Helene wreaks havoc across Southeast, killing at least 42

Chart: Category 4 hurricanes are intensifying fasterJoe MurphyHelene took about 31 hours to intensify from a Category 1 hurricane to a Category 4, and in the recorded history of Atlantic basin hurricanes, that’s pretty fast.The length of time it takes Category 4 hurricanesto intensify has shortened in recent years, according to an NBC News analysis of National Oceanic and Atmospheric Administration data.Since 2015, an average Category 4 hurricane —those with wind speeds of 130 mph to 156 mph —has taken 42 hours to intensify from a Category 1. Thirty years earlier, that figure was 52 hours.Evacuation orders issued for areas downstream of Nolichucky DamJoe KottkeEvacuations are in progress in areas that could be impacted if there is a breach of Tennessee's Nolichucky Dam. A flash flooding warning for dam failure has been issued for the area downstream of the dam, including north central Cocke County, southwestern Green County and southeastern Hamblen County. Cooke County Mayor Rob Mathis...