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Tropical Storm Irma Discussion Number   3
NWS National Hurricane Center Miami FL       AL112017
1100 PM AST Wed Aug 30 2017

Irma continues to become better organized, with the development of
a small CDO feature and increased banding near the center.  An
earlier high-resolution Windsat microwave overpass showed that Irma
has a tight inner core and a low-level eye-like feature was
present.  A Dvorak classification of T3.5 from TAFB is the basis
for the initial intensity of 55 kt.  Irma is expected to steadily
strengthen during the next couple of days while it moves through a
low-shear and moist environment, and remains over warm sea
surface temperatures.  After that time, slightly cooler SSTs and
lower mid-level moisture may temper the intensification process.
However, the statistical aids, HWRF, and most of the consensus
models make Irma a major hurricane by the end of the forecast
period.  The NHC forecast is fairly similar to the previous advisory
through 48 hours, but is above the earlier forecast thereafter.  The
new official intensity forecast could still be a little conservative
as it remains a little below the SHIPS/LGEM guidance and the ICON
consensus at days 4 and 5.

Irma is moving westward at about 10 kt to the south of deep-layer
ridge over the eastern Atlantic.  The track forecast reasoning is
about the same as the previous advisory, with Irma expected to turn
west-northwestward on Thursday, then continue on that heading
for a couple of days.  The high pressure ridge over the central
Atlantic is forecast to strengthen later this week, which is
expected to result in Irma turning west-southwestward by the
weekend.  There is still some spread among the track models, so the
NHC forecast lies near a blend of the typically reliable GFS and
ECMWF, and the HFIP corrected consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  31/0300Z 16.4N  32.2W   55 KT  65 MPH
 12H  31/1200Z 16.8N  33.6W   65 KT  75 MPH
 24H  01/0000Z 17.3N  35.5W   75 KT  85 MPH
 36H  01/1200Z 17.7N  37.3W   85 KT 100 MPH
 48H  02/0000Z 18.0N  39.5W   90 KT 105 MPH
 72H  03/0000Z 17.6N  44.3W   95 KT 110 MPH
 96H  04/0000Z 16.8N  49.0W  100 KT 115 MPH
120H  05/0000Z 16.2N  53.5W  105 KT 120 MPH

$$
Forecaster Brown

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