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Tropical Storm Rose Forecast Discussion


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485 
WTNT42 KNHC 192039
TCDAT2

Tropical Storm Rose Discussion Number   3
NWS National Hurricane Center Miami FL       AL172021
800 PM CVT Sun Sep 19 2021

Satellite images show that deep convection has increased in 
coverage near the low-level center during the last 6 hours, while 
the overall structure of the tropical cyclone has also improved. 
Based on the improved organization and consensus T-2.5 numbers from 
TAFB and SAB, the initial intensity is set to 35 kt, making Rose 
the seventeenth named storm of the busy 2021 Atlantic hurricane 
season.  Only 2005 and 2020 have had the seventeenth named storm on 
an earlier date.

The 12-hour motion is north-northwest, or 330/14.  However, Rose 
appears to be moving more in a northwest direction during the past 
few hours.  This is probably the start of a northwest motion 
that should continue through day 4 as the system moves along the 
southwestern and western periphery of a subtropical ridge that 
extends from Africa across the Cabo Verde Islands.  A turn to the 
north is predicted in about 5 days, as Rose comes under the 
influence of a strong mid-level trough approaching from the 
northwest.  No significant changes were made to the previous track 
forecast.

Environmental conditions are conducive for strengthening during the
next day or so, with low wind shear, SSTs near 27C, and sufficient 
mid-level atmospheric moisture.  Therefore, a little more 
strengthening is shown compared to the previous NHC forecast.  The 
new NHC forecast is in agreement with the various consensus aids, 
but slightly below the SHIPS model, in deference to the global 
models which show a weaker cyclone.  Westerly wind shear will 
likely increase in about 36 hours as a strong upper-level trough 
approaches from the northwest.  Given that the cyclone is forecast
to remain rather small, it will likely be vulnerable to the higher 
shear so weakening is forecast in the 36-72 h time period.  Beyond 
day 3, a further increase in wind shear is expected to cause Rose to 
weaken to a tropical depression.  Although not explicitly forecast, 
it is possible that the cyclone could become a remnant low in 4-5 
days if the shear is too much for the system to handle.


FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 14.3N  29.9W   35 KT  40 MPH
 12H  20/0600Z 15.9N  31.4W   40 KT  45 MPH
 24H  20/1800Z 17.9N  33.3W   45 KT  50 MPH
 36H  21/0600Z 20.0N  34.8W   45 KT  50 MPH
 48H  21/1800Z 22.0N  36.0W   40 KT  45 MPH
 60H  22/0600Z 23.5N  37.0W   40 KT  45 MPH
 72H  22/1800Z 24.7N  38.0W   35 KT  40 MPH
 96H  23/1800Z 26.7N  40.6W   30 KT  35 MPH
120H  24/1800Z 28.7N  41.2W   30 KT  35 MPH

$$
Forecaster Hagen/Blake