Atlantic Basin Tropical Cyclones

Tropical Storm Rose Forecast Discussion


898 
WTNT42 KNHC 210245
TCDAT2

Tropical Storm Rose Discussion Number   8
NWS National Hurricane Center Miami FL       AL172021
1100 PM AST Mon Sep 20 2021

Although Rose's convective pattern does not appear to be as 
organized as it was earlier today, a couple of ASCAT overpasses this 
evening indicated that the tropical cyclone has strengthened since 
this morning. Both ASCAT-A and -B instruments detected 40-45 kt 
winds around the southeastern portion of the circulation, and the 
initial intensity was raised to 45 kt around 0000 UTC with the 
issuance of a Tropical Cyclone Update.  That intensity is maintained 
for this advisory, and it is also in agreement with subjective 
Dvorak data T-numbers of 3.0 from TAFB and SAB. 

The ASCAT data also indicated that the center of Rose is located to 
the west of the previous estimates, near the northwestern edge of 
the convective mass noted in satellite imagery.  As a result of the 
center re-location, the initial motion is a somewhat uncertain 
320/13 kt.  Although the short-term portion of the track forecast 
has been adjusted westward due to the more westward initial 
position, there has been no overall change in forecast track 
reasoning for this advisory.  Rose should continue northwestward 
around the western portion of a strong subtropical ridge during the 
next couple of days.  Beyond that time, a mid- to upper-level trough 
over the north-central Atlantic should cause Rose to recurve 
northward, then northeastward, and finally east-northeastward by the 
end of the forecast period.  The dynamical models are in general  
agreement on this scenario but there are some differences in how 
sharp Rose will turn, and how fast it will move northeastward late 
in the period.  The new NHC track forecast shows a somewhat sharper 
turn than the previous advisory to be closer to the latest consensus 
aids. 

Rose has likely reached its peak intensity as increasing shear and 
the entrainment of drier mid-level air are likely to cause weakening 
by this time tomorrow. Additional weakening is expected after that 
time as a further increase in shear is anticipated when Rose nears 
the aforementioned trough in 2 to 3 days. The updated NHC wind speed 
forecast is slightly stronger at 12 and 24 hours due to the higher 
initial intensity, but is unchanged after that time. Given the 
expected hostile environmental conditions, it would not be 
surprising to see Rose wither more quickly and degenerate into a 
remnant low sooner than indicated below.  That is indicated by at 
least some of the global model guidance. 

FORECAST POSITIONS AND MAX WINDS

INIT  21/0300Z 18.9N  35.4W   45 KT  50 MPH
 12H  21/1200Z 20.5N  36.5W   45 KT  50 MPH
 24H  22/0000Z 22.2N  37.6W   40 KT  45 MPH
 36H  22/1200Z 23.5N  38.7W   35 KT  40 MPH
 48H  23/0000Z 24.8N  39.9W   30 KT  35 MPH
 60H  23/1200Z 26.1N  40.7W   30 KT  35 MPH
 72H  24/0000Z 27.3N  40.8W   30 KT  35 MPH
 96H  25/0000Z 29.0N  38.2W   25 KT  30 MPH
120H  26/0000Z 30.5N  33.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown




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