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Tropical Storm Miriam Discussion Number  27
NWS Central Pacific Hurricane Center Honolulu HI   EP152018
1100 AM HST Sat Sep 01 2018
 
Under the effects of strong vertical wind shear, the low level
center of Miriam is now completely exposed, and a diminishing amount
of deep convection is confined to the north quadrant. Subjective
Dvorak current intensity estimates came in at 3.0/45 kt from HFO
and JTWC, while SAB gave a 3.5/55 kt. All final T numbers were 
lower. CIMSS ADT yielded a 3.0, and its earlier SATCON from 1642Z
produced 48 kt. Given the significant decay in the satellite
presentation, the initial intensity will be lowered to 50 kt,
making Miriam a rapidly weakening tropical storm.

The initial motion is north-northwest (345 degrees) at 11 kt, and a
turn toward the northwest is under way. A mid to upper level trough
to the northwest of Miriam is producing strong, southwesterly
vertical wind shear of 40 to 50 kt according to analyses, and the
shear will likely continue to increase through the next 18 hours. As
Miriam becomes increasingly shallow and less intense under the
effects of the shear, the system will be steered toward the
northwest under a greater influence of a deep ridge located far to
the northeast. The general northwestward motion will persist through
the duration of the tropical cyclone's existence, which will be a
few days at best. The forecast track lies just right of the middle
of the guidance envelope between HCCA and TVCE. Under the hostile
vertical wind shear and decreasing SSTs, Miriam is expected to
weaken to a post-tropical remnant low on Sunday, with dissipation
likely on Monday. The official forecast weakens Miriam at a slightly
slower rate than most guidance through the next 36 hours and is
close to HMNI and AVNI.

 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  01/2100Z 23.3N 141.5W   50 KT  60 MPH
 12H  02/0600Z 24.7N 142.5W   40 KT  45 MPH
 24H  02/1800Z 26.3N 144.1W   30 KT  35 MPH
 36H  03/0600Z 27.6N 146.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  03/1800Z 28.7N 148.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  04/1800Z...DISSIPATED
 
$$
Forecaster Wroe
 
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