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Hurricane Irma Discussion Number  10
NWS National Hurricane Center Miami FL       AL112017
500 PM AST Fri Sep 01 2017

Well, that eyewall replacement cycle didn't last long.  Satellite
images indicate that the cycle is now complete, with Irma displaying
a larger warm eye.  The initial wind speed has been set to 105 kt,
in agreement with the CIMSS ADT.  Since the eyewall cycle is
finished, some strengthening is possible, although SSTs are
currently pretty marginal.  Although no increase in winds is shown
in the short term, this could be conservative.  During the next few
days, water temperatures along the track will warm significantly,
but there could be some higher shear, and of course more eyewall
replacements.  The forecast is a compromise between the
statistical/dynamical models, which bring the intensity down then up
again, versus the global models and hurricane models, which show a
rather strong cyclone.

The westward turn of Irma has begun, and the current motion is
275/12.  A building mid-level high should cause the hurricane to
turn west-southwestward tomorrow and continue through early next
week.  Later on, Irma should reach the southern periphery of the
ridge, and begin to move west-northwestward.  The biggest change
since the last forecast is that the GFS and its ensemble has
trended southwestward, toward the unwavering ECMWF model on the
track forecast.  Given the trend in guidance, little change is made
to the official track prediction, although the corrected consensus
models and the HWRF are now southwest of the latest forecast.

KEY MESSAGES:

1. Irma is expected to be a major hurricane when it approaches the
Lesser Antilles early next week, producing rough surf and rip
currents.  Irma could also cause dangerous wind, storm surge, and
rainfall impacts on some islands, although it is too soon to specify
where and when those hazards could occur. Residents in the Lesser
Antilles should monitor the progress of Irma through the weekend and
listen to any advice given by local officials.

2. It is much too early to determine what direct impacts Irma will
have on the continental United States. Regardless, everyone in
hurricane-prone areas should ensure that they have their hurricane
plan in place, as we are now near the peak of the season.


FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 18.8N  39.1W  105 KT 120 MPH
 12H  02/0600Z 18.9N  40.9W  105 KT 120 MPH
 24H  02/1800Z 18.5N  43.4W  105 KT 120 MPH
 36H  03/0600Z 17.9N  45.7W  105 KT 120 MPH
 48H  03/1800Z 17.2N  47.9W  105 KT 120 MPH
 72H  04/1800Z 16.4N  52.2W  110 KT 125 MPH
 96H  05/1800Z 17.0N  56.5W  110 KT 125 MPH
120H  06/1800Z 19.0N  61.0W  115 KT 130 MPH

$$
Forecaster Blake

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