Hurricane Irma Discussion Number 43 NWS National Hurricane Center Miami FL AL112017 500 PM EDT Sat Sep 09 2017
Data from a NOAA Hurricane Hunter plane sampling Irma indicate that the hurricane has not recovered yet from its interaction with Cuba. It is estimated that the maximum winds are 110 kt. Given the excellent satellite presentation, the lower pressure just reported by the NOAA plane, and the fact that the hurricane will move over the warm waters of the Straits of Florida, some intensification is anticipated during the next 24 hours. Irma is expected to remain a very dangerous hurricane while it moves near or over the Florida Keys and near or over the Florida Peninsula. After 48 hours, Irma will be moving farther inland and weakening.
Radar data indicate that Irma is moving toward the west-northwest at about 8 kt. The turn toward the northwest and north-northwest is about to begin since the hurricane is already at the western edge of the subtropical ridge. The track guidance continues to be tightly packed, and the bulk of the models take the hurricane over the Florida Keys and near or over the Florida Peninsula. The NHC forecast is in the middle of the guidance envelope, and given the good agreement among models, the confidence in the track forecast is high.
KEY MESSAGES:
1. Irma is expected bring life-threatening wind and storm surge to the Florida Keys and southwestern Florida as an extremely dangerous major hurricane tonight through Saturday. Preparations in southwest Florida should be completed within the next few hours, as tropical-storm-force winds are expected to begin tonight.
2. There is an imminent danger of life-threatening storm surge flooding in portions of central and southern Florida, 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, and everyone in these areas should immediately follow any evacuation instructions from local officials.
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 much of Georgia and portions of South Carolina and Alabama.
4. Irma is expected to produce very heavy rain and inland flooding. Total rain accumulations of 10 to 20 inches, with isolated amounts of between 20 and 25 inches, are expected over the Florida Keys, the Florida peninsula, and southeast Georgia from Saturday through Monday. Significant river flooding is possible in these areas. Early next week Irma will also bring periods of heavy rain to much of the southeast United States where an average of 2 to 6 inches is forecast, with isolated higher amounts, from North and South Carolina to Tennessee and eastern Alabama. This includes some mountainous areas which are more prone to flash flooding. Residents throughout the southeast states should remain aware of the flood threat and stay tuned to forecasts and warnings.