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Hurricane Irma Discussion Number 34
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Thu Sep 07 2017
The eye on satellite continues to be quite distinct, and data from
an Air Force reconnaissance plane indicate that the initial
intensity is 150 kt. The central pressure remains near 921 mb.
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
will not remain a powerful hurricane for the next 3 days while
approaching Florida. Thereafter, an increase in the wind shear could
lead to gradual weakening, but Irma is expected to remain a
major hurricane until landfall occurs.
The best estimate of the initial motion is toward the west-northwest
or 290 degrees at 14 kt. Irma is being steered by the flow around
the south side of the subtropical ridge, but in 2 to 3 days, the
hurricane will be located on the southwestern edge of the
aforementioned ridge, and a turn to the northwest and north-
northwest should then begin. There has been no change in the
guidance which is still quite clustered and brings the core
of Irma very near the southeast Florida coast in about 3 days.
The NHC forecast, which is similar to the previous one, is very
close to the multi-model consensus and the HFIP corrected consensus
HCCA. The later has been performing very well during Irma.
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 today. These hazards
will spread across the Turks and Caicos tonight and the Bahamas
tonight through Saturday.
2. A hurricane watch is in effect for much of Cuba. Irma is likely
to bring dangerous wind, storm surge, and rainfall to portions of
these areas on Friday and Saturday.
3. The threat of dangerous major hurricane impacts in Florida
continues to increase. A hurricane watch has been issued for south
Florida, the Florida Keys, Lake Okeechobee, and Florida Bay. This
watch will likely be expanded northward later today. Residents in
these areas should heed any advice given by local officials.
4. A storm surge watch has also been issued 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
5. The chance of direct impacts is increasing in portions of
Georgia, South Carolina, and North Carolina, but it is too early to
specify the magnitude and location of the impacts.
FORECAST POSITIONS AND MAX WINDS
INIT 07/1500Z 20.4N 69.7W 150 KT 175 MPH
12H 08/0000Z 21.1N 71.7W 145 KT 165 MPH
24H 08/1200Z 21.9N 74.2W 140 KT 160 MPH
36H 09/0000Z 22.5N 76.5W 135 KT 155 MPH
48H 09/1200Z 23.1N 78.4W 135 KT 155 MPH
72H 10/1200Z 25.5N 80.0W 125 KT 145 MPH
96H 11/1200Z 30.1N 80.6W 105 KT 120 MPH
120H 12/1200Z 35.0N 82.0W 50 KT 60 MPH...INLAND