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Hurricane Irma Discussion Number 46
NWS National Hurricane Center Miami FL AL112017
1100 AM EDT Sun Sep 10 2017
Latest observations from the Air Force Hurricane Hunters had
flight-level winds that corresponded to surface winds near 110 kt.
Thus, given sampling considerations, the 115-kt intensity is
retained for this advisory. Irma should maintain this intensity
until the center reaches the southwest Florida coast, and then begin
to weaken while the system interacts with the landmass of the
Florida peninsula. Increasing southwesterly shear associated with
an upper-level trough should also cause weakening of the hurricane
during the next day or so. More rapid weakening is likely after Irma
moves into the southeastern United States in 24-36 hours, and the
cyclone should weaken to a remnant low in 72 hours or sooner. The
official intensity forecast is close to the simple and corrected
consensus models.
The center of Irma wobbled more northward over the past few hours
and the initial motion estimate is about 350/8 kt. Irma is embedded
within a broad mid-level gyre over the Gulf of Mexico. The cyclone
is expected to be steered north-northwestward at a faster forward
speed over the next day or two on the eastern side of the gyre. This
will take Irma inland over northern Florida early on Monday and the
southeastern United States over the next couple of days. The track
guidance remains fairly tightly clustered with the ECMWF track a
little to the left and slower than the other models. The official
track forecast lies between the model consensus and the ECMWF
solution. This is just slightly east of the previous official
forecast.
KEY MESSAGES:
1. Life-threatening wind and storm surge from Irma will continue in
the Florida Keys and southwestern Florida today and spread into
central and northwestern Florida tonight and Monday. Preparations
in central and northwestern Florida should be rushed to completion.
2. There is imminent danger of life-threatening storm surge flooding
along much of the Florida west coast, including the Florida Keys,
where a Storm Surge Warning is in effect. The threat of
catastrophic storm surge flooding is highest along the southwest
coast of Florida, where 10 to 15 feet of inundation above ground
level is expected. This is a life-threatening situation.
3. Irma will bring life-threatening wind impacts to much of Florida
regardless of the exact track of the center. Wind hazards from Irma
are also expected to spread northward through Georgia and into
portions of Alabama, Tennessee, South Carolina, and North Carolina.
4. Irma is expected to produce very heavy rain and inland flooding
across much of Florida and many other parts of the southeast United
States. Rainfall occurring very quickly, at 2 to 4 inches per hour,
will lead to flash flooding and rapid rises on creeks, streams, and
rivers. Significant river flooding is likely over the next five
days in the Florida peninsula and southeast Georgia, where average
rainfall of 8 to 15 inches and isolated 20 inch amounts are
expected. Significant river flooding is also possible beginning
Monday and Tuesday in much of eastern and central Georgia, western
South Carolina, and western North Carolina, where average rainfall
of 3 to 8 inches and isolated 12 inch amounts are expected.
Mountainous parts of these states will be especially vulnerable to
flash flooding. Farther west, Irma is expected to produce average
amounts of 2 to 5 inches in parts of Alabama and Tennessee, where
isolated higher amounts and local flooding may occur.
FORECAST POSITIONS AND MAX WINDS
INIT 10/1500Z 25.0N 81.5W 115 KT 130 MPH
12H 11/0000Z 26.6N 82.1W 110 KT 125 MPH
24H 11/1200Z 29.2N 83.0W 80 KT 90 MPH
36H 12/0000Z 31.9N 84.6W 40 KT 45 MPH...INLAND
48H 12/1200Z 33.8N 86.7W 30 KT 35 MPH...INLAND
72H 13/1200Z 36.0N 89.0W 25 KT 30 MPH...POST-TROP/INLAND
96H 14/1200Z 38.5N 86.5W 20 KT 25 MPH...POST-TROP/INLAND
120H 15/1200Z...DISSIPATED
$$
Forecaster Pasch
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