY
INTENSITY ESTIMATE IS UNCHANGED.
A CENTER POSITION ESTIMATE FROM THE AIRCRAFT INDICATES THAT THE
MOTION REMAINS NORTHWESTWARD, OR 325/8 KT AT THIS TIME. THE
CYCLONE SHOULD TURN NORTHWARD TO NORTHEASTWARD OVER THE NEXT 72
HOURS OR SO WHILE MOVING AROUND THE WESTERN SIDE OF A MID-LEVEL
SUBTROPICAL HIGH. LATER IN THE FORECAST PERIOD, TAMMY SHOULD BEGIN
TO INTERACT WITH A CYCLONIC CIRCULATION THAT CUTS OFF FROM AN
EASTWARD-MOVING MID-LATITUDE TROUGH OVER THE WESTERN ATLANTIC.
THIS SHOULD CAUSE THE SYSTEM TO TURN WESTWARD AROUND THE NORTHERN
SIDE OF THE LARGER CIRCULATION IN 3-5 DAYS. THERE CONTINUES TO BE
A FAIRLY LARGE SPREAD IN THE TRACK GUIDANCE IN THIS TIME FRAME,
HOWEVER.
THE DYNAMICAL GUIDANCE INDICATES THAT TAMMY WILL BE IN AN
ENVIRONMENT OF SIGNIFICANT SOUTH-SOUTHWESTERLY VERTICAL WIND SHEAR
FOR THE NEXT FEW DAYS. THIS NEGATIVE INFLUENCE COULD BE
COUNTERACTED SOMEWHAT BY THE PRESENCE OF A MOIST AND UNSTABLE
AIR MASS ALONG WITH WARM OCEAN WATERS. THEREFORE SOME SLIGHT
STRENGTHENING IS STILL PREDICTED, ALONG THE LINES OF THE
DECAY-SHIPS MODEL. THIS IS ALSO SIMILAR TO THE PREVIOUS OFFICIAL
INTENSITY FORECAST. BY DAY 4, TAMMY SHOULD BEGIN TO MERGE WITH A
BAROCLINIC ZONE AND SIMULATED SATELLITE IMAGERY FROM THE GFS AND
ECMWF MODELS DEPICT A FRONTAL APPEARANCE. THEREFORE THE SYSTEM IS
FORECAST TO HAVE BECOME EXTRATROPICAL BY 96 HOURS.
KEY MESSAGES:
1. HEAVY RAIN FROM TAMMY WILL REMAIN POSSIBLE OVER THE BRITISH
VIRGIN ISLANDS, LEEWARD ISLANDS, AND NORTHERN WINDWARD ISLANDS INTO
MONDAY MORNING. THIS RAINFALL MAY PRODUCE ISOLATED FLASH AND URBAN
FLOODING, ALONG WITH ISOLATED MUDSLIDES IN AREAS OF HIGHER TERRAIN.
FORECAST POSITIONS AND MAX WINDS
INIT 23/0300Z 20.8N 64.0W 75 KT 85 MPH
12H 23/1200Z 21.5N 63.9W 75 KT 85 MPH
24H 24/0000Z 22.5N 63.4W 80 KT 90 MPH
36H 24/1200Z 23.2N 62.6W 80 KT 90 MPH
48H 25/0000Z 24.0N 61.6W 80 KT 90 MPH
60H 25/1200Z 25.3N 60.4W 80 KT 90 MPH
72H 26/0000Z 26.6N 59.5W 75 KT 85 MPH
96H 27/0000Z 29.6N 60.5W 60 KT 70 MPH...POST-TROP/EXTRATROP
120H 28/0000Z 30.5N 64.5W 50 KT 60 MPH...POST-TROP/EXTRATROP
FORECASTER PASCH
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