Issued at 1100 AM AST Sat Oct 02 2021

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Hurricane Sam Discussion Number 40
NWS National Hurricane Center Miami FL

AL182021
1100 AM AST Sat Oct 02 2021

Sam has been an impressive hurricane during the past several days.

The latest satellite imagery shows it remains a powerful system,
with a well-defined eye and symmetric cloud pattern. In fact,
since the plane left overnight, the eye has actually warmed, with
little change in the eyewall convection. Thus the initial intensity
will stay 115 kt, above the latest satellite classifications, but
consistent with the earlier aircraft data and low bias of the
Dvorak technique for much of the this storm. Sam is now in the top
10 for consecutive days as a category 4 hurricane or greater in
the historical record, about the same as Matthew 2016.

The hurricane is forecast to gradually lose strength during the
next 36 hours or so while it remains over marginally warm waters,
but in fairly light shear. In fact, some of the guidance decrease
the shear overnight, which should allow Sam to keep much of its
strength, provided it doesn't undertake an eyewall cycle. The new
intensity forecast is higher in the first day or so, consistent
with the latest model solutions. In about 2 days, Sam will cross
the north wall of the Gulf Stream, and in 3 days is expected to
spectacularly transition into a large hurricane-force post-tropical
cyclone over the far north Atlantic. No changes were made to the
end of the intensity forecast.

Sam has turned northeastward at about 15 kt. The hurricane should
accelerate later this weekend due to increasing flow between a
deep-layer ridge to the east and a large mid- to upper-level low
over Atlantic Canada. By midweek the system is forecast to turn
more to the north-northeast as it becomes a spoke in a very large
extratropical low over the far North Atlantic. The new forecast has
shifted somewhat eastward during the first couple of days but ends
up very near the last advisory by day 5.

Key Messages:

1. Swells generated by Sam will impact the northern Leeward Islands,
the Greater Antilles, the Bahamas, Bermuda, the eastern United
States coast 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 02/1500Z 33.9N 59.3W 115 KT 130 MPH
12H 03/0000Z 35.6N 57.8W 105 KT 120 MPH
24H 03/1200Z 37.4N 55.3W 100 KT 115 MPH
36H 04/0000Z 39.2N 52.0W

95 KT 110 MPH
48H 04/1200Z 41.8N 47.3W

85 KT 100 MPH
60H 05/0000Z 46.0N 42.0W

80 KT 90 MPH
72H 05/1200Z 50.0N 38.5W

75 KT 85 MPH...POST-TROP/EXTRATROP
96H 06/1200Z 53.0N 33.0W

55 KT 65 MPH...POST-TROP/EXTRATROP
120H 07/1200Z 59.0N 26.0W

45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Blake

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