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Tropical Storm NORMAN

Tropical Storm Norman Discussion Number  46
NWS Central Pacific Hurricane Center Honolulu HI   EP162018
500 AM HST Sat Sep 08 2018
Deep convection near the exposed low-level circulation center
(LLCC) of Norman dissipated around 07Z last evening, and has not 
returned as of advisory time, with only a small area of convection
present about 90 nm north of the center. The LLCC has remained
clearly visible in infrared and fog product satellite imagery during
the night. The subjective Dvorak current intensity estimate came in
at 3.0/45 kt from PHFO, while JTWC estimated 3.0 or 45-50 kt using
the subtropical method. The latest objective estimates remain lower,
with CIMSS SATCON showing 43 kt, and CIMSS ADT 2.3/32 kt. The
overnight ASCAT pass missed Norman, but a 0648Z ScatSat pass found
winds of 40 kt in the northeast quadrant. The initial intensity is
lowered to 50 kt for this advisory, reflecting an assumed gradual
spindown from the stronger winds measured by the 53rd Weather
Reconnaissance Squadron aircraft on Friday, and this may be

Norman appears to have turned more to the northwest during the
night, likely in response to the loss of deep convection, and the
initial motion estimate for this advisory is 320/8 kt. All of the
reliable guidance insists that the current northwest motion is
temporary, and that Norman will quickly resume a north-northwest
motion today, becoming almost due north thereafter, as it moves
between a deep-layer ridge centered to the east and a cutoff low
to the west. The guidance envelope did not shift much from the 
previous advisory. The new track forecast is on the left side
of the reliable guidance for the first 24 hours due to the current
motion, then near the previous forecast and the consensus HCCA and
TVCE aids thereafter. 

The CIMSS vertical wind shear estimate for this advisory is 235/52
kt, and very strong southwest vertical wind shear of 45 to 55 kt is
expected to persist over Norman for the next 36 hours or so, with
some decrease possible thereafter. However, the system is forecast
to be moving over cool SSTs below 25C by that time. Also, the SHIPS
and experimental ECMWF-based SHIPS guidance now both categorize
Norman as extratropical in 24 hours. This seems plausible given the
asymmetric wind field observed by the ScatSat pass, the fact that
the system already is acquiring a rather subtropical appearance, and
Norman's increasingly shallow warm core as depicted by the FSU
phase-space diagrams. The new intensity forecast continues to weaken
Norman, and makes it a post-tropical gale center in 36 hours. If
Norman does not regain deep convection near the LLCC soon, it will
likely be declared post-tropical considerably sooner than shown in
this forecast.
INIT  08/1500Z 26.0N 154.4W   50 KT  60 MPH
 12H  09/0000Z 27.4N 154.8W   45 KT  50 MPH
 24H  09/1200Z 29.1N 154.9W   40 KT  45 MPH
 36H  10/0000Z 31.2N 154.7W   40 KT  45 MPH...POST-TROPICAL
 48H  10/1200Z 32.9N 154.5W   35 KT  40 MPH...POST-TROPICAL
 72H  11/1200Z 34.5N 155.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  12/1200Z 35.5N 156.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  13/1200Z...DISSIPATED
Forecaster Jacobson