[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 071448
TCDAT3

Tropical Storm Gabrielle Discussion Number  16
NWS National Hurricane Center Miami FL       AL082019
1100 AM AST Sat Sep 07 2019

Gabrielle's structure does not look healthy this morning.  The
low-level circulation appears elongated, and it's difficult from
visible satellite imagery alone to identify a well-defined center.
The initial intensity is held at 45 kt, mainly based on continuity
and satellite estimates from TAFB and the UW-CIMSS SATCON.
We will analyze just-received ASCAT data and make modifications in
the afternoon advisory if necessary.

Gabrielle is swinging around the northeastern side of a mid- to
upper-level low, which has imparted a rather fast northwestward
motion of 310/15 kt.  A generally northwestward trajectory should
continue for the next 24 hours while Gabrielle remains positioned
between the deep-layer low and high pressure to its northeast.
After that time, Gabrielle should recurve around the high and then
become embedded in the mid-latitude westerlies beginning in 48
hours.  That steering regime should induce a northeastward
acceleration over the north Atlantic.  Despite the cyclone's
uncertain initial position, the track models are tightly clustered,
and the NHC track forecast was placed close to a consensus of the
GFS and ECMWF models.  This new forecast largely lies right on top
of the previous one.

Gabrielle's environment never really becomes ideal for
strengthening. For the next 24 hours, upper-level divergence and
moderate easterly shear should continue over the system.  By
48 hours, vertical shear is expected to increase further, and
Gabrielle will be moving over sub-26C waters as it heads toward the
north Atlantic.  Based on these conditions, some strengthening is
still shown in the official forecast, but it has been lowered from
the previous advisory to match the latest intensity guidance.
Based on the global model fields and phase-space diagrams,
Gabrielle is forecast to be fully extratropical by day 4, if not
sooner, and the system is likely to dissipate in the westerlies as
it heads toward the British Isles.


FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 31.4N  43.7W   45 KT  50 MPH
 12H  08/0000Z 32.4N  45.7W   45 KT  50 MPH
 24H  08/1200Z 34.1N  47.6W   50 KT  60 MPH
 36H  09/0000Z 36.5N  47.9W   55 KT  65 MPH
 48H  09/1200Z 39.4N  46.3W   60 KT  70 MPH
 72H  10/1200Z 45.0N  37.0W   65 KT  75 MPH
 96H  11/1200Z 51.5N  22.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  12/1200Z...DISSIPATED

$$
Forecaster Berg
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