[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 231441
TCDAT2

Tropical Storm Karen Discussion Number   6
NWS National Hurricane Center Miami FL       AL122019
1100 AM AST Mon Sep 23 2019

Although deep convection has recently developed near the low-level
swirl seen in early morning visible satellite imagery, the Air Force
Reserve reconnaissance aircraft that has been investigating Karen
has had difficultly finding a closed surface circulation.  It is
possible that a center reformation will occur near the new
convection, so the system is still being classified as a tropical
cyclone for now.  The aircraft has found believable SFMR winds of
30-35 kt over the eastern portion of the system, which still
supports an initial intensity of 35 kt.  Given the current structure
of Karen and moderate to strong northeasterly shear that should
remain over the storm for the next 24 hours, no change in strength
is anticipated during that time.  It is also possible that Karen
could degenerate into an open wave, if it has not done so already.
Regardless of whether or not Karen is a tropical cyclone when it
passes near Puerto Rico and the Virgin Islands, the system is likely
to produce tropical-storm-force winds in squalls and heavy rainfall
over those areas.  After that time, upper-level winds are forecast
to become more conducive for intensification, and the NHC forecast
calls for gradual strengthening like most of the typically reliable
intensity guidance, however, the confidence in this portion of the
intensity forecast is low.

The initial motion estimate is 335/10 kt.  Despite the overall lack
of organization of the system, the track guidance is still in good
agreement on Karen turning northward tonight or early Tuesday into
a weakness in the ridge over the western Atlantic caused by
Tropical Storm Jerry to its north.  After 72 hours, a deep-layer
ridge is forecast to build over the southeastern United States and
western Atlantic which should slow Karen's northward progress and
could cause the system to essentially stall over the western
Atlantic by the end of the period.  The new NHC track forecast is
again close to the previous advisory, and is near the consensus
aids through 96 h.  At 120 h, the NHC forecast is south of the
consensus models in deference to the more equatorward position
shown by the ECMWF, but the spread of the guidance by that time
is quite large, and confidence in the track forecast at days 4
and 5 is quite low.

Key Messages:

1.  Regardless of Karen's status as a tropical cyclone, this system
is expected to bring tropical-storm-force winds, heavy rainfall,
flash floods and mudslides to Puerto Rico and the U.S. and British
Virgin Islands on Tuesday, where a tropical storm warning is
in effect.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 14.9N  64.8W   35 KT  40 MPH
 12H  24/0000Z 16.0N  65.3W   35 KT  40 MPH
 24H  24/1200Z 17.7N  65.8W   35 KT  40 MPH
 36H  25/0000Z 19.6N  65.9W   35 KT  40 MPH
 48H  25/1200Z 21.9N  65.7W   40 KT  45 MPH
 72H  26/1200Z 25.6N  65.3W   45 KT  50 MPH
 96H  27/1200Z 27.0N  65.8W   50 KT  60 MPH
120H  28/1200Z 27.0N  67.0W   60 KT  70 MPH

$$
Forecaster Brown
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