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Tropical Storm Miriam Discussion Number  14
NWS National Hurricane Center Miami FL       EP152018
800 AM PDT Wed Aug 29 2018

Although Miriam remains a sheared tropical cyclone, recent
geostationary satellite data and a 1002 UTC AMSR2 microwave
overpass indicates that there has been some improvement in the
structure of the cyclone.  The microwave data showed an increase in
banding over the eastern portion of the circulation and less
separation between the convection and the low-level center.
Therefore, the initial intensity is increased to 60 kt, which is a
blend of the most recent subjective Dvorak classifications and
objective T-numbers from UW/CIMSS.  The northwesterly shear over
the cyclone appears to have abated slightly, and a further slight
reduction in shear could allow Miriam to reach hurricane strength
within the next 24-36 h.  Most of the intensity guidance agrees,
and the NHC intensity forecast has been increased slightly for the
first 36 h.  After that time, increasing shear and cooler waters are
expected to cause Miriam to weaken fairly quickly and the system is
forecast to become a remnant low by day 4.

Miriam continues to move westward or 275/10 kt. The cyclone is
approaching the western edge of the subtropical ridge, and the
global models indicate that Miriam will slow down and turn
west-northwestward very soon.  By Thursday, a large mid- to
upper-level trough to the northeast of the Hawaiian Islands is
expected to cause Miriam to turn northwestward, then northward
through 72 hours.  At days 3 and beyond, there continues to be
significant model differences with the ECMWF still taking Miriam
faster and much farther northward, while the GFS moves a much
weaker Miriam westward.  Since Miriam is forecast to weaken and
become a shallow system around that time, the NHC forecast leans
toward the more westward scenario, but is not as far south and west
as the GFS. The new NHC track is south of the various consensus aids
at day 5, and is in best agreement with the GFS ensemble mean
and UKMET model.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 14.2N 139.4W   60 KT  70 MPH
 12H  30/0000Z 14.4N 140.6W   65 KT  75 MPH
 24H  30/1200Z 15.1N 141.6W   65 KT  75 MPH
 36H  31/0000Z 16.3N 142.0W   65 KT  75 MPH
 48H  31/1200Z 17.9N 142.1W   60 KT  70 MPH
 72H  01/1200Z 21.0N 142.9W   45 KT  50 MPH
 96H  02/1200Z 23.8N 145.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  03/1200Z 26.7N 149.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown

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