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Hurricane Norman Discussion Number  17
NWS National Hurricane Center Miami FL       EP162018
200 AM PDT Sat Sep 01 2018

Norman continues to weaken due to the effects of moderate
northeasterly shear of about 20 kt, as analyzed in SHIPS
diagnostics. The hurricane has taken on a traditional IR shear
pattern structure, with a tight gradient of brightness temperatures
observed up-shear of the estimated center position. Satellite
intensity estimates have continued to drop and no longer support
keeping Norman at major hurricane strength. The initial intensity
has been lowered to 95 kt, just above the latest SATCON estimate,
but this still could be generous.

The shear affecting Norman is expected to continue for at least the
next 24 h. Some of the dynamical models hint that the shear could
relax between 24-48 h, which would likely bring an end to Norman's
weakening trend. While it is not explicitly reflected in the
intensity forecast, a decrease in shear could even allow the
hurricane to briefly restrengthen. Recent microwave imagery
indicates that the mid- to lower-level inner-core and eye of Norman
are still intact. If this structure can survive the next 24 h of
shear, reintensification would be more likely. By 72 h, the
hurricane will reach drier, more stable air and moderate SSTs, and
these factors will likely cause it to steadily weaken through the
remainder of the forecast period.

The cyclone appears to have finally turned westward, and the
initial motion is 265/7 kt.  No significant changes have been made
to the track forecast. Norman is still expected to move westward
to west-northwestward for the next several days, steered primarily
by an extensive deep-layer ridge to the north. The models remain
in good agreement on the track of Norman throughout the forecast
period, and the official track forecast is near the middle of the
guidance envelope and very close to the various consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0900Z 16.3N 123.0W   95 KT 110 MPH
 12H  01/1800Z 16.3N 124.4W   85 KT 100 MPH
 24H  02/0600Z 16.6N 126.8W   85 KT 100 MPH
 36H  02/1800Z 17.3N 129.8W   85 KT 100 MPH
 48H  03/0600Z 18.2N 132.9W   85 KT 100 MPH
 72H  04/0600Z 19.9N 139.1W   70 KT  80 MPH
 96H  05/0600Z 21.0N 143.5W   65 KT  75 MPH
120H  06/0600Z 21.5N 147.0W   60 KT  70 MPH

$$
Forecaster Zelinsky

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