Severe Weather in September

 

Tornadoes spawned by Ivan's remnants, September 2004 (Source: NOAA)

Severe weather is defined as a thunderstorm that contains any of the following: wind gusts of at least 58 mph, hail 1”/+ in diameter, or a tornado.  Although less common than during the spring and early summer, severe weather does occur in September.  The remnants of tropical storms and hurricanes can also be a significant contributor to severe weather during September. 

2020: A small but significant severe weather outbreak occurred in the D.C. Metro Area on September 3.  Several reports of severe wind gusts were reported with a variety of damage that ranged from downed trees and power lines to roof damage.  An EF-1 tornado also developed in Anne Arundel Co., Maryland and tracked over six miles according to NOAA.  

2018: Hurricane Florence made landfall on September 14 and its remnants lingered for several days and brought devastating flooding and severe weather to the Mid-Atlantic Region.  The D.C. Metro Area felt significant impacts on September 17-18, with 13 confirmed tornadoes in Virginia alone.  The strongest was an EF-2 tornado on the Enhanced Fujita Scale with wind speeds of 115-125 mph.  A record rainfall total of 2.22” occurred at BWI Airport on September 18.

2004: Once a Category 5, Ivan made landfall as a Category 3 on the U.S. Gulf Coast on September 16.  It had far-reaching impacts, including in the Mid-Atlantic Region where its remnants produced a tornado outbreak on September 17, 2004.  According to NOAA, Ivan was the top tornado producing hurricane on record with a total of 127 tornadoes in the United States.  (Hurricane Beulah had been the previous record-holder with 115 confirmed tornadoes in 1967.)  Dulles Airport had a rainfall record of 1.71” on September 17 from the remnants of Ivan. 

2001: September 24 will be the 21^st anniversary of the deadly F3 College Park tornado that claimed the lives of two sisters who were caught in their car on the campus of the University of Maryland.  At peak intensity, the tornado had winds of nearly 200 mph.  Although it was ranked an F3 at the time, the College Park tornado would be a borderline EF4/EF5 tornado today.  The College Park tornado was one of several, including an F4 in Culpeper Co., Virginia that touched down in the D.C. Metro Area.  

High Impact Tropical Systems in D.C.

 

Hurricane Isabel, September 2003  (Source: NOAA)

September is the most active month of the Atlantic hurricane season because atmospheric and environmental conditions tend to be the most favorable.  Although less common than along the Gulf or Southeast coasts of the United States, the D.C. Metro Area has felt the brunt of decaying tropical systems during September.

Hurricane Florence (2018): A Cape Verde hurricane that lasted more than two weeks, Florence was a Category 4 at peak intensity over the open Atlantic.  It had sustained winds of 150 mph and a minimum central air pressure of 937 millibars (mb).  Fortunately, it weakened to Category 1 intensity before its landfall in North Carolina on September 14.  However, because the atmospheric steering currents were weak, it meandered across the Carolinas and Mid-Atlantic Region for several days and caused devastating flooding/severe weather.  BWI Airport had a rainfall record of 2.22” on September 18.

Hurricane Ivan (2004): Once a Category 5, Ivan made landfall as a Category 3 on the U.S. Gulf Coast on September 16.  It had far-reaching impacts, including in the Mid-Atlantic Region where its remnants produced a tornado outbreak on September 17, 2004.  According to NOAA, Ivan was the top tornado producing hurricane on record with a total of 127 tornadoes in the United States.  Dulles Airport had a rainfall record of 1.71” on September 17 from the remnants of Ivan.  

Hurricane Isabel (2003): Hurricane Isabel made landfall in North Carolina on September 18 as a Category 2 storm.  That was considerably weaker than its peak intensity as a Category 5 hurricane over the open Atlantic with sustained winds of 165 mph.  As Isabel continued to weaken, it tracked west of Washington, D.C. and caused heavy rain and gusty winds in the D.C. Metro Region. 

Over one million power outages were observed around the Nation’s Capital, in addition to record rainfall at both National (2.28”) and Dulles Airports (1.76”) on September 18.  Significant coastal flooding occurred in Old Town Alexandria, Virginia and in Annapolis, Maryland.   The highest tide in Annapolis reached 7.58 feet above normal, breaking the 1933 hurricane record.  Flooding from Isabel occurred in Georgetown with flood stage that reached 11.3 feet above normal, which broke the 1933 hurricane surge record. 

Hurricane Floyd (1999): Floyd was the most intense hurricane of the 1999 season as a strong Category 4 hurricane with peak sustained winds of 155 mph and a minimum central air pressure of 921 mb.  Fortunately, Floyd weakened to a Category 2 storm before its landfall on September 16 near Cape Fear, North Carolina.  Floyd was exceptionally large in diameter so its effects were far-reaching.  

As Floyd continued its northward trek, it brought heavy rainfall, damaging winds, and coastal flooding.  Widespread flooding also occurred in the D.C. Metro Region with higher rainfall totals on the east side of town.  Daily rainfall records were set on September 16 at both Dulles (2.05”) and BWI Airports (5.02”).