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Hurricane Sam Discussion Number 46
NWS National Hurricane Center Miami FL AL182021
1100 PM AST Sun Oct 03 2021
Sam still had a surprise up its sleeve tonight, with its eye
becoming warmer on satellite images along with a stronger eyewall.
Microwave data from earlier today indicated that Sam has been
undergoing a concentric eyewall cycle, and it appears that the inner
eyewall has become better defined. Regardless, it is not every day
you see a hurricane with that clear of an eye near 40N, and the
intensity estimates the evening range from 90-100 kt. Given the
concentric eyewalls, the initial wind speed is conservatively
raised to 90 kt, but it could be higher.
High-resolution NOAA OISST data indicate that Sam is moving near a
warm eddy along the north wall of the Gulf Stream. This favorable
factor, in addition to low shear, should keep Sam's weakening to a
minimum in the near term. Later on, although the shear increases
rapidly and SSTs fall quickly, Sam is expected to transition into a
powerful extratropical cyclone late Monday or early Tuesday due to a
mid-latitude trough interaction well east of Newfoundland. This
should cause extratropical Sam to maintain hurricane-force winds
until early Wednesday. A slow weakening is expected thereafter as
it slowly spins down as an occluded low. No significant changes
were made to the previous forecast.
Sam is moving faster, now 050/17 kt. A northeastward motion and
continued acceleration is forecast through Monday as the cyclone
gets caught in southwesterly flow ahead of the mid-latitude trough.
The tropical cyclone is expected to be the main surface low center
as it merges with the trough in a couple days, hooking briefly to
the left. Thereafter, the system should resume a northeastward
motion and gradually turn northward and even westward at long range
as it moves around another trough. Model guidance is close to the
previous cycle, even with the loopy track, and the new NHC forecast
is basically just an update of the last advisory.
1. Swells generated by Sam will impact the northern Leeward Islands,
the Greater Antilles, the Bahamas, Bermuda, the eastern United
States and Atlantic Canada for the next couple of days. These
swells could cause life-threatening surf and rip current conditions.
Please consult products from your local weather office.
FORECAST POSITIONS AND MAX WINDS
INIT 04/0300Z 39.3N 51.2W 90 KT 105 MPH
12H 04/1200Z 41.6N 47.3W 85 KT 100 MPH
24H 05/0000Z 46.5N 42.1W 75 KT 85 MPH
36H 05/1200Z 50.4N 40.3W 70 KT 80 MPH...POST-TROP/EXTRATROP
48H 06/0000Z 50.8N 38.3W 65 KT 75 MPH...POST-TROP/EXTRATROP
60H 06/1200Z 51.6N 33.3W 55 KT 65 MPH...POST-TROP/EXTRATROP
72H 07/0000Z 54.5N 28.2W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 08/0000Z 61.0N 28.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 09/0000Z 61.5N 32.0W 40 KT 45 MPH...POST-TROP/EXTRATROP