A fake, a firehose, a record rain: SC October Floods 2015, Part I

Hurricane Joaquin Track

It was big. We have already forgotten how big it was.

Hurricane Joaquin was a massive Category 4 hurricane with 135-knot winds, 500 miles off the coast. At one point, it was just 2 mph shy of becoming a Category 5 hurricane. Where was it heading? At one point, it was predicted to make landfall. It was not until later in the week that models converged on a track away from land.

Hurricane Joaquin Track
Picture…Hurricane Joaquin in the Atlantic Ocean north of Bermuda at 1315Z on October 5, 2015. GOES East satellite image from NOAA EVL

Like a direct snap to a wide receiver, where the quarterback sneaks away to catch the ball in the end zone, Hurricane Joaquin was a fake-a trick play. While all eyes were on the hurricane, the real action was a low-pressure system forming over the Southeast that kept Joaquin away but brought something worse.

This system pulled moist tropical air from Hurricane Joaquin to create a meteorological equivalent of a firehose pointed directly towards South Carolina. Washington Post’s Capital Weather Gang wrote the best article on how the Xs and Os all lined up to produce this historic event.

As of Thursday, October 2, forecasters were not predicting radical rain in South Carolina. Here was the estimate produced on Thursday. This changed dramatically on Friday when I started to hear the word “historic” rainfall for the first time.

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So how much rain fell? Here are the totals.

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Rainfall totals from this event blew away the records in South Carolina.

  • The official statewide 24-hour rainfall record was exceeded in several locations. For South Carolina, the standing 24-hour precipitation record was set during Hurricane Floyd when 14.80 inches of rain fell in Myrtle Beach on Sept. 16, 1999. One rainfall record example was Gills Creek in Columbia where 16.61 inches of rain between midnight and 10 p.m. Oct. 4 (National Weather Service).
  • The unofficial state record for 5-day total rainfall, which had stood for 107 years, has been surpassed at more than a dozen reporting sites.
  • The rainfall exceeded that of any tropical cyclone in South Carolina history (Source).
  • The October monthly precipitation record for any location in the state has likely been broken.
  • (I’ll probably keep editing this list)

Many were calling this a 1,000-year storm event. I did check, and sure enough, many of the precipitation totals exceeded 1,000 average recurrence interval. Standard disclaimer when talking about recurrence intervals: Many scientists believe the term is misleading as, in most cases, only a hundred years of data is available to make predictions.

1000 YEAR TWITTER

According to some estimates, North Carolina received 5.2 trillion gallons and South Carolina 5.8 trillion gallons which would be enough to fill 636 million swimming pools or end the drought in parts of California. I am not going to try to check those numbers.

My next post I’ll summarize on our rivers response to this rain. Part II of a series of posts about the October SC 2015 Flood