Powerful hurricane will bring devastating impacts to portions of FL and the SE US.
Discussion:
Helene has become much better organized over the last 24 hours with the central pressure recorded by the most recent USAF mission down to 979mb with sustained winds of 70mph. A large mass of deep convection has developed over the center of the tropical storm with increasing outflow to the northeast. Helene has turned toward the NW and will pass very near the NE tip of the Yucatan this morning. The wind field has continued to grow in size with tropical storm force winds extending outward 175 miles from the center.
Track:
Helene is starting to northward turn and there has been little change in the forecast track reasoning as Helene will move northward over the eastern Gulf of Mexico between a ridge of high pressure east of FL and toward an area of upper level low pressure over the mid MS valley. Helene will accelerate to the north today and Thursday crossing the entire Gulf of Mexico in a 24-30 hour period and reach the FL Gulf coast late Thursday. Track confidence is high and there is good agreement among the various track consensus aides. On this track a significant hurricane event will occur in the Big Bend portion on FL on Thursday.
Given the fast forward speed and large diameter of the wind field at and post landfall (20-25mph), powerful damaging winds will extend unusually far inland across portions of the SE US and much of the state of FL. Sustained hurricane force winds are likely to reach over 100 miles inland and sustained tropical storm force winds potentially into northern GA including the Atlanta metro area.
Intensity:
It appears Helene is in the process of closing off an inner core structure and once this is complete there is little to prevent significant intensification of this system. A well defined outflow channel to the north of Helene is in place and this will help to evacuate mass out of the center of the developing eye later today into Thursday. Helene will be passing over extremely warm waters that extend 100-200 feet deep which has been shown to support great levels of intensity in developing hurricanes. Nearly all the hurricane intensity models bring Helene to category 4 intensity over the eastern Gulf of Mexico. The official forecast is for a 120mph category 3, but this may need to be adjusted upward given current trends and guidance.
The wind field will greatly expand across the Gulf of Mexico with Helene expected to be within the 90th percentile of the largest hurricanes with respect to wind radius in the eastern Gulf of Mexico. Impacts will be significant well away from the center and landfall point.
Impacts:
Life threatening storm surge values of 10-15ft will occur near and to the right of where the center crosses the coast over much of the FL Big Bend area. Storm surge values of 5-8 ft are likely in the metro Tampa Bay area. Structures lower than 10 ft will be completely destroyed along the entire FL nature coast. This is potentially going to be a record storm surge event for the eastern side of the FL Big Bend likely surpassing previous records from the March 1993 “superstorm” surge event.
Forecasted reasonable worst case storm surge values
Damaging winds are likely over much of the FL Big Bend area including the metro Tallahassee region with a large area of tropical storm conditions from the FL Keys up the entire state of FL into the Carolinas and over much of GA. Damaging winds resulting on downed trees and power outages will extend hundreds of miles inland along the track of Helene into N GA, W NC, and E TN.
Probability of sustained 40mph winds
A potentially catastrophic inland flash flood event is becoming increasingly likely as Helene interacts with a stalled frontal boundary and the higher terrain of the southern Appalachian mountains from N GA into W NC and E TN. Rainfall of 8-16 inches will be possible in this region including the metro Atlanta area which will produce devastating flooding.
Forecasted rainfall…significant inland flash flood risk will evolve over N GA into W NC and W SC
Widespread travel disruption is likely over the SE US Thursday into Saturday and recovery of essential services will be slow due to the widespread of significant impacts.
