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Tropical Storm Lidia Discussion Number   7
NWS National Hurricane Center Miami FL       EP142017
300 AM MDT Thu Aug 31 2017

Scatterometer data and microwave images indicate that Lidia has a
deformed circulation, with what appears to be two lobes of
vorticity rotating around a common center.  The unmanned NASA Global
Hawk flew very near the centroid of the circulation last evening
and provided a better estimate of Lidia's central pressure (about
998 mb at the time).  In addition, a dropsonde released to the east
of the center measured a mean boundary layer wind of 45 kt, which
equates to a surface wind a little over 35 kt.  Assuming the
dropsonde did not sample the highest winds, and given that deep
convection has become more organized into two distinct clusters
since that time, the initial intensity is raised to 40 kt.

Lidia is moving north-northwestward, or 335/7 kt, between a
mid-level high centered over central Mexico and a cyclonic gyre
located to the west over the Pacific.  This motion should continue
for the next 36 hours, but then after that time, high pressure over
the southwestern United States should force Lidia to turn
northwestward and west-northwestward on days 2 through 5.  Most of
the spread in the track models is related to Lidia's forward speed,
and there is a notable disparity between the faster GFS and slower
ECMWF models.  The new NHC track forecast is a little faster than
the previous one to better match the speeds of the TVCN multi-model
consensus and the HFIP Corrected Consensus Approach (HCCA).

Even though Lidia is in an environment of low shear and over very
warm waters, the storm's large size and lack of an inner core are
likely to prevent fast strengthening before the center reaches the
Baja California peninsula.  Since the ambient environment is
favorable, the NHC forecast continues to call for modest
strengthening and still shows a peak intensity of 55 kt in about 24
hours, which is in line with HCCA.  Weakening is expected after 24
hours due to the center moving up the spine of the Baja California
peninsula, but tropical-storm-force winds are likely to spread up
the Gulf of California well east of the center.  Lidia is forecast
to become a remnant low by day 3 due to its interaction with land,
and further weakening is anticipated over the cold waters of the
California Current on days 4 and 5.

Lidia is a large system accompanied by very heavy rains which are
already occurring over portions of western Mexico and Baja
California Sur.  Regardless of how strong Lidia becomes,
life-threatening flash floods and mudslides will be a significant
hazard over these areas.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0900Z 21.3N 109.4W   40 KT  45 MPH
 12H  31/1800Z 22.3N 109.9W   50 KT  60 MPH
 24H  01/0600Z 23.6N 110.5W   55 KT  65 MPH
 36H  01/1800Z 25.1N 111.4W   45 KT  50 MPH...INLAND
 48H  02/0600Z 26.7N 112.6W   40 KT  45 MPH...INLAND
 72H  03/0600Z 29.2N 115.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  04/0600Z 30.0N 119.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  05/0600Z 30.5N 121.5W   15 KT  15 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

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