Helene Now a Hurricane 550 Miles Across, Impacts Will Spread Far Inland
9/25/24 3PM CDT – Today, Helene intensified into a hurricane and it should become a major hurricane before making landfall tomorrow in the Big Bend area of the Florida Panhandle. Some forecasters are predicting a Category 3 storm, others a Cat 4.
Helene will accelerate to the north today and Thursday crossing the entire Gulf of Mexico in a 24-30 hour period and reach the Florida Gulf coast late Thursday, according to the National Hurricane Center (NHC).
Warm Waters Will Fuel Rapid Intensification
Harris County Meteorologist Jeff Lindner says, “Helene will be passing over extremely warm waters that extend 100-200 feet deep. That supports great levels of intensity in developing hurricanes. Nearly all the hurricane intensity models bring Helene to Category 4 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 speed break point between Categories 3 and 4 is 130 MPH.
Impacts Will Be Felt Far Inland
Regardless, all forecasters comment on the size of Helene. At 1PM, tropical storm force winds extended outward 275 miles from the center, according to NHC.
As a result, they predict Helene’s impacts will extend well inland. Tropical storm force winds will likely reach Atlanta and even the southern Appalachian Mountains.
Life-Threatening Storm Surge
But the most certain threats to life and property have to do with storm surge. Today forecasters say it could reach up to 20 feet above land; yesterday it was 15.
Jeff Lindner, Harris County’s meteorologist says, “Structures lower than 10 ft will be completely destroyed along the entire Florida nature coast. This will potentially be a record storm surge event for the eastern side of the Florida Big Bend, likely surpassing previous records from the March 1993 ‘superstorm’ surge event.”
Torrential Rain and Flash-Flood Threats
Farther inland, the threat will be torrential rains. Atlanta, which usually doesn’t experience tropical threats, could receive 8-12 inches with higher isolated totals. Areas in the mountains north of Atlanta could receive 16-20 inches.
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 northern Georgia into western North Carolina and eastern Tennessee.
In the rainfall map above, note the red and brown colored areas along the North Carolina/Tennessee border. That is a mountainous region.
The excessive rainfall there is orographic in origin. Orographic means precipitation caused by hills or mountain ranges deflecting moisture-laden air masses upward, causing them to cool and precipitate their moisture.
All that precipitation will likely trigger flash flooding.
Widespread travel disruption is likely over the southeast from Thursday into Saturday. Recovery of essential services will be slow due to the widespread, significant impacts.
Key Messages
The NHC warns:
- Due to the large size of Helene, there is a danger of life-threatening storm surge along the entire west coast of the Florida Peninsula and Florida Big Bend. Residents should follow the evacuation advice of local officials.
- Devastating hurricane-force winds will reach from northern Florida into southern Georgia. Because of Helene’s expected fast forward speed, damaging and life-threatening wind gusts are expected to penetrate well inland to the southern Appalachians.
- Helene will bring heavy rain and potentially life-threatening flash and urban flooding. Impacts will stretch across portions of northwestern and northern Florida, the Southeast, southern Appalachians, and the Upper Tennessee Valley Wednesday through Friday.
- Widespread minor to moderate river flooding is likely, and isolated major river flooding is possible.
Types of Damage Associated with Category 4 Hurricanes
The National Weather Service lists types of damage typically associated with a Category 4 Hurricane. “Winds 130-156 mph. Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.”
Sounds a lot like Beryl.
Posted by Bob Rehak on 9/25/24
2584 Days since Hurricane Harvey
