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Tropical Storm Norman Discussion Number 43
NWS Central Pacific Hurricane Center Honolulu HI EP162018
1100 AM HST Fri Sep 07 2018
Strong southwesterly shear ripped thunderstorms from the center of
Norman overnight, and the partially exposed low-level circulation
center (LLCC) is now evident in visible satellite imagery. With
thunderstorms limited to the northern semicircle, subjective Dvorak
intensity estimates ranged from 3.0/55 kt from PGTW/SAB to 4.0/65
kt from PHFO. A blend of these data supports lowering the initial
intensity to 60 kt for this advisory.
Norman is moving toward the north-northwest between a deep-layer
ridge centered to the east, and a longwave trough to the northwest,
and the initial motion estimate for this advisory is 340/8 kt. A
general motion toward the north-northwest and then north is
expected to continue as the steering flow changes little through day
3. The updated forecast track again is shifted to the right of the
previous due to significant shifts in the guidance envelope, and the
updated forecast lies close to the HCCA and TVCE. Toward the end of
the forecast period, a severely weakened and shallow Norman is
expected to briefly move toward the northwest before dissipating on
day 5.
Norman will continue to weaken as it will remain embedded in an
environment characterized by 40-50 kt of vertical wind shear. The
updated intensity forecast closely mimics the previous forecast and
ICON. Continued rapid weakening in the short term should taper off
somewhat on days 2 and 3 as the low-level remnant slowly spins down
over gradually decreasing SSTs. A more rapid decrease in SSTs on
days 4 and 5 should ensure decay, then dissipation. The official
forecast delays dissipation as compared to the statistical
guidance, with preference given to dynamical model guidance that
indicates that Norman will weaken more slowly.
FORECAST POSITIONS AND MAX WINDS
INIT 07/2100Z 24.0N 152.8W 60 KT 70 MPH
12H 08/0600Z 25.0N 153.6W 50 KT 60 MPH
24H 08/1800Z 26.4N 154.6W 45 KT 50 MPH
36H 09/0600Z 27.8N 155.0W 40 KT 45 MPH
48H 09/1800Z 29.4N 154.7W 35 KT 40 MPH
72H 10/1800Z 32.0N 154.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 11/1800Z 34.5N 156.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 12/1800Z...DISSIPATED
$$
Forecaster Birchard
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