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Tropical Storm Rose Forecast Discussion

WTNT42 KNHC 202033

Tropical Storm Rose Discussion Number   7
NWS National Hurricane Center Miami FL       AL172021
500 PM AST Mon Sep 20 2021

Satellite images show that Rose hasn't changed much during the past 
several hours, with the center on the northern side of the cloud 
shield.  The last microwave pass from a few hours ago showed that 
the mid- and low-level centers of the cyclone remained 60-90 n mi 
apart, which is probably a sign that it isn't strengthening.  The 
initial wind speed remains 35 kt based on continuity, and hopefully 
scatterometer data will be available for the next advisory due to 
the recent high bias of the conventional satellite estimates.

The window for strengthening of the tropical cyclone is closing soon 
due to increasing shear and likely intrusions of dry mid-level air. 
These factors should cause the storm to start a weakening trend 
sometime tomorrow.  The long-term future of Rose doesn't look golden 
either due to further increasing shear from an incoming upper- level 
trough.  The new forecast is just a shade lower than the previous 
one, near the model consensus, with Rose likely sinking to a 
depression in a few days and degenerating to a remnant low by day 5.

The initial motion remains northwestward at about 14 kt.  Rose is
is likely to continue moving in that general direction during 
the next couple of days around the southwestern and western 
periphery of a strong subtropical ridge.  Beyond that time, 
guidance is coming into good agreement on a mid- to upper-level 
trough over the north-central Atlantic causing the cyclone to 
recurve to the north, northeast and even east-northeastward by 
the weekend.  While the models don't agree on how sharp of a 
turn will occur, they are at least consistent that this trough 
will take the storm into a hostile environment and decay. The new 
forecast is again adjusted well to northeast at long range, and 
still might not be far enough to the east.


INIT  20/2100Z 18.4N  34.4W   35 KT  40 MPH
 12H  21/0600Z 20.0N  35.6W   40 KT  45 MPH
 24H  21/1800Z 21.8N  36.7W   35 KT  40 MPH
 36H  22/0600Z 23.3N  37.8W   35 KT  40 MPH
 48H  22/1800Z 24.5N  38.9W   30 KT  35 MPH
 60H  23/0600Z 26.0N  39.9W   30 KT  35 MPH
 72H  23/1800Z 27.3N  40.2W   30 KT  35 MPH
 96H  24/1800Z 29.2N  38.8W   25 KT  30 MPH
120H  25/1800Z 31.5N  34.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

Forecaster Blake

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