Florence Goes West – Destination Southern Appalachian Mountains

As of 9/13/2018 the forecasts indicate that Hurricane Florence will be in direct course to hit the Southern Appalachians and then veer North following  and possibly crossing over the mountains[1].    As the storm approaches the mountains, interactions with topography will begin to impact the storm path along with strong enhancement of precipitation due to orographic effects.  Despite landfall in Florida, the highest amount of rainfall produced by Frances anywhere in the continental US was recorded at Mount Mitchell, and in the case of Ivan also in 2004, the highest rainfall amount was registered further south along the eastern slopes of the Southern Appalachians triggering landslides and debris flows such as the deadly Peeks Creek in Macon County.  Although Florence’s evolution has been different than Frances, Ivan and other historical storms, and the predicted track and storm intensity can still change significantly after landfall,  our understanding of orographic enhancement processes and fundamental lessons learned from past research[2]tell us that given the current outlook, it is reasonable to expect that sustained precipitation intensities on the order of 3-4’’ (75-100 mm/hr) could develop over ridges on the eastern flanks of the Southern Appalachians producing 24-hr-48hr rainfall accumulations  producing more than 1ft of rainfall at local places[3].   Thus, even as all eyes are on the Coastal Plain in anticipation of Florence’s landfall and we know already of the great damage that it will impose on Eastern North Carolina communities, economy and ecosystems, it is important to prepare for potential impacts in Western North Carolina in the next week or so with strong warnings for life-threatening flash floods and landslides if Florence moves as currently forecasted.   

[1]https://cera.coastalrisk.live/

[2]Brun and Barros, 2012: //doi.org/10.1080/01431161.2012.714088;Sun and Barros, 2012: //doi.org/10.1175/MWR-D-11-00345.1; Tao and Barros, 2013: //doi.org/10.1016/j.jhydrol.2013.02.052; Brun and Barros, 2013: //doi.org/10.1002/joc.3703; Brun and Barros, 2014: //doi.org/10.1002/qj.2255; Tao and Barros, 2014: //doi:10.5194/hess-18-367-2014.

[3]Actual rainfall on the ground in the mountains being twice as high as that that can be reliable monitored by the national radar network.