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Hurricane Miriam Discussion Number  23
NWS Central Pacific Hurricane Center Honolulu HI   EP152018
1100 AM HST Fri Aug 31 2018
 
Miriam has been resilient under increasing vertical wind shear. A
ragged, cloud-filled eye has reappeared, despite southwesterly
vertical wind shear of about 25 to 35 kt according to SHIPS and
CIMSS, respectively. Subjective Dvorak current intensity estimates
came in at 5.0/90 kt across the board from HFO, SAB, and JTWC, while
CIMSS ADT yielded 80 kt. Given the longer term improvement in the
satellite presentation but noting the periodic filling of the eye
during the past several hours, the initial intensity has been raised
to 85 kt, which may be conservative.

The initial motion estimate is slightly east of due north (010 
degrees) at 9 kt. An SSMIS pass from 1352Z suggested some tilt
toward the northeast with height, which led to the placement of the
center near the southwestern edge of the eye as seen on
geostationary satellite imagery. Through the next 24 hours, Miriam
will continue to be steered northward by a mid to upper level trough
to the northwest and a deep ridge to the northeast. Later Saturday,
Miriam will begin a turn toward the northwest. This will occur as
the steering flow of the weakening system becomes increasingly
influenced by the low level ridge that will shift to the north of
Miriam. A general northwestward motion is expected to persist until
dissipation. The track was nudged to the right of the prior forecast
and lies near the middle of the guidance envelope, close to HCCA and
TVCE.

The slight increase in intensity will be short-lived. The already
vigorous, southwesterly vertical wind shear will increase through
the next 36 to 48 hours. In addition, SSTs, which are currently
running around 26.5 C, will steadily decrease along the forecast
track. Expect weakening to commence later today, with a sharp
decrease in intensity tonight through Sunday. The intensity
forecast goes nearly down the middle of the guidance envelope and is
close to the statistical models and FSSE. On this forecast, Miriam
will be a tropical storm by Saturday and will weaken to a remnant
low late Sunday or Monday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/2100Z 19.2N 141.1W   85 KT 100 MPH
 12H  01/0600Z 20.6N 141.2W   75 KT  85 MPH
 24H  01/1800Z 22.6N 141.7W   55 KT  65 MPH
 36H  02/0600Z 24.6N 143.0W   40 KT  45 MPH
 48H  02/1800Z 26.6N 144.7W   35 KT  40 MPH
 72H  03/1800Z 30.0N 148.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  04/1800Z...DISSIPATED
 
$$
Forecaster Wroe
 
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