440 
WTNT42 KNHC 240239
TCDAT2

Tropical Depression Kirk Discussion Number   7
NWS National Hurricane Center Miami FL       AL122018
1100 PM AST Sun Sep 23 2018

Kirk is looking increasingly disheveled in satellite imagery. A pair
of ASCAT passes between 2300 and 0000 UTC indicated that Kirk has
likely opened up into a trough of low pressure and no longer has a
closed surface circulation. However, no recent visible imagery or
surface observations are available to confirm this. Since the ASCAT
passes showed a few 25-30 kt wind vectors on the north side of the
alleged circulation, Kirk is being maintained as a 30 kt tropical
depression for now.

The ASCAT data showed almost no sign of the previous surface center
of Kirk, so the initial position was shifted significantly to the
west, closer to the wave axis. As a result, the NHC track forecast
has also been shifted significantly westward (faster) at all
forecast hours, especially from 12-72 h. Whether Kirk is a
tropical wave, depression, or storm, it should continue moving
rapidly westward for the next couple of days. By mid-week, the
system will reach a break in the subtropical ridge which will result
in a slower forward speed as it approaches and enters the Caribbean.
The NHC track forecast remains on the south side of the guidance
envelope, and is closest to the corrected consensus aid, HCCA.

It is likely that the fast forward speed is preventing Kirk from
becoming better organized and strengthening, and the global models
do not suggest that it will slow down substantially for the next
couple of days. While it is not explicitly reflected in the
forecast, Kirk could dissipate into a tropical wave at any time, if
it hasn't already. By the end of the forecast period, the slower
motion of Kirk could allow for some reorganization, however strong
vertical wind shear over the Caribbean will likely prevent the
system from significantly strengthening. The NHC intensity forecast
has been adjusted down, and is now essentially a blend of the global
and regional dynamical model forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z  9.4N  35.5W   30 KT  35 MPH
 12H  24/1200Z  9.8N  39.0W   30 KT  35 MPH
 24H  25/0000Z 10.0N  43.2W   35 KT  40 MPH
 36H  25/1200Z 10.3N  47.2W   35 KT  40 MPH
 48H  26/0000Z 10.6N  50.6W   35 KT  40 MPH
 72H  27/0000Z 11.7N  56.2W   35 KT  40 MPH
 96H  28/0000Z 13.0N  60.5W   35 KT  40 MPH
120H  29/0000Z 14.0N  65.0W   30 KT  35 MPH

$$
Forecaster Zelinsky