Tropical Storm VANCE

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TROPICAL STORM VANCE DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212014
800 PM PDT FRI OCT 31 2014

Most of the available intensity analyses indicate that Vance has
weakened since the previous advisory and is barely holding on to
tropical cyclone status at that. The initial intensity of 35 kt is
based on a blend of satellite intensity estimates of 35 kt, 30 kt,
and 33 kt from TAFB, SAB, and UW-CIMSS ADT, respectively.

Visible and microwave fix positions over the past few hours suggest
that Vance has been moving slowly westward or just south of due
west, so the initial motion estimate is now 270/05 kt. Otherwise,
there is no significant change to the previous forecast track or
reasoning. A general westward motion should continue through
Saturday, followed by a turn to the west-northwest and northwest on
Sunday as Vance moves around the southwestern periphery of a
deep-layer ridge located to the north of the cyclone. As a
mid-tropospheric trough approaches Baja California on Monday, Vance
is forecast to move northward, followed by a turn and acceleration
toward the northeast on Tuesday. The latest model guidance is in
better agreement for this forecast cycle and is more tightly packed
as well. Therefore, the new NHC forecast track is basically just an
update of the previous advisory track, and closely follows the TVCE
consensus track model.

Although the convective cloud pattern of Vance has eroded
significantly during the past several hours, a small burst of deep
convection has recently developed over the center. Overall, however,
the cyclone has maintained a well-developed low-level wind field.
Dry mid-level air that has been plaguing Vance from the outset is
expected to give way to a more moist environment in the 12-48 hour
time period while the vertical wind shear remains rather low at less
than 5 kt. The result is that Vance is forecast to gradually
strengthen and become a hurricane by late Sunday. By 72 hours and
beyond, southwesterly vertical shear is expected to sharply increase
ahead of the aforementioned trough, causing the cyclone to rapidly
weaken. However, it is worth noting that Vance could reach a higher
peak intensity between the 48- and 72-hour periods before the
weakening trend begins. The NHC intensity forecast is similar to the
previous advisory forecast, and is a blend of the SHIPS and HWRF
intensity models.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z  9.5N 101.8W   35 KT  40 MPH
 12H  01/1200Z  9.5N 103.0W   40 KT  45 MPH
 24H  02/0000Z 10.0N 105.0W   45 KT  50 MPH
 36H  02/1200Z 11.1N 107.1W   55 KT  65 MPH
 48H  03/0000Z 12.6N 109.0W   65 KT  75 MPH
 72H  04/0000Z 16.5N 110.3W   65 KT  75 MPH
 96H  05/0000Z 20.1N 108.2W   40 KT  45 MPH
120H  06/0000Z 24.3N 105.3W   25 KT  30 MPH...INLAND

$$
Forecaster Stewart

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