115
WTNT45 KNHC 220259
TCDAT5
HURRICANE TAMMY DISCUSSION NUMBER 15
NWS NATIONAL HURRICANE CENTER MIAMI FL AL202023
1100 PM AST SAT OCT 21 2023
AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT DATA, ALONG WITH RADAR
IMAGERY FROM GUADELOUPE, INDICATE THAT THE CENTER OF TAMMY PASSED
OVER THE ISLAND OF BARBUDA A COUPLE OF HOURS AGO. THE HURRICANE
CONTINUES TO PRODUCE INTENSE CONVECTION IN A SMALL CDO FEATURE WITH
SOME ILL-DEFINED BANDS NORTH AND NORTHEAST OF THE CENTER. THE
EYEWALL HAS GENERALLY NOT BEEN CLOSED ON THE RADAR IMAGES. THERE
ARE STILL SOME AREAS OF STRONG CONVECTION AFFECTING PORTIONS OF THE
LESSER ANTILLES TO THE SOUTH OF TAMMY. FLIGHT-LEVEL AND SFMR WINDS
ALONG WITH DOPPLER VELOCITY DATA SUGGESTED THAT THE MAXIMUM WINDS
HAD DECREASED SLIGHTLY, BUT THERE WAS AN UNOFFICIAL REPORT OF A
SUSTAINED WIND OF 78 KT FROM BARBUDA. BASED ON A BLEND OF THE
AIRCRAFT DATA AND THE BARBUDA OBSERVATION, THE INTENSITY IS HELD AT
75 KT FOR THIS ADVISORY.
CENTER FIXES INDICATE THAT THE HURRICANE CONTINUES ON ITS
NORTH-NORTHWESTWARD TREK WITH AN ESTIMATED MOTION OF 330/9 KT. OVER
THE NEXT COUPLE OF DAYS, TAMMY SHOULD TURN NORTHWARD WHILE IT MOVES
ALONG THE WESTERN SIDE OF A LARGE SUBTROPICAL HIGH. THEN, THE
SYSTEM SHOULD TURN, AT LEAST TEMPORARILY, NORTHEASTWARD ON THE
SOUTHEASTERN PERIPHERY OF A MID-TROPOSPHERIC TROUGH OVER THE WESTERN
ATLANTIC. BEGINNING AROUND 3 DAYS, THE TRACK FORECAST BECOMES
CHALLENGING, SINCE THE GLOBAL MODELS INDICATE THAT THE WESTERN
ATLANTIC TROUGH WILL BYPASS TAMMY AFTER 72 HOURS WHILE IT CONTINUES
EASTWARD. A RIDGE COULD THEN BUILD IN TO THE NORTHWEST OF THE
SYSTEM AND CAUSE IT TO TURN TO THE LEFT. AS NOTED EARLIER, THERE IS
A VERY LARGE SPREAD IN THE TRACK GUIDANCE IN THE LATTER PART OF THE
FORECAST PERIOD. THERE IS LOW CONFIDENCE IN THE 4- AND 5-DAY NHC
FORECAST POSITIONS.
TAMMY SHOULD REMAIN OVER VERY WARM WATERS WITH MODERATE VERTICAL
WIND SHEAR FOR THE NEXT COUPLE OF DAYS. SO, SOME SLIGHT
STRENGTHENING IS STILL FORECAST. BY 60 OR 72 HOURS, INCREASING
SHEAR IS LIKELY TO INDUCE A WEAKENING TREND. THE OFFICIAL INTENSITY
FORECAST IS SIMILAR TO THE LATEST DECAY-SHIPS GUIDANCE.
KEY MESSAGES:
1. HURRICANE AND TROPICAL STORM CONDITIONS ARE EXPECTED IN PORTIONS
OF THE NORTHERN LEEWARD ISLANDS THROUGH EARLY SUNDAY.
2. THE HEAVIEST RAINS FROM TAMMY WILL CONTINUE OVER THE LEEWARD
ISLANDS THROUGH SUNDAY. THIS RAINFALL MAY PRODUCE ISOLATED FLASH AND
URBAN FLOODING, ALONG WITH ISOLATED MUDSLIDES IN AREAS OF HIGHER
TERRAIN.
3. A STORM SURGE COULD PRODUCE COASTAL FLOODING IN AREAS OF ONSHORE
WINDS AS THE CENTER OF TAMMY MOVES NEAR OR OVER THE LEEWARD ISLANDS.
NEAR THE COAST, THE SURGE WILL BE ACCOMPANIED BY LARGE AND DANGEROUS
WAVES.
FORECAST POSITIONS AND MAX WINDS
INIT 22/0300Z 17.8N 61.9W 75 KT 85 MPH
12H 22/1200Z 18.8N 62.5W 75 KT 85 MPH
24H 23/0000Z 20.2N 63.4W 80 KT 90 MPH
36H 23/1200Z 21.5N 63.9W 80 KT 90 MPH
48H 24/0000Z 22.6N 63.8W 80 KT 90 MPH
60H 24/1200Z 23.1N 63.6W 80 KT 90 MPH
72H 25/0000Z 23.5N 63.0W 75 KT 85 MPH
96H 26/0000Z 25.0N 62.5W 70 KT 80 MPH
120H 27/0000Z 27.5N 63.5W 60 KT 70 MPH
FORECASTER PASCH
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