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Hurricane Sam Forecast Discussion


802 
WTNT43 KNHC 030238
TCDAT3

Hurricane Sam Discussion Number  42
NWS National Hurricane Center Miami FL       AL182021
1100 PM AST Sat Oct 02 2021

Sam continues to gradually weaken.  Conventional satellite imagery 
indicates that the eye has disappeared and that the cloud tops near 
the center are gradually warming.  Various objective and subjective 
satellite intensity estimates are in the 90-102 kt range, while 
scatterometer and experimental synthetic aperture radar data 
suggest lower winds than that.  The initial intensity is reduced to 
a possibly generous 100 kt.

The initial motion is northeastward or 040/14 kt.  A faster motion 
toward the northeast is expected during the next couple of days as 
Sam is steered by southwesterly flow between a deep-layer ridge to 
the east and a large mid- to upper-level low over Atlantic Canada. 
After Sam completes extratropical transition in about 48 h, a 
wobbly motion generally toward the northeast is expected as Sam 
interacts with one or more mid-latitude shortwave troughs.  The 
new forecast track is similar to the previous track and lies close 
to the various consensus models.

The hurricane is moving toward colder water, and it is approaching 
a frontal zone over the north Atlantic.  The cyclone should undergo 
extratropical transition during the next couple of days, and due to 
a favorable interaction with a mid-latitude trough it should weaken 
only slowly as it becomes a large and powerful extratropical low by 
48 h.  After that time, the baroclinic forcing ends and the low 
should gradually spin down over the far north Atlantic.  The new 
intensity forecast has only minor adjustments from the previous 
forecast.


Key Messages:

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  03/0300Z 36.4N  57.1W  100 KT 115 MPH
 12H  03/1200Z 37.7N  55.3W   95 KT 110 MPH
 24H  04/0000Z 39.7N  51.8W   90 KT 105 MPH
 36H  04/1200Z 42.7N  47.0W   85 KT 100 MPH
 48H  05/0000Z 47.3N  41.9W   80 KT  90 MPH...POST-TROP/EXTRATROP
 60H  05/1200Z 50.8N  39.5W   75 KT  85 MPH...POST-TROP/EXTRATROP
 72H  06/0000Z 51.7N  37.9W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  07/0000Z 54.0N  30.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  08/0000Z 60.5N  28.5W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven




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