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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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