Eastern Pacific Basin Tropical Cyclones

Tropical Storm Sandra Forecast Discussion


000
WTPZ44 KNHC 080838
TCDEP4

Tropical Storm Sandra Discussion Number   4
NWS National Hurricane Center Miami FL       EP192021
100 AM PST Mon Nov 08 2021

Sandra's convective pattern is characteristic of a sheared tropical 
cyclone, with the bulk of the convection now displaced into the 
northeastern quadrant of the cyclone owing to southwesterly vertical 
wind shear of around 20 kt. A 0257Z ASCAT-A pass revealed a tight, 
well-defined low-level circulation center, but with peak surface 
winds of only 28 kt in the northeastern quadrant. However, the 
intensity is being maintained at 35 kt since deep convection with 
cloud tops to -80C has re-developed in the vicinity of those ASCAT 
winds, possibly resulting in a local enhancement in those wind 
speeds.

Conventional satellite fixes and the aforementioned ASCAT wind data 
indicate that Sandra's forward speed has slowed considerably, and 
the initial motion estimate is now 285/06 kt. The cyclone is 
forecast to remain along the southern periphery of a deep-layer 
subtropical ridge for the next few days, resulting in a slow 
west-northwestward motion today, followed by a westward turn on 
Tuesday with that motion continuing into Wednesday. The new NHC 
forecast track is a little to the left or south of the previous 
advisory track, and lies down the middle of the NHC guidance 
envelope, which a tad south of the consensus models.

Moderate to strong southwesterly wind shear is expected to continue 
affecting Sandra for the next few days, while mid-level moisture 
and sea-surface temperatures gradually decrease. The combination of 
these unfavorable environmental conditions are expected to result in 
a gradual weakening of the cyclone, with Sandra now forecast to 
become a tropical depression later today and degenerate into a 
remnant low pressure system by late Tuesday. The new official 
intensity forecast is essentially the same as the previous advisory, 
and closely follows a blend of HCCA and IVCN intensity consensus 
models and the GFS and ECMWF global models.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 14.1N 116.3W   35 KT  40 MPH
 12H  08/1800Z 14.5N 117.5W   30 KT  35 MPH
 24H  09/0600Z 14.9N 119.1W   30 KT  35 MPH
 36H  09/1800Z 14.8N 121.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  10/0600Z 14.6N 123.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  10/1800Z...DISSIPATED

$$
Forecaster Stewart



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