Remembering the Twin Dangers of Hurricanes Dennis and Floyd

Hurricane Floyd making landfall in North Carolina (Source: NOAA)

The summer of 1999 was exceptionally hot across the Mid-Atlantic Region.  There were three days of triple digit heat and 45 days of 90 degree heat.  The summer months were also exceptionally dry.  The lack of rainfall in conjunction with the extreme heat created tough conditions for farming and gardening.  However, by the time September 1999 arrived, the tropics began to get active.

Early that September, the remnants of Hurricane Dennis brought the Nation’s Capital appreciable rainfall.  Over a three-day period ending September 6, nearly 2” of rain fell at both National and Dulles Airports.  That was less than two weeks after nearly 5” fell at Dulles Airport over a five-day period ending August 27.  Since the rest of the summer was so hot and dry, so much rain over a relatively short period of time did not produce widespread flooding.  It just helped replenish the moisture content of the soil and fill up local reservoirs.

Little did Washingtonians realize when Floyd became a Tropical Storm on September 8 that major flooding would ensue when the remnants of Hurricane Floyd arrived the following week.  On September 15-16, 1999, National Airport got 3.67” and Dulles Airport recorded 2.56” of rain from the remnants of Floyd.  So in less than a month, there were two significant, multi-day rainfall events.  Since the ground was already saturated after the remnants of Hurricane Dennis passed through earlier in the month, Floyd’s rains caused extensive flooding across the Mid-Atlantic Region and Northeastern United States.

Thanks to Dennis and Floyd, September 1999 catapulted into the Top 5 for wettest Septembers in the Nation’s Capital, with a monthly total of 10.27”.  By comparison, average September rainfall is only 3.31” and the driest September on record in Washington, D.C. was in 2005 when just 0.11” of rain fell.

This post is filed from Lisbon, Portugal, where I've been researching some local weather issues that will be the subject of an upcoming blog post.