950
WTNT45 KNHC 192055
TCDAT5
TROPICAL STORM TAMMY DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL202023
500 PM AST THU OCT 19 2023
TAMMY HAS NOT BECOME ANY BETTER ORGANIZED SINCE THIS MORNING. THE
CENTER OF THE CYCLONE HAS BECOME PARTIALLY EXPOSED TO THE WEST AND
NORTHWEST OF THE MAIN AREA OF DEEP CONVECTION, AND THERE IS LITTLE
EVIDENCE OF BANDING EXCEPT OVER THE SOUTHEASTERN PORTION OF THE
STORM. AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT HAS BEEN
INVESTIGATING TAMMY THIS AFTERNOON AND HAS REPORTED PEAK 850 MB
FLIGHT-LEVEL WINDS OF 53 KT AND SFMR VALUES OF AROUND 40 KT.
EARLIER SCATTEROMETER DATA REVEALED SOME 40-45 KT VECTORS OVER THE
SOUTHEASTERN PORTION OF THE CIRCULATION. BASED ON THESE DATA, THE
INITIAL INTENSITY IS HELD AT 50 KT FOR THIS ADVISORY.
AFTER TAKING A MORE WESTWARD JOG EARLIER THIS AFTERNOON, THE LATEST
AIRCRAFT FIXES SUGGEST THE WEST-NORTHWESTWARD MOTION HAS RESUMED.
THE LATEST MOTION ESTIMATE IS 285 DEGREES AT 11 KT. TAMMY IS
NEARING THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE OVER THE
CENTRAL ATLANTIC AND THE CYCLONE SHOULD TURN NORTHWESTWARD WITHIN
THE NEXT DAY OR SO. THIS MOTION IS EXPECTED TO BRING THE CENTER OF
TAMMY NEAR OR OVER PORTIONS OF THE LEEWARD ISLANDS LATE FRIDAY AND
SATURDAY. ONCE TAMMY IS NORTH OF THE LEEWARD ISLANDS ON SUNDAY,
IT IS EXPECTED TO TURN NORTHWARD AROUND THE WESTERN SIDE OF THE
AFOREMENTIONED RIDGE. THERE HAS BEEN LITTLE OVERALL CHANGE WITH
THE TRACK GUIDANCE THIS CYCLE. THE GFS AND ECMWF MODELS REMAIN
ALONG THE EASTERN SIDE OF THE GUIDANCE ENVELOPE, WHILE THE MODELS
THAT SHOW LESS STRENGTHENING ARE ALONG THE FAR WESTERN SIDE OF THE
GUIDANCE. THE NHC TRACK FORECAST REMAINS NEARS THE MIDDLE OF THE
GUIDANCE ENVELOPE BETWEEN THE HFIP CORRECTED CONSENSUS AND THE TCVA
SIMPLE CONSENSUS AID.
THE CURRENT STRUCTURE OF TAMMY DOES NOT SUGGEST THAT IT WILL
STRENGTHEN VERY QUICKLY DURING THE NEXT DAY OR SO, BUT WARM SSTS
AND MODERATE VERTICAL SHEAR CONDITIONS COULD ALLOW FOR SOME
MODEST INTENSIFICATION AFTER THAT AND THE NHC OFFICIAL FORECAST
STILL CALLS FOR TAMMY TO BECOME A HURRICANE IN A COUPLE OF DAYS.
AFTER THAT TIME, SOME ADDITIONAL STRENGTHENING IS FORECAST AFTER
TAMMY MOVES NORTH OF THE LEEWARD ISLANDS AND RECURVES OVER THE
CENTRAL ATLANTIC.
KEY MESSAGES:
1. TROPICAL STORM CONDITIONS ARE EXPECTED TO BEGIN IN PORTIONS
OF THE LESSER ANTILLES BEGINNING FRIDAY, WHERE A TROPICAL STORM
WARNING IS IN EFFECT. TROPICAL STORM AND HURRICANE CONDITIONS ARE
POSSIBLE ELSEWHERE IN THE LEEWARD ISLANDS WHERE HURRICANE AND
TROPICAL STORM WATCHES ARE CURRENTLY IN EFFECT. ADDITIONAL WATCHES
AND WARNINGS WILL LIKELY BE REQUIRED TONIGHT.
2. HEAVY RAINS FROM TAMMY WILL BEGIN TO AFFECT THE LEEWARD AND
NORTHERN WINDWARD ISLANDS ON FRIDAY, SPREADING INTO THE BRITISH AND
U.S. VIRGIN ISLANDS AND PUERTO RICO OVER THE WEEKEND. THIS RAINFALL
MAY PRODUCE ISOLATED FLASH AND URBAN FLOODING, ALONG WITH ISOLATED
MUDSLIDES IN AREAS OF HIGHER TERRAIN.
FORECAST POSITIONS AND MAX WINDS
INIT 19/2100Z 13.7N 56.6W 50 KT 60 MPH
12H 20/0600Z 14.2N 58.2W 50 KT 60 MPH
24H 20/1800Z 15.0N 59.9W 55 KT 65 MPH
36H 21/0600Z 16.4N 61.4W 60 KT 70 MPH
48H 21/1800Z 17.9N 62.4W 65 KT 75 MPH
60H 22/0600Z 19.5N 63.1W 70 KT 80 MPH
72H 22/1800Z 21.0N 63.3W 75 KT 85 MPH
96H 23/1800Z 24.3N 62.3W 75 KT 85 MPH
120H 24/1800Z 28.5N 57.5W 75 KT 85 MPH
FORECASTER BROWN
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