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Tropical Storm Miriam Discussion Number   7
NWS National Hurricane Center Miami FL       EP152018
200 PM PDT Mon Aug 27 2018

Miriam has become a little better organized since the last advisory,
and the convective banding has become better defined around the
low-level center.  However, this has not yet resulted in an
increase of the various satellite intensity estimates, which remain
mostly near 55 kt.  Based on this, the initial intensity remains a
possibly conservative 55 kt.  Satellite imagery continues to
indicate northwesterly to northerly vertical shear affecting Miriam,
with cirrus clouds from the outer band to the north blowing into the
central convection.

The initial motion is 270/13.  A large low- to mid-level ridge to
the north of Miriam should continue to steer it westward for the
next 36-48 h with some decrease in forward speed.  After that,
a large mid- to upper-level low to the northeast of the Hawaiian
Islands is expected to cause the ridge to break between 140W-150W,
with Miriam turning northwestward and north-northwestward in
response.  The track guidance is in good agreement on this
scenario, but there remain some differences in Miriam's forward
speed after recurvature between the faster ECMWF/UKMET and the
slower GFS.  The new forecast track is similar to the previous
track through 72 h, then is nudged a little to the east based on an
eastward shift in the consensus models.

The global models continue to suggest a gradual increase in
northwesterly shear over Miriam during the next day or so, followed
by decreased shear from 24-48 h.  There is some divergence in the
intensity guidance through 72 h, with the SHIPS/LGEM models showing
less strengthening than the HWRF/HMON/corrected consensus models.
This part of the new intensity forecast is little changed from the
previous forecast and lies between these two model camps. After
72 h, increasing southwesterly shear and cooler waters are expected
to cause Miriam to weaken.


FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 14.0N 131.8W   55 KT  65 MPH
 12H  28/0600Z 14.0N 133.5W   65 KT  75 MPH
 24H  28/1800Z 13.9N 135.5W   70 KT  80 MPH
 36H  29/0600Z 14.0N 137.5W   75 KT  85 MPH
 48H  29/1800Z 14.5N 139.0W   85 KT 100 MPH
 72H  30/1800Z 16.5N 141.0W   85 KT 100 MPH
 96H  31/1800Z 20.0N 142.0W   75 KT  85 MPH
120H  01/1800Z 24.5N 143.5W   50 KT  60 MPH

$$
Forecaster Beven

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