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Hurricane Sam Discussion Number 32
NWS National Hurricane Center Miami FL AL182021
1100 AM AST Thu Sep 30 2021
Sam continues to look quite impressive on satellite images, with a
20-25 n mi wide eye surrounded by very deep convection. The
system's convective banding features and upper-level anticyclonic
outflow also remain well-defined, with particularly strong outflow
to the northwest and north. Subjective and objective Dvorak
intensity estimates have not changed significantly since earlier
this morning, so the advisory intensity will remain at 125 kt.
Interestingly, aircraft observations show that Sam has been a
little stronger than indicated by satellite-derived intensity
estimates, which underscores the value of aerial reconnaissance
of tropical cyclones. Another Air Force Hurricane Hunter aircraft
is scheduled to investigate the hurricane later today.
Sam should continue to move over waters of high oceanic heat
content and within a low-shear atmospheric environment for the next
24 hours or so. Thus, it could still strengthen a little today and
tonight. By 48 hours, decreasing SSTs and increasing shear should
lead to a gradual weakening trend. Around day 5, global model
fields suggest that Sam will be merging with a baroclinic zone and
transition into a large and powerful extratropical cyclone over the
north Atlantic. The official intensity forecast is in good
agreement with the HCCA corrected consensus model prediction.
The hurricane is moving a little faster toward the northwest, or at
about 320/11 kt. During the next couple of days, a gradual turn
toward the north is likely as Sam rounds the western end of a large
subtropical anticyclone over the eastern and central Atlantic.
Thereafter, Sam is forecast to move generally northeastward in the
flow between the anticyclone and a trough near Atlantic Canada.
The NHC forecast is very similar to a consensus of the typically
reliable GFS and ECMWF predictions, with a little bit of smoothing
around days 3-4.
Although the core of Sam is forecast to pass east of Bermuda early
Saturday, the tropical-storm-force wind field is forecast to expand
and could pass very close to the island beginning late Friday night
or early Saturday. Therefore, a Tropical Storm Watch is in effect
1. Swells generated by Sam will impact the Northern Leeward Islands
and the Greater Antilles, including Puerto Rico, during the next
few days. Swells are expected to reach Bermuda and the Bahamas by
Friday, and then spread to the United States east coast by this
weekend. These swells could cause life-threatening surf and rip
current conditions. Please consult products from your local
2. Tropical storm conditions are possible on Bermuda beginning
Friday night or early Saturday, and a Tropical Storm Watch has
been issued for that island.
FORECAST POSITIONS AND MAX WINDS
INIT 30/1500Z 22.6N 60.0W 125 KT 145 MPH
12H 01/0000Z 24.4N 60.8W 130 KT 150 MPH
24H 01/1200Z 27.2N 61.7W 125 KT 145 MPH
36H 02/0000Z 30.2N 61.6W 115 KT 130 MPH
48H 02/1200Z 32.7N 60.8W 105 KT 120 MPH
60H 03/0000Z 34.9N 59.2W 95 KT 110 MPH
72H 03/1200Z 36.9N 57.0W 90 KT 105 MPH
96H 04/1200Z 40.0N 51.0W 80 KT 90 MPH
120H 05/1200Z 44.5N 45.5W 65 KT 75 MPH...POST-TROP/EXTRATROP