[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 212036
TCDAT2

Tropical Storm Rose Discussion Number  11
NWS National Hurricane Center Miami FL       AL172021
500 PM AST Tue Sep 21 2021

Shear continues to disrupt Rose's deep convection, with only a
small cluster remaining in the eastern quadrant of the storm.
Dvorak estimates support holding the intensity at 35 kt for one
more advisory, and hopefully the evening scatterometer passes will
get a good look at the cyclone's wind field.

Rose is moving more slowly to the northwest, now about 10 kt.  The
storm should gradually turn northward during the next couple of
days around the southwestern side of a subtropical ridge. Somewhat
surprisingly, guidance has shifted westward during this time,
perhaps due to a weaker Rose not feeling as much of the
southwesterly flow aloft.  This westward shift in the track also
puts Rose in a position to either get shunted east like the ECMWF
solution, or uprooted more to the northeast at long range similar to
the GFS.  Given the recent and large model changes since the last
cycle, this forecast conservatively moves westward toward the model
mean at most time ranges, not too far from a 50/50 blend of the
GFS/ECMWF models (GFEX).

The cyclone has a difficult environment ahead, with persistent
moderate westerly or northwesterly shear, plentiful dry air aloft
and only marginally warm waters.  All of the guidance shows Rose
decaying into a tropical depression fairly soon, and it could even
wither into a remnant low tomorrow or Thursday in the harsh
conditions.  However, the shear could let up just enough, along with
some upper divergence from an upcoming trough interaction, to
continue to produce deep convection for a few days.  This isn't an
easy forecast because some of the guidance actually re-intensifies
Rose due to the trough, while other guidance completely dissipates
the tropical cyclone.  Given the considerable uncertainty, I've kept
the previous forecast the same at long range until more clarity
emerges in the model suite.


FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 22.5N  37.7W   35 KT  40 MPH
 12H  22/0600Z 23.5N  38.6W   30 KT  35 MPH
 24H  22/1800Z 24.8N  39.8W   30 KT  35 MPH
 36H  23/0600Z 26.2N  40.8W   30 KT  35 MPH
 48H  23/1800Z 27.5N  41.3W   30 KT  35 MPH
 60H  24/0600Z 28.8N  40.7W   30 KT  35 MPH
 72H  24/1800Z 29.8N  38.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  25/1800Z 31.5N  33.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  26/1800Z...DISSIPATED

$$
Forecaster Blake
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