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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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