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Hurricane Norman Discussion Number  18
NWS National Hurricane Center Miami FL       EP162018
800 AM PDT Sat Sep 01 2018

Although satellite intensity estimates indicate that Norman has
continued to weaken, the weakening trend appears to have abated.
This is based on recent infrared imagery showing a better developed
CDO feature accompanied by improved outflow, and also a well-defined
closed eye now depicted in a 1148Z AMSR and 1158Z SSMIS microwave
satellite images. The initial intensity has been lowered to 90 kt,
which is a blend of the various satellite intensity estimates, with
a little more weight placed on the TAFB estimate of T5.0/90 kt.

Norman's initial motion estimate is 270/10 kt. The aforementioned
eye noted in the microwave passes greatly helped with determining
the cyclone's location and past motion. Other than some slight
forward speed adjustments made in the first 24 hours due to the
faster initial motion, no significant changes were required to the
previous track forecast. Norman is forecast to move westward to
west-northwestward for the next several days as the hurricane moves
along the southern periphery of strong deep-layer ridge to the
north. The models are in excellent agreement on the track of Norman
through 72 h, and then diverge noticeably after that time with the
GFS taking Norman more westward in the general direction of the
Hawaiian Islands, whereas the ECMWF, HWRF, and HMON models keep
Norman well to the northeast of the islands. The official forecast
track lies close to the middle of the tightly packed guidance
envelope through 72 h, and then is close to the consensus aids HCCA
and FSSE after that.

The shear that has been affecting Norman appears to have weakened
some this morning, and that decreasing trend is expected to
continue throughout the forecast period, becoming near zero in
48-72 h according to the ECMWF model. The GFS model shows a
similar decreasing shear trend, but just not as much as the ECMWF
model. The HWRF and HMON models also have the shear decreasing and
do a complete reversal by re-strengthening Norman into a major
hurricane again during the next 24 h, followed by slow weakening
thereafter. For now, the official intensity forecast shows little
change in strength for the next 24 h, followed by slow weakening
during the remainder of the forecast period as the cyclone
encounters drier air and cooler sea-surface temperatures near 26C.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 16.2N 123.7W   90 KT 105 MPH
 12H  02/0000Z 16.3N 125.4W   90 KT 105 MPH
 24H  02/1200Z 16.9N 128.2W   90 KT 105 MPH
 36H  03/0000Z 17.8N 131.3W   85 KT 100 MPH
 48H  03/1200Z 18.7N 134.6W   85 KT 100 MPH
 72H  04/1200Z 20.3N 140.6W   70 KT  80 MPH
 96H  05/1200Z 21.3N 145.3W   65 KT  75 MPH
120H  06/1200Z 22.0N 148.6W   60 KT  70 MPH

$$
Forecaster Stewart

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