[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 230911 CCA
TCDAT2

Tropical Storm Karen Discussion Number   5...Corrected
NWS National Hurricane Center Miami FL       AL122019
500 AM AST Mon Sep 23 2019

Corrected Key Messages

Karen's convective pattern has become quite disheveled looking this
morning due to 20-25 kt of northeasterly vertical wind shear. a
narrow band of deep convection has recently reformed in the
southeastern quadrant, but proximity to dry air has been hindering
development and organization of that convection. The initial
intensity has been held at 35 kt until the next reconnaissance
flight later this morning provides new information on the strength
of the cyclone. However, I would not be surprised if Karen has
weakened to a tropical depression based on the lack of significant
convection.

The initial motion is now 320/07 kt. The track guidance remains in
excellent agreement that Karen should continue a northwestward
motion today toward a break in the subtropical ridge, followed by a
northward motion on Tuesday that would take the center of the
cyclone near or over Puerto Rico and the U.S. Virgin Islands in
about 36 hours. Karen is forecast to emerge over the southwestern
Atlantic near 48 hours and then slow down significantly and possibly
even stall or loop several hundred nmi north of Puerto Rico on days
4 and 5 as a large ridge builds to the north of the cyclone. The new
NHC track forecast is similar to the previous advisory, and lies
close to the average of the consensus track models TVCN, NOAA-HCCA,
and FSSE.

The upper-level winds are expected to remain unfavorable for the
next 24 hours or so, and I would not be surprised if Karen weakens
to a tropical depression during that time. By 36 hours and beyond,
however, upper-level winds are expected to become much less hostile,
allowing some modest strengthening to occur. By days 4 and 5, Karen
is forecast to move underneath an upper-level anticyclone, which
should allow for more significant intensification to occur. The new
official intensity forecast is similar to the previous one, and
follows the trend of the various intensity consensus models.

Key Messages:

1.  Heavy rainfall will continue to affect portions of the southern
Windward Islands through tonight.

2.  Karen is forecast to approach Puerto Rico, and the U.S. and
British Virgin Islands on Tuesday, and a tropical storm warning is
in effect.  Tropical-storm-force winds, heavy rainfall, and flash
flooding are possible on these islands.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 13.6N  63.9W   35 KT  40 MPH
 12H  23/1800Z 14.5N  64.6W   35 KT  40 MPH
 24H  24/0600Z 16.1N  65.2W   35 KT  40 MPH
 36H  24/1800Z 18.0N  65.6W   35 KT  40 MPH
 48H  25/0600Z 20.1N  65.5W   40 KT  45 MPH
 72H  26/0600Z 24.6N  64.9W   45 KT  50 MPH
 96H  27/0600Z 26.5N  65.5W   50 KT  60 MPH
120H  28/0600Z 27.0N  67.0W   60 KT  70 MPH

$$
Forecaster Stewart
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