Eastern Pacific Basin Tropical Cyclones

Tropical Depression Eighteen-E Forecast Discussion


000
WTPZ43 KNHC 070844
TCDEP3

Tropical Depression Eighteen-E Discussion Number  12
NWS National Hurricane Center Miami FL       EP182021
300 AM CST Sun Nov 07 2021

The disheveled convective appearance of the depression has not 
changed much since the previous advisory. However, recent ASCAT 
scatterometer surface wind data indicate that the wind field has 
actually become a little better defined. The ASCAT data also 
indicated a small patch of wind speeds of 27-28 kt north of the 
center, so the intensity remains at 30 kt for this advisory, which 
is consistent with the latest subjective and objective satellite 
intensity estimates.

The depression is moving due west now, or 270/12 kt. The small
cyclone is forecast to move westward to west-northwestward along
the southern periphery of a deep-layer subtropical ridge for the
next 5 days. This stable synoptic flow pattern has resulted in
little change to the previous forecast track, and the new NHC
advisory track lies along or just south of the middle of the
consensus track model envelope.

Although the associated convection remains poorly organized, the 
improved low-level wind field noted in the aforementioned ASCAT data 
wouldn't require much more convective organization for the cyclone 
to reach tropical storm status at any time during the next 60 h or 
so while the vertical wind shear remains low at only around 5 kt. By 
72 h, however, the shear is forecast to increase from the southwest 
and west at 20-25 kt while the cyclone moves westward into a 
progressively drier airmass. That negative combination is expected 
to induce weakening by 96 h, with the system degenerating into a 
remnant low by 120 h, if not sooner. The new NHC intensity forecast 
is just an update of the previous advisory, and closely follows a 
blend of the the GFS and ECMWF models intensity forecasts, which 
show a lower intensity on days 4 and 5 as compared to the higher 
HWRF-/HMON-based consensus intensity models.


FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z  8.2N 100.5W   30 KT  35 MPH
 12H  07/1800Z  8.5N 102.3W   30 KT  35 MPH
 24H  08/0600Z  8.9N 104.6W   30 KT  35 MPH
 36H  08/1800Z  9.3N 107.1W   35 KT  40 MPH
 48H  09/0600Z  9.7N 109.6W   35 KT  40 MPH
 60H  09/1800Z 10.1N 111.9W   35 KT  40 MPH
 72H  10/0600Z 10.2N 114.5W   35 KT  40 MPH
 96H  11/0600Z 10.4N 119.0W   30 KT  35 MPH
120H  12/0600Z 10.4N 123.6W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart



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