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Tropical Depression NINETEEN


Tropical Depression Nineteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL192017
500 AM AST Mon Nov 06 2017

GOES-16 night-time visible and infrared satellite imagery indicate
that convection associated with the well-defined low pressure
system located over the central Atlantic Ocean has increased and
become better organized during the past several hours. Satellite
intensity estimates were T1.5/25 kt from both TAFB and SAB at
0600Z.  Since that time, however, a burst of deep convection has
developed over the previously partially exposed low-level
circulation center, which had been located near the northwestern
edge of the large convective cloud mass. Given that the center is
now located farther into the deep convection, NHC objective
intensity estimates have increased to more than 30 kt. As a result,
advisories have been initiated on the nineteenth tropical depression
of the 2017 Atlantic hurricane season.

The initial motion estimate is 095/05 kt. The center of the cyclone
has been moving slowly eastward within the larger cyclonic gyre for
the past 12-18 hours, most likely due to the deep convection being
sheared toward the east.  However, the latest NHC model guidance
indicates that the recent eastward motion should be short-lived
since the larger gyre is forecast to begin moving northward within
the next 6 h or so. As the wind field contracts over the next 24
hours, the motion of the cyclone should stabilize and become less
erratic as deep-layer southerly steering flow becomes established
on the west side of a large-scale subtropical ridge. By 48 h and
beyond, southwesterly flow ahead of mid-latitude trough is forecast
to accelerate the system toward the northeast through 96 h. By
120 h, the cyclone should have merged with a frontal system or have
dissipated over the cold waters of the far north Atlantic. The
official track forecast lies close to a blend of the TVCN, TVCX,
and GFEX consensus track models.

The cyclone is currently embedded within a low-shear environment in
the col region between a weakening upper-level low located to the
southeast and a trough to the northwest. The vertical wind shear is
forecast by the GFS and ECMWF models to remain relatively low for
the next 36 h or so, which should allow for some modest
strengthening to occur despite sea-surface temperatures only being
around 25-26 deg C. Temperatures of 2-3 deg C colder-than-normal
in the mid- and upper-levels of the troposphere, however, should
act to offset the cooler SSTs, providing sufficient instability to
allow for deep convection to continue to develop. Model soundings
and the FSU Cyclone Phase-Space diagram indicate that extratropical
transition should begin shortly after 48 h when the cyclone reaches
about 40N latitude and moves over much cooler water. The NHC
intensity closely follows the HCCA and IVCN consensus models.


INIT  06/0900Z 28.9N  50.2W   30 KT  35 MPH
 12H  06/1800Z 30.0N  49.9W   35 KT  40 MPH
 24H  07/0600Z 32.0N  49.6W   40 KT  45 MPH
 36H  07/1800Z 35.4N  49.4W   45 KT  50 MPH
 48H  08/0600Z 39.4N  48.2W   45 KT  50 MPH
 72H  09/0600Z 49.0N  38.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  10/0600Z 59.0N  15.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  11/0600Z...DISSIPATED

Forecaster Stewart