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Hurricane Irma Discussion Number   7
NWS National Hurricane Center Miami FL       AL112017
1100 PM AST Thu Aug 31 2017

The period of rapid intensification that began in earnest about 24
hours ago appears to have ended, at least for now.  Although a ring
of very cold cloud tops continues to surround a small eye, the eye
appears to have filled somewhat during the evening hours. This may
be due to an eyewall replacement cycle that was noted to have begun
earlier today.  A lack of recent microwave imagery makes it
difficult to confirm that, however.  The initial intensity remains
100 kt based on a blend of subjective and objective Dvorak current
intensity estimates.

Even though the intensification of Irma seems to have stopped for
now, the hurricane is still embedded within a favorable environment.
For the next couple days, internal convective variability,
especially eyewall replacement cycles, may cause the intensity to
fluctuate up or down.  Most of the guidance through this period
shows very little change in strength.  Beyond 48 hours, Irma will
move over much warmer SSTs, and all of the hurricane models forecast
some strengthening.  The NHC forecast remains a little above the
intensity consensus, and is close to the HWRF and HMON models.

The initial motion estimate is 295/10 kt.  No significant changes
have been made to the track forecast.  While there remains good
agreement among the dynamical models that a ridge building over the
central Atlantic will steer Irma toward the west on Friday, and the
west-southwest through the weekend, there is large spread beyond
72 h.  For example, the GFS shows a somewhat weaker Irma and a
weaker ridge, forcing the hurricane to move slower and make a
sharper turn back toward the west-northwest.  On the other hand, the
ECMWF and HWRF depict a stronger ridge and a stronger hurricane on a
more southern track. Since my forecast calls for strengthening, the
NHC forecast remains south of the multi-model consensus, but is a
little north of the corrected consensus, HCCA.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 17.8N  35.6W  100 KT 115 MPH
 12H  01/1200Z 18.1N  37.0W  100 KT 115 MPH
 24H  02/0000Z 18.3N  39.2W  100 KT 115 MPH
 36H  02/1200Z 18.2N  41.5W  100 KT 115 MPH
 48H  03/0000Z 17.7N  43.8W  105 KT 120 MPH
 72H  04/0000Z 16.7N  48.2W  110 KT 125 MPH
 96H  05/0000Z 16.3N  52.4W  115 KT 130 MPH
120H  06/0000Z 17.0N  57.0W  120 KT 140 MPH

$$
Forecaster Zelinsky

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