000
WTPZ41 KNHC 290832
TCDEP1

Tropical Storm Narda Discussion Number   4
NWS National Hurricane Center Miami FL       EP162019
400 AM CDT Sun Sep 29 2019

Satellite images and Acapulco radar data show that the storm has
become a little better organized with some evidence of banding
features.  Upper-level outflow is fairly well defined over the
southern semicircle of the circulation while the cyclone continues
to experience some northeasterly shear.  Based on data from a
scatterometer overpass, the current intensity is set at 40 kt which
is also the mean of Dvorak estimates from TAFB and SAB.  The
intensity forecast for Narda is problematic and uncertain, since the
future strength of the cyclone depends on how much the cyclone will
interact with the mountainous land mass of southwestern Mexico
during the next few days.  Some of the models, such as the ECMWF
and GFS, take the cyclone inland within the next 24 hours and do
not show the system recovering from its land interaction in 24-48
hours.  A little more strengthening should occur today, assuming
the center remains offshore.  The official intensity forecast
assumes that the center will move along the coast within the next
day or so, and this would cause some weakening and disruption of
the circulation.  The NHC intensity forecast is in fairly close
agreement with the LGEM guidance.

The center is not easy to locate, but my best estimate of initial
motion is northwestward or 315/7 kt.  Over the next couple of days,
the tropical cyclone is likely to move generally northwestward along
the southwestern periphery of a large high pressure area.  Later in
the period, a trough approaching the northern Baja California
peninsula should cause the system to turn toward the
north-northwest.  The official forecast is similar to the previous
one, and close to the corrected dynamical model consensus guidance.

The primary threat from Narda is very heavy rainfall, which should
result in life-threatening flash flooding and mudslides over
portions of the southern coast of Mexico.  Rainfall totals of up to
15 inches are possible.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 16.0N 101.0W   40 KT  45 MPH
 12H  29/1800Z 17.4N 102.4W   45 KT  50 MPH
 24H  30/0600Z 19.3N 104.6W   35 KT  40 MPH...INLAND
 36H  30/1800Z 21.3N 106.4W   30 KT  35 MPH
 48H  01/0600Z 22.8N 107.9W   35 KT  40 MPH
 72H  02/0600Z 25.0N 109.5W   35 KT  40 MPH
 96H  03/0600Z 26.5N 110.0W   25 KT  30 MPH
120H  04/0600Z 27.5N 110.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Pasch