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WTPZ41 KNHC 010236
TCDEP1

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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