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Tropical Storm Rose Discussion Number   4
NWS National Hurricane Center Miami FL       AL172021
1100 PM AST Sun Sep 19 2021
 
The center of Rose has been very difficult to locate in infrared 
satellite imagery this evening. However, an earlier ASCAT-A overpass 
as well as an SSMIS microwave image from around of the time of the 
previous advisory were both helpful in establishing the initial 
position, motion, and intensity of the tropical cyclone.  Rose's 
center is located on the eastern edge of the main convective mass 
due to some southeasterly shear.  The ASCAT ambiguity data revealed 
an area of 30-35 kt winds around the southeastern portion of the 
circulation, so the wind speed remains 35 kt for this advisory.  
This is also in agreement with subjective Dvorak T-numbers of T2.5 
form both SAB and TAFB.
 
The ASCAT data indicated that Rose is located slightly west of the
earlier estimates, and the initial motion estimate is now
northwestward or 320/14 kt.  The cyclone is forecast to move
generally northwestward during the next several days around the
southwestern and western portions of a subtropical ridge located
over the far eastern Atlantic. After day 4, a strong mid- to
upper-level trough over the north-central Atlantic should cause
Rose to turn northward.  The dynamical models are in reasonably 
good agreement through about 60-72 hours, but there is growing
east-to-west (cross-track) spread after that time. The NHC track 
forecast is not too different from the previous advisory, and lies 
close to the various consensus models in deference to the 
increasing model spread late in the period.
 
Rose has about 24 hours over warm waters and in low vertical wind 
shear conditions in which to strengthen, and the new NHC intensity 
forecast for that time is unchanged from before. After 24 hours, 
increasing westerly shear is likely to result in some gradual 
weakening.  A further increase in shear is anticipated by day 3 as 
Rose approaches the aforementioned trough.  This is likely to result 
in additional weakening, and Rose is forecast to weaken to a 
tropical depression by day 4.  Some of the global model guidance 
suggests that weakening could occur faster than indicated below, and 
it is possible that Rose will degenerate into a remnant low by the 
end of the forecast period.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/0300Z 15.3N  31.1W   35 KT  40 MPH
 12H  20/1200Z 16.9N  32.6W   40 KT  45 MPH
 24H  21/0000Z 18.9N  34.2W   45 KT  50 MPH
 36H  21/1200Z 20.9N  35.5W   40 KT  45 MPH
 48H  22/0000Z 22.6N  36.6W   40 KT  45 MPH
 60H  22/1200Z 23.9N  37.5W   40 KT  45 MPH
 72H  23/0000Z 25.0N  38.7W   35 KT  40 MPH
 96H  24/0000Z 27.1N  40.8W   30 KT  35 MPH
120H  25/0000Z 29.0N  40.5W   30 KT  35 MPH
 
$$
Forecaster Brown
 
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