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HURRICANE BLAS DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP032016
200 AM PDT THU JUL 07 2016

Blas continues to maintain an impressive satellite presentation,
with a distinct 20 n mi wide eye surrounded by a ring of cold
convective tops.  Overall, the cyclone has been steady-state for
the last 24 hours or so, consistent with some annular hurricane
characteristics such as minimal convective banding and a large eye.
The initial intensity remains 110 kt based on the latest Dvorak
classifications of T5.5/6.0 from TAFB and SAB.

The hurricane will be moving over cooler waters and into a more
stable atmospheric environment during the next 12 to 24 hours, which
should result in the onset of weakening.  Weakening should continue
after that time, with Blas expected to move over SSTs of about 24C
in 48 hours.  Deep convection is expected to dissipate late in the
period, and Blas should become post-tropical in 4 days, or perhaps a
bit sooner.  The official forecast is close to the latest IVCN
intensity consensus aid.

The initial motion estimate is 290/09, as Blas continues to be
steered around the southwestern periphery of a distant mid-level
ridge centered over northern Mexico.  The hurricane is forecast to
turn northwestward in 24-36 hours as it reaches the western edge of
the ridge, and the track model guidance is in good agreement on this
scenario.  Through 48 hours the NHC track has been shifted a bit
north of the previous one following the latest trend in the
guidance.  Afterward, most of the guidance shows a continued
west-northwestward or northwestward motion through 72 hours as Blas
interacts with an upper-level closed low northeast of the Hawaiian
Islands, followed by the shallow post-tropical Blas turning
westward.  The ECMWF continues to show less interaction with the
upper-level low, and turns Blas westward and west-southwestward at
days 4 and 5.  Compared to 24 hours ago, the GFS-based guidance has
shifted southward and the ECMWF has trended a bit northward,
suggesting that a consensus approach is still the best solution. The
new NHC track at days 3 through 5 is close to the previous one and
near the middle of the guidance envelope.  This track is a little
south of the latest multi-model consensus but well north of the
ECMWF.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 15.9N 126.4W  110 KT 125 MPH
 12H  07/1800Z 16.4N 127.6W  100 KT 115 MPH
 24H  08/0600Z 17.2N 129.1W   85 KT 100 MPH
 36H  08/1800Z 18.3N 130.4W   70 KT  80 MPH
 48H  09/0600Z 19.5N 131.8W   60 KT  70 MPH
 72H  10/0600Z 21.5N 135.0W   40 KT  45 MPH
 96H  11/0600Z 22.0N 139.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  12/0600Z 22.0N 143.5W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brennan

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