Eastern Pacific Basin Tropical Cyclones

Tropical Depression Sixteen-E Forecast Discussion


000
WTPZ41 KNHC 100858
TCDEP1

Tropical Depression Sixteen-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP162021
400 AM CDT Sun Oct 10 2021

The system we have been monitoring over the last several days off 
the southern coast of Mexico has been gradually improving in 
organization. An earlier ASCAT-A pass at 0257 UTC indicated that a 
closed surface vortex was developing, especially after investigating 
the ambiguity wind solutions from the instrument. In addition, the 
0600 UTC subjective Dvorak from TAFB was at T2.0/30 kt, which is in 
good agreement with the peak winds (29 kt) from the earlier 
scatterometer data. Since that time, convection near the estimated 
center has only increased in coverage and intensity. Therefore, 
advisories are being initiated on TD16-E, the first tropical 
cyclone in the East Pacific basin in nearly a month. The initial 
intensity has been set at 30 kt in agreement with the scatterometer 
and satellite intensity estimate.

The current motion of the depression is estimated at 290/15 kt, 
though some uncertainty exists given the system is in its formative 
stages. At present, the cyclone is situated on the equatorward side 
of an expensive mid-level ridge centered over Mexico that stretches 
westward into the East Pacific. This ridge should continue to steer 
the tropical cyclone to the west-northwest over then next day or so. 
Thereafter, a strong shortwave trough is forecast to dig into the 
western United States, creating a pronounced weakness in the 
mid-level ridge steering the system. The net result of this synoptic 
pattern change is that the tropical cyclone will likely bend 
sharply right as the ridge becomes oriented to its east, leading to 
a turn north to then northeastward in the 48-72 hour forecast. This 
track evolution would likely steer the system to the mainland 
Mexican coast in around 96 hours. The latest track guidance is in 
pretty good agreement on the general track, though investigating the 
GFS and ECMWF ensembles solutions reveals significant uncertainty 
in the along-track spread of the current forecast track. The 
initial NHC track forecast has been chosen to lie near the consensus 
aids, splitting the difference between the TVCA and HCCA solutions.

The environment over the depression appears quite favorable for 
intensification, with low shear (around 10 kt) high mid-level 
moisture (around 70 percent) and warm sea-surface temperatures 
(29-30 C) expected to persist for the next three days. It may take 
12-24 hours for an inner core to become established, but after this 
structural change occurs, the system appears poised for substantial 
intensification. In fact, the latest GFS-SHIPS guidance indicates a 
44 percent chance of a 65 knot increase in intensity over the next 
72 hours. The first NHC intensity forecast follows suit, showing a 
peak intensity of 95 kt in 72 hours. It is worth noting that this 
intensity forecast is less than some of the more bullish guidance, 
including the latest HFIP corrected consensus approach (HCCA) and 
this initial forecast could be conservative.


FORECAST POSITIONS AND MAX WINDS

INIT  10/0900Z 14.3N 102.9W   30 KT  35 MPH
 12H  10/1800Z 15.1N 105.0W   35 KT  40 MPH
 24H  11/0600Z 15.8N 107.2W   45 KT  50 MPH
 36H  11/1800Z 16.6N 108.6W   60 KT  70 MPH
 48H  12/0600Z 17.8N 109.6W   75 KT  85 MPH
 60H  12/1800Z 19.0N 109.8W   85 KT 100 MPH
 72H  13/0600Z 20.7N 109.4W   95 KT 110 MPH
 96H  14/0600Z 25.2N 106.4W   75 KT  85 MPH...INLAND
120H  15/0600Z...DISSIPATED

$$
Forecaster Papin



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