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Hurricane Irma Special Discussion Number  25
NWS National Hurricane Center Miami FL       AL112017
800 AM AST Tue Sep 05 2017

This special advisory is being issued to increase the initial and
forecast intensity of Irma.

NOAA and U.S. Air Force Hurricane Hunter aircraft have recently
measured peak flight-level winds of around 170 kt and SFMR winds
of around 150 kt. Based on these data the initial intensity has
been increased to 150 kt, making Irma an extremely dangerous
category 5 hurricane. Some additional strengthening is still
possible, but fluctuations in intensity are likely during the next
couple of days due to eyewall replacement cycles.

No change was made to the previous track or wind radii forecast.

KEY MESSAGES:

1. Irma is expected to affect the northeastern Leeward Islands as
an extremely dangerous category 5 hurricane, accompanied by
life-threatening wind, storm surge, and rainfall. Hurricane warnings
are in effect for portions of the Leeward Islands. Preparations
should be rushed to completion, as tropical-storm force winds are
expected to first arrive in the hurricane warning area later today.

2. Irma is also expected to affect the British and U.S. Virgin
Islands and Puerto Rico as a dangerous major hurricane beginning
tomorrow, with life-threatening wind, storm surge, and rainfall.
Hurricane warnings have been issued for these areas, and tropical-
storm-force winds are expected to arrive in these areas by early
tomorrow.

3. Irma could directly affect Hispaniola, the Turks and Caicos, the
Bahamas, and Cuba as an extremely dangerous major hurricane later
this week. Residents in these areas should monitor the progress of
Irma and listen to advice given by officials.

4. There is an increasing chance of seeing some impacts from Irma in
the Florida Peninsula and the Florida Keys later this week and this
weekend.  Otherwise, it is still too early to determine what direct
impacts Irma might have on the continental United States.  However,
everyone in hurricane-prone areas should ensure that they have their
hurricane plan in place.


FORECAST POSITIONS AND MAX WINDS

INIT  05/1200Z 16.7N  57.7W  150 KT 175 MPH
 12H  05/1800Z 17.0N  58.9W  155 KT 180 MPH
 24H  06/0600Z 17.7N  61.5W  150 KT 175 MPH
 36H  06/1800Z 18.6N  64.2W  145 KT 165 MPH
 48H  07/0600Z 19.6N  67.0W  140 KT 160 MPH
 72H  08/0600Z 21.2N  72.5W  135 KT 155 MPH
 96H  09/0600Z 22.4N  77.2W  135 KT 155 MPH
120H  10/0600Z 24.0N  81.0W  130 KT 150 MPH

$$
Forecaster Brown

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