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ORLANDO, Fla. - Hurricane Helene unleashed extreme rainfall on the Blue Ridge Mountains of North Carolina and Tennessee, dumping 15–30 inches of rain and causing widespread destruction.
The storm transported three times the water vapor of the West Coast’s most intense atmospheric river events, delivering an estimated 3,000 Integrated Vapor Transport (IVT) units of moisture in just two days, according to meteorologist Dr. Ryan Maue.
This massive water vapor transport, which outpaced the region’s historic 1916 flood by approximately 1,000 IVT units, is unprecedented in modern U.S. meteorological history. Ben Noll, of New Zealand’s National Institute of Water and Atmospheric Research, suggested Helene's vapor transport may rival the most extreme events ever recorded globally.
Hurricanes act as a heat transfer mechanism, moving heat energy from the warm southern latitudes, where it's stored in water vapor, to cooler northern areas.
"A primary function of hurricanes is to transport heat energy absorbed into clouds to the higher latitudes, to equalize heat distribution on our planet. The heat is initially gained along the southern latitudes by the sharper sun angle that is present near the equator, and tropical systems push that heat to areas that are cooler, farther north," explained FOX 35 Storm Team Chief Meteorologist Brooks Garner.
Garner said that heat is stored much like how you would ship an item in a box.
"Its 'box' being the inside of molecules of water vapor, formed from evaporated warm ocean water," he added. "The heat energy stored is called, 'latent heat,' The stronger the heat content – which this season is extreme over the oceans – the more water vapor can be evaporated into the atmosphere to be 'shipped' north."
This season’s extreme ocean heat increased the amount of water vapor Helene carried north. As the storm approached the Blue Ridge Mountains, a process called orographic lifting forced the clouds upslope, squeezing out torrential rain in record amounts.
While Florida was spared Helene’s heaviest rains, the Gulf Coast endured a devastating storm surge, particularly from Tampa Bay to the Big Bend communities of Cedar Key and Horseshoe Beach.