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Hurricane Norman Discussion Number  41
NWS Central Pacific Hurricane Center Honolulu HI   EP162018
1100 PM HST Thu Sep 06 2018
 
Norman's satellite presentation certainly has not improved since 
this afternoon, with deep convection continuing to shear northward 
away from the low level circulation center (LLCC). No eye is noted 
in infrared imagery and animation is not very helpful in locating 
the center. With 30 to 40 kt of vertical shear continuing across 
Norman and tilting its core this evening, we relied on timely 0341 
UTC and 0431 UTC SSMIS imagery to track the LLCC. Subjective Dvorak 
current intensity estimates were 4.5/77 kt from all three analysis 
centers, and ADT from UW-CIMSS was 66 kt. Given the continued 
apparent deterioration of this system, an initial intensity of 75
kt seems reasonable for this advisory. 

We rebested the 0000 UTC Norman position slightly to the left and 
slower to more align it with later SSMIS imagery. With this 
adjustment, the initial motion estimate for this advisory is a more 
northerly 325/7 kt. Norman is moving northwestward along the
western flank of a ridge and into an upper trough to its north.
Track guidance is tight through 48 hours, then pretty much all over
the map afterwards as each model handles a shear-decapitated Norman 
differently. We maintained a forecast track in the middle of the 
envelope, along ECMWF through 24 hours, then along TVCE consensus 
from 36 through 72 hours. The forecast track was tapped slightly to 
the right through 72 hours to account for the more northerly
initial motion, with the current track almost on top of the previous
one at 96 and 120 hours.

Norman will continue to experience very strong shear through 72
hours. This will weaken the tropical cyclone rather rapidly,
particularly in light of the cooler sea surface temperatures ahead.
Norman is expected to become a remnant low in 3 days.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  07/0900Z 22.5N 151.7W   75 KT  85 MPH
 12H  07/1800Z 23.3N 152.5W   60 KT  70 MPH
 24H  08/0600Z 24.4N 153.6W   50 KT  60 MPH
 36H  08/1800Z 25.5N 154.6W   40 KT  45 MPH
 48H  09/0600Z 26.5N 155.4W   35 KT  40 MPH
 72H  10/0600Z 28.5N 157.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  11/0600Z 30.5N 158.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  12/0600Z 32.5N 160.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Powell
 
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