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Hurricane NORMAN


Hurricane Norman Discussion Number  19
NWS National Hurricane Center Miami FL       EP162018
200 PM PDT Sat Sep 01 2018

Since the previous advisory, a well-defined closed eye has remained
apparent in microwave satellite data, and a cloud-filled eye has
appeared in visible satellite imagery during the past couple of
hours. Satellite intensity estimated haven't changed since the
previous advisory, so the initial intensity remains 90 kt, which is
supported by a 1501Z SATCON estimate of 88 kt and a Dvorak CI value
of T5.0/90 kt.

Norman's initial motion estimate is now 275/12 kt based on microwave
and visible satellite eye position estimates. There are
no significant changes to the previous track forecast and reasoning.
The hurricane is expected to be steered by a strong deep-layer
subtropical ridge to the north, resulting in a westward motion for
the next 12-24 hours, followed by a west-northwestward motion at a
faster forward speed. The latest model guidance is tightly packed
about the previous forecast track through 96 hours, with much less
divergence after that compared to previous model runs. Therefore,
the new forecast track is essentially just an extension of the
previous advisory track, and lies close to a blend of the HCCA,
FSSE, and TVCE consensus track models.

The GFS and ECMWF models are forecasting the 15-20 kt of vertical
wind shear that has been affecting Norman to steadily decrease for
the next 60-72 hours, possibly becoming near zero if the ECMWF
upper-level wind forecasts verify. Since the hurricane is expected
to remain over 27 deg C and warmer SSTs for the next 48 hours, only
slow weakening is forecast and that is due mainly to occasional
intrusions of drier and more stable air coming in from the
northwest, where a large field of cold-air stratocumulus clouds is
currently lurking close by. The HWRF and HMON models continue to
forecast Norman to re-strengthen into a major hurricane during the
next 24 hours, but this scenario is being discounted at this time
due to Norman's proximity to the aforementioned stratocumulus cloud
field.  By 72 hours, increasing southwesterly shear and cooler SSTs
should combine to induce more significant weakening. The NHC
intensity forecast is similar to the HCCA and IVCN consensus model


INIT  01/2100Z 16.3N 125.1W   90 KT 105 MPH
 12H  02/0600Z 16.6N 127.0W   90 KT 105 MPH
 24H  02/1800Z 17.4N 130.1W   85 KT 100 MPH
 36H  03/0600Z 18.2N 133.2W   85 KT 100 MPH
 48H  03/1800Z 19.1N 136.5W   80 KT  90 MPH
 72H  04/1800Z 20.4N 142.0W   70 KT  80 MPH
 96H  05/1800Z 21.4N 146.4W   65 KT  75 MPH
120H  06/1800Z 22.2N 149.6W   60 KT  70 MPH

Forecaster Stewart