Atlantic Basin Tropical Cyclones

Hurricane Sam Forecast Discussion


000
WTNT43 KNHC 020241
TCDAT3

Hurricane Sam Discussion Number  38
NWS National Hurricane Center Miami FL       AL182021
1100 PM AST Fri Oct 01 2021

The satellite appearance of Sam has degraded slightly during the 
past few hours, with the eye becoming more cloud filled and the 
eyewall cloud tops become a little less symmetric.  Various 
subjective and objective satellite intensity estimates are in the 
115-130 kt range, and based on the slight decay the initial 
intensity is lowered to 125 kt.  An Air Force Reserve Hurricane 
Hunter aircraft is currently enroute to investigate Sam.

Sam is making its forecast turn toward the north-northeast with the 
initial motion now 020/15 kt.  There is no change to the track 
forecast philosophy and little change to the forecast track from the 
previous advisory.  The steering flow between a deep-layer ridge to 
the northeast and east of Sam and a large mid-latitude low pressure 
system centered over Atlantic Canada should cause Sam to turn 
northeastward during the next 24 h, followed by a continued 
northeastward motion as the system become entrained in southwesterly 
mid-latitude flow.  The models are in fairly good agreement, 
although there is some spread in both the track and the speed due to 
model differences in the cyclone's evolution as it becomes 
extratropical.  The new forecast track lies close to the center of 
the guidance envelope and the various consensus models.

Slow weakening is expected to continue during the next 2-3 days as 
Sam moves over cooler sea surface temperatures and begins 
extratropical transition.  This is likely to be complete by 72 h, 
with the global models suggesting that Sam will evolve into a 
warm-core seclusion extratropical low.  Based on this and the 
guidance, it is likely that the cyclone will maintain hurricane 
strength until after the transition is done.  By the end of the 
forecast period, the extratropical low is expected to be decaying 
over the far north Atlantic.  The new intensity forecast lies at the 
upper edge of the intensity guidance.


Key Messages:

1. Swells generated by Sam will impact the northern Leeward Islands
the Greater Antilles, the Bahamas, and Bermuda during the next
couple of days.  Swells are expected to reach the United States
east coast and Atlantic Canada on Saturday.  These swells could
cause life-threatening surf and rip current conditions.  Please
consult products from your local weather office.

2. Tropical storm conditions are possible on Bermuda during the 
next several hours, and a Tropical Storm Warning is in effect for 
the island.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 31.4N  61.2W  125 KT 145 MPH
 12H  02/1200Z 33.5N  60.2W  120 KT 140 MPH
 24H  03/0000Z 35.8N  58.3W  110 KT 125 MPH
 36H  03/1200Z 37.7N  55.6W  100 KT 115 MPH
 48H  04/0000Z 39.6N  52.2W   95 KT 110 MPH
 60H  04/1200Z 43.0N  47.3W   90 KT 105 MPH
 72H  05/0000Z 47.2N  43.2W   80 KT  90 MPH...POST-TROP/EXTRATROP
 96H  06/0000Z 50.5N  38.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
120H  07/0000Z 54.5N  27.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven



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