WTPA43 PHFO 011448
Hurricane Miriam Discussion Number 26
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 AM HST Sat Sep 01 2018
Shear continues to profoundly affect the core of Miriam this
morning, with the low level circulation center (LLCC) now mostly
exposed along the southwest flank of diminishing deep convection.
UW-CIMSS reports 41 kt of vertical wind shear across this system,
up from 34 kt last evening. Good outflow exists only to the north
through north-northeast, consistent with the shear direction.
Subjective Dvorak current intensity estimates decreased to 4.0/65
kt from PHFO and SAB, and to 3.5/55 kt from JTWC. ADT from UW-CIMSS
was 65 kt. Initial intensity for this advisory is set at 65 kt
which, like last time, represents weakening but may still be a bit
too high given the rapidly deteriorating satellite presentation.
Initial motion is 355/10 kt as Miriam continues northward between
an upper trough to the northwest and a deep ridge to the northeast.
Track guidance continues to depict a turn toward the
north-northwest through Sunday and toward the northwest on Monday.
The guidance envelope is rather tight through 48 hours, with HWRF
depicting a sharper turn toward the left as it forecasts rapid
dissipation of this system and a greater role for low level steering
in the near term. In contrast, ECMWF lies along the right side of
the guidance envelope. The forecast track closely follows the
previous one, neatly following TCVE consensus, but adjusted slightly
to the right through 24 hours to account for initial motion.
Miriam will continue to weaken in the face of increasing shear and
sub-26 degree C SSTs through the forecast period, with this system
forecast to dissipate at 72 hours. We expect Miriam will weaken to
a tropical storm later today before becoming a post tropical
remnant low early Monday. Some guidance dissipate Miriam earlier,
with DSHIP and LGME calling for this at 36 and 48 hours,
respectively. Our intensity curve follows HMNI through 12 hours,
then along HWRF through dissipation.
FORECAST POSITIONS AND MAX WINDS
INIT 01/1500Z 22.2N 141.3W 65 KT 75 MPH
12H 02/0000Z 23.6N 141.9W 55 KT 65 MPH
24H 02/1200Z 25.4N 143.4W 40 KT 45 MPH
36H 03/0000Z 27.1N 145.2W 30 KT 35 MPH
48H 03/1200Z 28.7N 147.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
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