Flash Flooding in Bermuda


Typically, Bermuda can expect to see a flash flooding situation maybe once a year because of extreme rainfall rates and high tides. However, this year has seen three flash flooding situations. Interestingly enough, since 2007, there has been a notable amount of heavy rainfall events per year. Whats even more bizarre is that many of them occur during dry periods that have become increasingly frequent.

The chances of a heavy rainfall event lining up with a high tide cycle is very low so to see so many such alignments in one yearis unusual. The key is that some low lying areas are less than 5 feet above sea level, so heavy rain draining from roadways etc down into these valleys essentially collects in a bowl. At high tide, or during a rising tide, this water cannot drain into the water table as efficiently (or out through the canal in Pembroke) and flooding occurs. For more than an inch of rain to occur in a day, a slow moving front must be able to tap into a tropical moisture feed; or a slow moving tropical cyclone moves nearby. The mechanisms that allow heavy rain to fall also can produce severe winds and so flooding (which is usually minor and isolated to areas that typically flood) takes a back seat. Perhaps an increase in urbanization combined with the slight rise in sea level is making flash flooding events more frequent in Bermuda, but this is hard to prove. Below is a chronicle of the >1″ of rain in a day events since 2007.

2007 – 15 heavy rainfall events
January 25th – 1.12″
February 16th – 1.01″
March 17th – 1.43″
April 6th – 1.70″ (flooding)
May 14th – 2.69″ (flooding)
May 29th – 1.73″
June 9th – 1.11″
June 26th – 1.40″
July 24th – 1.32″
July 25th – 1.60″
July 31st – 1.28″
August 4th – 1.47″
August 31st – 1.14″
October 12th – 1.74″
November 3rd – 1.18″
2008 – 12 heavy rain events
March 23rd – 1.89″
March 24th – 2.16″
April 15th – 1.25″
April 21st – 1.43″
April 23rd – 1.02″
May 3rd – 1.99″
May 6th – 2.63″ (flooding)
May 12th – 2.92″ (flooding)
July 14th – 4.63″ (Tropical Storm Bertha)
September 28th – 1.32″ (Tropical Storm Kyle)
October 6th – 2.60″
December 13th – 2.52″
2009 – 10 heavy rainfall events
February 16th – 1.04″ (Accompanying Severe Weather)
June 9th – 1.16″
June 16th – 1.04″
June 23rd – 1.24″
June 24th – 2.37″
June 25th – 1.39″
September 13th – 1.54″
October 1st – 1.29″ (flooding)
October 13th – 2.56″ (Accompanying Severe Weather)
October 19th – 1.19″
2010 – 8 heavy rainfall events
July 2nd – 1.43″
July 29th – 1.31″
July 31st – 1.20″
August 21st – 1.24″
September 9th – 1.72″
September 10th – 1.27″
September 19th – 2.87″ (Hurricane Igor)
October 21st – 1.78″
2011 – 9 Heavy rainfall events
January 19th – 1.24″
April 6th – 1.23″
July 18th – 1.75″
July 19th – 1.16″
August 2nd – 1.26″
August 23rd – 1.06″
September 17th – 1.30″
October 4th – 2.05″
November 30th – 1.51″
2012 – 7 Heavy rainfall events (so far…)
January 3rd – 1.03″
May 11th – 1.68″
May 22nd – 1.30″ (precursor complex to Tropical Storm Beryl)
June 15th – 2.59″ (flooding)
August 16th – 2.06″
September 9th – 4.20″ (Tropical Storm Leslie)
September 14th – 2.19″ (Flooding and Severe thunderstorms)

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