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Hurricane IRMA (Text)


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Hurricane Irma Discussion Number  29
NWS National Hurricane Center Miami FL       AL112017
500 AM AST Wed Sep 06 2017

Irma continues as a Category 5 hurricane this morning, having
passed over Barbuda a few hours ago.  Earlier data from an Air Force
Reserve Hurricane Hunter aircraft included SFMR winds near 155 kt
and that the central pressure had fallen to 914 mb inside the 25 n
mi wide eye.  There has been little change in the satellite
appearance of the hurricane since that time, so the initial
intensity remains 160 kt.

The initial motion is 285/14.  Irma is currently being steered by
the subtropical ridge to the north, and a general west-
northwestward motion on the south side of the ridge is expected
during the next 48-72 h.  This portion of the forecast track is
little changed and is in best overall agreement with the ECMWF
model.  The forecast has become more uncertain after 72 h due to
large eastward shifts by the ECMWF, Canadian, and HWRF models
related to forecasts of the mid- to upper-level trough over the
southeastern United States.   The bulk of the guidance now calls for
Irma to turn northward between 78W-80W, moving near or over the
Florida east coast or the northwestern Bahamas.  The official
forecast has also been shifted eastward, but out of respect for the
previous forecast and the possibility the guidance may shift back
to the west, it lies to the left of the bulk of the guidance.  The
forecast now calls for landfall in south Florida between 96-120 h.
Users are reminded to not focus on the exact forecast track,
especially at the longer ranges, since the average NHC track errors
are about 175 and 225 statute miles at days 4 and 5, respectively.

Irma is likely to remain in a light shear, warm water, environment
for the next 3 to 4 days.  The intensity guidance continues to show
slow weakening during this time, and this part of the intensity
forecast is little changed from the previous advisory, with Irma
remaining a strong hurricane during this time.  The intensity
forecast is lowered at 120 h due to the forecast landfall, and even
if Irma stays over water it is likely to encounter some vertical
shear at that time.


KEY MESSAGES:

1. Irma is a potentially catastrophic category 5 hurricane and will
bring life-threatening wind, storm surge, and rainfall hazards to
portions of the northern Leeward Islands, including the Virgin
Islands and Puerto Rico, today.  Preparations should be rushed to
completion.

2. A Hurricane Warning is in effect for the northern coast of the
Dominican Republic, as well as the southeastern Bahamas and the
Turks and Caicos, with hurricane watches for portions of Haiti and
the central Bahamas. Irma is likely to bring dangerous wind, storm
surge, and rainfall to these areas from Wednesday night through
Friday.

3. Irma could directly affect the remainder of 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. The chance of direct impacts from Irma beginning later this week
and this weekend from wind, storm surge, and rainfall continues to
increase in the Florida Keys and portions of the Florida Peninsula.
However, it is too soon to specify the timing and magnitude of these
impacts.


FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 17.9N  62.6W  160 KT 185 MPH
 12H  06/1800Z 18.6N  64.6W  155 KT 180 MPH
 24H  07/0600Z 19.6N  67.3W  150 KT 175 MPH
 36H  07/1800Z 20.6N  70.0W  145 KT 165 MPH
 48H  08/0600Z 21.3N  72.5W  140 KT 160 MPH
 72H  09/0600Z 22.5N  77.0W  135 KT 155 MPH
 96H  10/0600Z 24.0N  80.0W  125 KT 145 MPH
120H  11/0600Z 26.5N  80.9W  105 KT 120 MPH...INLAND

$$
Forecaster Beven

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Page last modified: Thursday, 14-Dec-2017 12:09:21 UTC