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Hurricane Norman Discussion Number  38
NWS Central Pacific Hurricane Center Honolulu HI   EP162018
500 AM HST Thu Sep 06 2018
 
Increasing southwesterly vertical wind shear of around 25 kt has
begun to take its toll Norman. Although deep convection remains 
vigorous in the inner core, the eye is no longer apparent on 
infrared imagery. Subjective Dvorak current intensity estimates came
in at 5.0/90 kt from all fix agencies. CIMSS ADT continues to
suggest a stronger system at 105 kt, and given the resilience of the
convection near the center, the initial intensity will be
conservatively dropped to 100 kt.

The initial motion is set at west-northwest (300 degrees) at 7 kt. 
Norman will gradually turn toward the northwest today as the 
hurricane heads into a weakness in the deep ridge centered far to 
the northeast. The northwestward motion will persist through the 
weekend as Norman interacts with a mid- to upper-level trough 
sitting to the northwest. The track forecast was changed little from
the prior advisory through 72 hours and was shifted slightly to the
right the prior advisory thereafter. The track forecast is nearest
to TVCE and HCCA and is down the middle of a guidance envelope that
has a significant increase in spread with time. Although the GFS and
ECMWF are slightly left of the official track, none of the reliable
guidance would lead to a direct impact from Norman on the main
Hawaiian Islands. However, as the tropical cyclone will remain in
our general vicinity for the next couple of days, people should
continue to monitor the progress of this system.

Weakening will continue. As Norman enters a weakness in the deep
ridge, it is encountering increasing southwesterly vertical wind
shear that is being produced by the mid- to upper-level trough
parked to the northwest. This wind shear will steadily increase
through Saturday and remain in place through at least Sunday. In
addition, SSTs will begin to cool later today. The combined effect
will be steady weakening, which will likely render Norman a
post-tropical remnant low on late Sunday or Monday. The intensity
forecast is essentially an update of the prior advisory and runs
down the middle of a fairly tightly clustered guidance envelope near
ICON through the next 72 hours. Guidance spread increases at 96
hours, and with vertical wind shear expected to remain high, the
forecast favors SHIPS, which continues to weaken Norman.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  06/1500Z 20.7N 150.5W  100 KT 115 MPH
 12H  07/0000Z 21.4N 151.3W   90 KT 105 MPH
 24H  07/1200Z 22.4N 152.4W   75 KT  85 MPH
 36H  08/0000Z 23.5N 153.5W   60 KT  70 MPH
 48H  08/1200Z 24.6N 154.8W   45 KT  50 MPH
 72H  09/1200Z 26.7N 156.8W   30 KT  35 MPH
 96H  10/1200Z 28.7N 158.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  11/1200Z 30.9N 160.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Wroe
 
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