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Tropical Storm LORENA


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Tropical Storm Lorena Discussion Number   4
NWS National Hurricane Center Miami FL       EP152019
400 AM CDT Wed Sep 18 2019

Satellite imagery and a 0352 UTC ASCAT-B scatterometer pass indicate
that Lorena has strengthened this morning.  Subjective and
objective intensity estimates as well as the scatterometer overpass
support increasing the initial intensity to 50 kt for this advisory.

Although the cloud pattern has improved a bit during the past
several hours, moderate northeasterly shear still appears to be
impinging on the northern portion of the cyclone.  The
statistical-dynamical GFS and ECMWF Decay SHIPS intensity models
both indicate that this upper wind pattern will linger the
next couple of days.  Consequently, gradual strengthening is
expected which is consistent with the aforementioned DSHPS and the
NOAA HFIP HCCA intensity consensus model, and Lorena is forecast to
become a hurricane in 48 hours. Beyond that period, weakening should
commence as the cyclone traverses decreasing oceanic sea surface
temperatures and moves within increasing westerly shear.

An alternative intensity forecast is for Lorena to dissipate if
the center moves onshore in southwestern Mexico which the ECMWF is
showing.

The initial motion is estimated to be northwestward, or 310/12 kt.
A deep-layer ridge extending westward over Mexico from the western
Gulf of Mexico is forecast to steer Lorena toward the northwest
with a slight reduction in forward speed through day 5.  This
persistent synoptic steering flow should bring the cyclone near the
southwestern coast of Mexico Thursday and Friday.  The NHC forecast
is a little faster than the previous one and follows the NOAA HFIP
HCCA consensus which keeps the cyclone offshore.


Key Messages:

1. Lorena is forecast to cause heavy rain over portions of the
Mexican states of Guerrero, Michoacan, Colima, and Jalisco during
the next few days.  This rainfall may produce life-threatening flash
flooding and mudslides.

2. Tropical storm conditions are expected along a portion of the
southwestern coast of Mexico by late Wednesday.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 16.1N 103.0W   50 KT  60 MPH
 12H  18/1800Z 17.4N 104.1W   55 KT  65 MPH
 24H  19/0600Z 18.5N 104.9W   60 KT  70 MPH
 36H  19/1800Z 19.4N 105.5W   60 KT  70 MPH
 48H  20/0600Z 20.1N 106.4W   65 KT  75 MPH
 72H  21/0600Z 21.5N 108.7W   65 KT  75 MPH
 96H  22/0600Z 23.2N 111.1W   55 KT  65 MPH
120H  23/0600Z 25.6N 112.9W   45 KT  50 MPH

$$
Forecaster Roberts

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