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Tropical Storm Irma Discussion Number  51
NWS National Hurricane Center Miami FL       AL112017
500 PM EDT Mon Sep 11 2017

Surface synoptic data over the southeastern United States indicate
that Irma continues to weaken.  The maximum winds are now near 45
kt, and these are confined to the Georgia and South Carolina coastal
area, along with some winds to tropical storm force in interior
central to northern Georgia. Irma continues to have some
extratropical characteristics, since a fairly well-defined
baroclinic zone lies not far from the center. Nevertheless, the
large circulation should continue to spin down due to land
interaction and strong southwesterly shear. The official intensity
forecast is above most of the guidance, so the system could weaken
faster than shown here. Irma should weaken to a depression in 24
hours or sooner, and the global guidance shows the circulation
dissipating over the east-central United States after 48 hours.

Synoptic center fixes give a continued north-northwestward motion
of 340/15 kt.  There is little change to the track forecast
reasoning.  For the next day or two, Irma or its remnants should
move on a north-northwestward to northwestward track along the
periphery of a broad mid-level cyclonic gyre.  The official
forecast is a blend of the latest GFS and ECMWF solutions.

KEY MESSAGES:

1. There is the danger of life-threatening storm surge flooding
along portions of the coasts of western Florida, Georgia, and South
Carolina, where Storm Surge Warnings remain in effect.

2. Irma is producing very heavy rain across the southeastern United
States.  Intense rainfall rates are leading to flash flooding and
rapid rises on creeks, streams, and rivers.  Significant river
flooding will persist over the Florida peninsula in the wake of Irma
and in Georgia, South Carolina and north-central Alabama, where
additional heavy rains are expected.  Portions of these states
within the southern Appalachians will be especially vulnerable to
flash flooding.  Irma is also expected to produce heavy rains in
northern Mississippi and southern portions of Tennessee and North
Carolina, where local flooding may occur.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 31.5N  84.0W   45 KT  50 MPH...INLAND
 12H  12/0600Z 33.1N  85.5W   35 KT  40 MPH...INLAND
 24H  12/1800Z 34.5N  87.3W   30 KT  35 MPH...INLAND
 36H  13/0600Z 35.8N  88.8W   25 KT  30 MPH...POST-TROP/INLAND
 48H  13/1800Z 37.0N  88.5W   20 KT  25 MPH...POST-TROP/INLAND
 72H  14/1800Z...DISSIPATED

$$
Forecaster Pasch

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