NWS National Hurricane Center Miami FL AL182021
1100 AM AST Sun Sep 26 2021

...SAM CONTINUES MOVING SLOWLY WEST-NORTHWESTWARD AS A CATEGORY 4
HURRICANE...

Sam is moving toward the west-northwest, or 290/7 kt. A deep-layer
subtropical ridge to the north and northeast of Sam should generally
steer the hurricane west-northwestward to northwestward for the next
several days. By midweek, an amplifying upper-level trough will
move off the east coast of the U.S. and dig southward over the
western Atlantic, which will erode the western extent of the
steering ridge. The deep-layer southerly flow ahead of the trough
should cause Sam to begin recurving, with a somewhat faster
north-northwestward motion forecast by day 5. The latest NHC track
forecast was adjusted a little to the left, or southwest of the
previous official forecast, mainly at days 4 and 5, but not quite as
far southwest as the model consensus aids.

The hurricane will likely experience some fluctuations in intensity
during the next few days. Guidance, however, indicates that the
chance of an eyewall replacement cycle during the next 36 hours is
below climatology. Sam will remain over warm sea-surface
temperatures and in a low wind shear environment for the next 3
days, with less than 10 kt of shear diagnosed by the SHIPS guidance.
It is possible that Sam's slow forward motion during the next 2 to 3
days could cause some upwelling of cooler water, but this will
probably not result in significant weakening. The official NHC
intensity forecast lies on the high end of the guidance for the
first 36-48 h of the forecast period. Thereafter, the NHC forecast
is closer to the middle of the guidance envelope. Some gradual
weakening is forecast later in the period as southwesterly vertical
wind shear begins to increase, but Sam is still forecast to remain a
major hurricane through the 5-day period.

The radii were expanded slightly by 5-10 n mi in the western
semicircle from the previous advisory based on a 1155 UTC ASCAT-A
pass.


FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 13.9N 50.2W 125 KT 145 MPH
12H 27/0000Z 14.4N 51.2W 125 KT 145 MPH
24H 27/1200Z 15.2N 52.4W 120 KT 140 MPH
36H 28/0000Z 16.0N 53.5W 120 KT 140 MPH
48H 28/1200Z 16.8N 54.6W 115 KT 130 MPH
60H 29/0000Z 17.7N 55.7W 115 KT 130 MPH
72H 29/1200Z 18.6N 57.1W 115 KT 130 MPH
96H 30/1200Z 21.4N 60.3W 110 KT 125 MPH
120H 01/1200Z 25.6N 63.1W 110 KT 125 MPH