810 
WTPZ45 KNHC 262031
TCDEP5

Tropical Storm Miriam Discussion Number   3
NWS National Hurricane Center Miami FL       EP152018
200 PM PDT Sun Aug 26 2018

Miriam continues to gradually become better organized.  The latest
visible satellite images show a well-defined curved band that wraps
about three-quarters of the way around the center.  Despite the
improvement in organization, very recent ASCAT passes show maximum
winds of about 35 kt.  Therefore, the initial wind speed is held at
40 kt as a compromise between the ASCAT data and the higher
Dvorak-based estimates.

The tropical storm is moving westward at about 12 kt.  This westward
motion should continue during the next few days while a deep-layer
ridge remains anchored to the north of the tropical cyclone.  After
that time, the storm is forecast to turn to the northwest and then
the north as a mid- to upper-level low causes a significant break in
the subtropical ridge.  Although the models agree on this scenario,
there are some differences in where and when Miriam will make the
northward turn.  The NHC track forecast lies near the middle of the
guidance envelope, near the consensus aids.

Steady strengthening is likely during the next couple of days due to
the favorable environmental factors of low wind shear, high levels
of moisture, and warm SSTs of 27-28 deg C.  The latest intensity
models all show Miriam becoming a hurricane, and the HWRF model
shows the cyclone reaching major hurricane strength.  The NHC
intensity forecast continues to lean toward the higher end of the
model guidance, and it is in best agreement with HFIP Corrected
Consensus Approach model.  By the end of the forecast period, when
Miriam begins gaining latitude, slow weakening is expected due
to a decrease in SSTs and higher shear.

FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 13.6N 126.6W   40 KT  45 MPH
 12H  27/0600Z 13.6N 128.4W   50 KT  60 MPH
 24H  27/1800Z 13.7N 130.6W   65 KT  75 MPH
 36H  28/0600Z 13.7N 132.7W   80 KT  90 MPH
 48H  28/1800Z 13.7N 134.8W   90 KT 105 MPH
 72H  29/1800Z 13.7N 138.7W   90 KT 105 MPH
 96H  30/1800Z 15.8N 141.1W   85 KT 100 MPH
120H  31/1800Z 19.7N 141.7W   80 KT  90 MPH

$$
Forecaster Cangialosi