5 October 2015
Make no mistake, this was a flood event unlike any other in South Carolina and while Hurricane Joaquin never hit the coast, it holds a smoking gun. This flood was the result of several factors, an upper level low over the Southeast U.S. along with a large Canadian High over Eastern Canada, and climate change is in the mix as well since the oceans over this region (and globally) were at record warmth.
All of this played a role.
The upper level low helped to aim a fire-hose of deep tropical moisture into South Carolina and this resulted in rainfall totals that had never before been measured there. The moisture was in part from the Hurricane and also from a previous river of moist air that extended from the Tropical Pacific (where El Nino is at near record levels) and another stream of wet air from the western Caribbean as well. You can see this fire hose of moisture on the IR Water vapor wavelength satellite loop below (Hat tip to the CIMMS Satellite folks for posting this GOES Water Vapor wave length imagery, click to see the animation, but be warned it is a big file and will take a minute to load.):
There is a good perspective piece by Chris Mooney today in the Washington Post that is well worth a read. Dr. Jeff Halverson has a detailed look at the synoptic meteorology behind this event at Capital Weather Gang as well.
So how bad was it? Look at the rainfall data below, from the NWS in Columbia SC, where daily rainfall records began in June of 1887:
Some folks on social media today were saying that calling this a 1000 year flood event is ridiculous since we do not have rainfall records for a thousand years. These people are wrong (and suffering from the Dunning-Kruger Effect as well), Dr. Marshal Shepherd past President of the AMS has a good explainer here. I’ve said it before, and I’ll say it again, we should REQUIRE a course in statistics to get a high school diploma.