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Hurricane Norman Discussion Number  34
NWS Central Pacific Hurricane Center Honolulu HI   EP162018
500 AM HST Wed Sep 05 2018
 
Norman appears to have rapidly intensified overnight. Although
the eye has become slightly less distinct during the past couple of
hours, the satellite fix agencies (SAB, JTWC, and PHFO) were in
unanimous agreement that the subjective Dvorak current intensity
estimate was 5.5/102 kt. In addition, the most recent UW-CIMSS
ADT estimate was 5.8/110 kt. Based on these estimates, we have
increased the initial intensity to 100 kt for this advisory.
 
Norman has been moving just south of due west, or 265 deg, at 10 kt.
It is being steered by a deep subtropical ridge located to the north
and northeast. The western edge of this ridge is forecast to erode
later today as an upper-level trough digs down toward the region
north of the Hawaiian Islands during the next couple of days. As a
result, the forecast guidance is showing an increasing spread in the
track forecasts starting in 48 hours. This is likely due to the way
the different models forecast the weakening of the western flank of
the ridge due to the upper-level trough. This weakening of the
ridge is expected to cause Norman to slow its forward motion and
gradually turn toward the west-northwest starting later today. This
will likely be followed by a turn toward the northwest starting
later tonight or early Thursday, and continuing into this weekend.
The latest forecast track has been shifted to the left of the
previous forecast, and remains close to the middle of the guidance
envelope through the next 2 days. Even though the guidance spread
increases during days 3 through 5, all of the models support the
general northwestward motion persisting. The latest official
forecast is also very close to the FSSE, TVCE, HCCA and GFEX
consensus model guidance.
 
Norman is expected to remain a hurricane for the next couple of
days. The latest CIRA ocean heat content (OHC) analysis appears to
support it remaining near major hurricane intensity today. Vertical
wind shear has gradually increased to near 15 kt based on the
latest UW-CIMSS estimate, which may be contributing to some of the 
degradation of the eye this morning. By tonight, most of the
guidance is in good agreement that Norman will start to weaken under
the effects of increasing southwesterly vertical wind shear, cooler
SSTs, and drier environmental conditions. This weakening will likely
persist through day 5, when Norman is forecast to become a remnant
low. The intensity forecast follows similar trends of the prior
advisory, and favors the latest ICON guidance.

The NOAA Gulfstream IV aircraft is scheduled to conduct another 
mission to sample the environment around Norman later today. The
valuable data collected during this mission will be used to improve
the initialization of the various hurricane forecast models that we
use to predict the motion and intensity of Norman later today and
tonight.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/1500Z 19.5N 147.7W  100 KT 115 MPH
 12H  06/0000Z 19.8N 148.9W  100 KT 115 MPH
 24H  06/1200Z 20.4N 150.2W   90 KT 105 MPH
 36H  07/0000Z 21.4N 151.3W   80 KT  90 MPH
 48H  07/1200Z 22.6N 152.3W   70 KT  80 MPH
 72H  08/1200Z 24.9N 154.3W   45 KT  50 MPH
 96H  09/1200Z 27.0N 156.5W   30 KT  35 MPH
120H  10/1200Z 28.6N 158.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Houston
 
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