730
WTNT45 KNHC 222035
TCDAT5
HURRICANE TAMMY DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL202023
500 PM AST SUN OCT 22 2023
THE CORE OF TAMMY CONTINUES TO PULL AWAY FROM THE NORTHERN LEEWARD
ISLANDS, BUT A TRAILING AREA OF HEAVY RAIN CONTINUES TO AFFECT
PORTIONS OF THE WINDWARD AND LEEWARD ISLANDS. THE NOAA HURRICANE
HUNTERS FOUND MAXIMUM 750-MB FLIGHT-LEVEL WINDS OF 83 KT AND PEAK
SFMR WINDS OF AROUND 70 KT. IN ADDITION, THE MINIMUM PRESSURE HAS
FALLEN TO 988 MB. THESE DATA SUPPORT NUDGING THE INITIAL INTENSITY
UP TO 75 KT. TAMMY CONTINUES TO HAVE A SMALL CENTRAL DENSE
OVERCAST PATTERN IN SATELLITE IMAGES WITH VERY COLD CLOUD TOPS
EVIDENT NEAR THE CENTER. AN ASCAT-B PASS FROM A FEW HOURS AGO WAS
HELPFUL IN ADJUSTING THE 34- AND 50-KT WIND RADII, AND IT CONFIRMED
THAT TAMMY REMAINS A RELATIVELY COMPACT TROPICAL CYCLONE.
THE HURRICANE IS MOVING NORTHWESTWARD AT 8 KT ON THE SOUTHWESTERN
PERIPHERY OF A SUBTROPICAL RIDGE CENTERED OVER THE CENTRAL ATLANTIC.
A TURN TO THE NORTH IS FORECAST TO OCCUR LATE TONIGHT, FOLLOWED BY A
NORTHEASTWARD MOTION BEGINNING MONDAY NIGHT WHEN A LARGE-SCALE
TROUGH OVER THE NORTHEAST U.S. SHIFTS EASTWARD, ERODING THE RIDGE.
AFTER THAT TIME, THE MODELS SHOW THE TROUGH CUTTING OFF AND MERGING
WITH TAMMY, WHICH WILL LIKELY CAUSE A SHARP TURN TO THE LEFT. THE
MODELS HAVE COME IN SLIGHTLY BETTER AGREEMENT IN THE OVERALL
SCENARIO, AND ONLY SMALL CHANGES WERE MADE TO THE PREVIOUS NHC TRACK
FORECAST.
TAMMY WILL LIKELY FLUCTUATE IN STRENGTH DURING THE NEXT FEW DAYS
WHILE IT REMAINS OVER WARM SSTS AND IN A MODERATE WIND SHEAR
ENVIRONMENT. AFTER TAMMY MERGES WITH THE TROUGH, DRY AIR
ENTRAINMENT AND STRONGER SHEAR SHOULD CAUSE WEAKENING AND LIKELY
LEAD TO EXTRATROPICAL TRANSITION IN 3 TO 4 DAYS. THE NHC INTENSITY
FORECAST IS SIMILAR TO THE PREVIOUS ONE AND ROUGHLY IN THE MIDDLE
OF THE GUIDANCE ENVELOPE.
KEY MESSAGES:
1. THE HEAVIEST RAINS FROM TAMMY WILL CONTINUE OVER THE LEEWARD
ISLANDS THROUGH TONIGHT. THIS RAINFALL MAY PRODUCE ISOLATED FLASH
AND URBAN FLOODING, ALONG WITH ISOLATED MUDSLIDES IN AREAS OF HIGHER
TERRAIN.
FORECAST POSITIONS AND MAX WINDS
INIT 22/2100Z 19.9N 63.4W 75 KT 85 MPH
12H 23/0600Z 20.9N 63.8W 75 KT 85 MPH
24H 23/1800Z 22.0N 63.6W 80 KT 90 MPH
36H 24/0600Z 22.8N 62.9W 80 KT 90 MPH
48H 24/1800Z 23.6N 62.0W 80 KT 90 MPH
60H 25/0600Z 24.4N 61.0W 80 KT 90 MPH
72H 25/1800Z 25.8N 60.2W 75 KT 85 MPH
96H 26/1800Z 28.9N 60.4W 60 KT 70 MPH...POST-TROP/EXTRATROP
120H 27/1800Z 30.7N 64.3W 50 KT 60 MPH...POST-TROP/EXTRATROP
FORECASTER CANGIALOSI
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