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Hurricane Irma Discussion Number 35
NWS National Hurricane Center Miami FL AL112017
500 PM EDT Thu Sep 07 2017

Hurricane Irma continues to have an impressive satellite
presentation with a very distinct eye. There is not much more to add
about the current intensity except that numerous data from the Air
Force reconnaissance plane indicate that the winds remain at 150
kt.

The environment along the future track of Irma is favorable for the
hurricane to maintain most of its current intensity, although some
fluctuations are likely due to eyewall replacement cycles which are
difficult to predict. There are no obvious reasons why Irma should
not remain a powerful major hurricane for the next 3 days while it
is heading for Florida or its adjacent surroundings. Thereafter, an
increase in the wind shear and the interaction with land should lead
to gradual weakening.

The best estimate of the initial motion is toward the west-northwest
or 285 degrees at 14 kt. Irma is being steered by the flow around
the south side of the subtropical ridge, but in 2 or 3 days the
hurricane is expected to be located on the southwestern edge of the
aforementioned ridge, and a turn to the northwest and north-
northwest should then begin. The forecast track for the first 2 days
was adjusted a little bit to the south given that the ridge to the
north continues to be strong, and the ECMWF and HFIP corrected
consensus (HCCA) models have shifted southward a little bit. These
two models have been performing very well during Irma. This
adjustment also results in a westward shift of the track near
Florida and northward.

KEY MESSAGES:

1. Irma is a potentially catastrophic category 5 hurricane and will
continue to bring life-threatening wind, storm surge, and rainfall
hazards to the northern coast of Hispaniola tonight. These hazards
are already spreading across the Turks and Caicos and will affect
the Bahamas tonight through Saturday. Hurricane conditions will also
spread over portions of the north coast of Cuba, especially over
the adjacent Cuban Keys through Saturday.

2. It has become more likely that Irma will make landfall in
southern Florida as a dangerous major hurricane, and bring
life-threatening storm surge and wind impacts to much of the state.
A Hurricane Watch is in effect for South Florida, the Florida Keys,
Lake Okeechobee, and Florida Bay, and will likely be expanded
northward tonight.

3. A Storm Surge Watch is in effect for portions of South Florida
and the Florida Keys. This means there is the possibility of
life-threatening inundation from rising water moving inland from the
coastline during the next 48 hours in these areas. The Potential
Storm Surge Flooding Map depicts a reasonable worst-case scenario -
the amount of inundation that has a 10 percent chance of being
exceeded. Because the Flooding Map is based on inputs that extend
through 72 hours, it best represents the flooding potential in the
watch area.

4. There is a chance of direct impacts in portions of Georgia,
South Carolina, and North Carolina, but it is too early to specify
the magnitude and location of these impacts.

FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 20.9N 71.1W 150 KT 175 MPH
12H 08/0600Z 21.6N 73.1W 145 KT 165 MPH
24H 08/1800Z 22.2N 75.5W 140 KT 160 MPH
36H 09/0600Z 22.7N 77.6W 135 KT 155 MPH
48H 09/1800Z 23.4N 79.3W 135 KT 155 MPH
72H 10/1800Z 26.2N 80.7W 115 KT 130 MPH...INLAND
96H 11/1800Z 31.5N 82.0W 80 KT 90 MPH...INLAND
120H 12/1800Z 36.0N 84.0W 40 KT 45 MPH...INLAND