[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 230254
TCDAT2

Tropical Storm Karen Discussion Number   4
NWS National Hurricane Center Miami FL       AL122019
1100 PM AST Sun Sep 22 2019

Karen remains poorly organized this evening, with the low-level
center exposed to the north of the main convective mass due to the
effects of 15-20 kt of northeasterly vertical shear.  The initial
intensity will be held at 35 kt based on earlier Air Force Reserve
Hurricane Hunter data that included maximum 1500 ft flight-level
winds of 42 kt and SFMR surface wind estimates near 35 kt.

The initial motion is 295/10.  The track guidance is in excellent
agreement that Karen should turn northwestward during the next 6-12
h in response to a break in a ridge to the north of the storm,
followed by a northward motion that would take the center near
Puerto Rico and the Virgin Islands into the Atlantic between 36-48
h.  Late in the forecast period, the steering currents are expected
to weaken as a strong deep-layer ridge builds eastward from the
United States into the western Atlantic.  This should cause Karen
to slow its forward motion.  The new forecast track is little
changed from the previous track and is near the center of the
guidance envelope and the various consensus models.

The upper-level winds are currently not favorable for significant
development, and the current shear might get stronger during the
next 12-24 h.  Thus, little change in strength is forecast while
Karen crosses the eastern Caribbean, and the system may have trouble
maintaining tropical cyclone status.  The environment becomes more
favorable for development from 48 h on, and the intensity forecast
calls for slow strengthening during this time.  The new intensity
forecast has only minor adjustments from the previous forecasts.


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 watch is in
effect.  Tropical-storm-force winds, heavy rainfall, and flash
flooding are possible on these islands.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 13.1N  63.5W   35 KT  40 MPH
 12H  23/1200Z 13.9N  64.5W   35 KT  40 MPH
 24H  24/0000Z 15.3N  65.2W   35 KT  40 MPH
 36H  24/1200Z 16.9N  65.8W   35 KT  40 MPH
 48H  25/0000Z 18.7N  66.0W   35 KT  40 MPH
 72H  26/0000Z 22.4N  65.7W   40 KT  45 MPH
 96H  27/0000Z 25.0N  66.0W   45 KT  50 MPH
120H  28/0000Z 26.0N  67.0W   55 KT  65 MPH

$$
Forecaster Beven
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