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Tropical Storm Norman Discussion Number  45
NWS Central Pacific Hurricane Center Honolulu HI   EP162018
1100 PM HST Fri Sep 07 2018
 
The exposed low-level circulation center (LLCC) of Norman remains
clearly evident in infrared and fog product satellite imagery this
evening, with diminishing deep convection confined only to the
northeast quadrant in a strongly sheared pattern. The subjective
Dvorak current intensity estimate came in at 3.5/55 kt from PHFO,
while JTWC estimated 3.0 or 45-50 kt using the subtropical method.
Objective intensity estimates are lower, with CIMSS SATCON showing
44 kt, and CIMSS ADT 2.8/41 kt. Recent satellite images since the
06Z synoptic time also show the remaining deep convection becoming
increasingly separated from the LLCC. Out of respect for the
stronger winds found around midday today by the 53rd Weather
Reconnaissance Squadron aircraft penetration as well as the 2001Z
ASCAT pass, will lower the initial intensity for this advisory only
slightly to 55 kt.   

The initial motion estimate for this advisory is 335/8 kt. Norman 
continues to move to the north-northwest between a deep-layer ridge 
centered to the east, and a longwave trough to the northwest. The
latest track guidance has shifted a bit more to the right, in better
agreement with the motion of Norman during the past 18 hours or so,
and shows the cyclone continuing on a north-northwest to northward
course during the next 2 to 3 days. The new track forecast lies 
close to the consensus HCCA and TVCE objective aids, and was shifted
only slightly to the right from the previous forecast. 

The CIMSS vertical wind shear estimate for this advisory is 230/56
kt, and is supported by recent GOES satellite-derived upper-level
wind retrievals. Very strong wind shear of 45-55 kt will persist
over Norman for the next 36 hours, with some decrease possible
thereafter. However, the system is forecast to be moving over cool
SSTs below 25C by that time. The combined effects of the shear and
increasingly cool water should cause Norman to steadily weaken
to a remnant low by 72 hours, then dissipate by day 5. It is worth
noting that the GFS and ECMWF models maintain Norman as a stronger
system, possibly transitioning toward extratropical after 72 hours,
while the hurricane dynamical and statistical models show more rapid
weakening. The official intensity forecast compromises between these
extremes, and delays dissipation as compared to the statistical
guidance, but does not keep Norman as strong as the GFS/EC and does
not show extratropical transition. If the recent loss of deep
convection near the LLCC persists, Norman could become post-tropical
considerable sooner than indicated in this forecast.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/0900Z 25.6N 153.6W   55 KT  65 MPH
 12H  08/1800Z 26.8N 154.0W   50 KT  60 MPH
 24H  09/0600Z 28.6N 154.3W   45 KT  50 MPH
 36H  09/1800Z 30.3N 154.3W   40 KT  45 MPH
 48H  10/0600Z 32.3N 154.0W   35 KT  40 MPH
 72H  11/0600Z 34.5N 154.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  12/0600Z 35.5N 156.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  13/0600Z...DISSIPATED
 
$$
Forecaster Jacobson
 
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