Weather Quiz

 

Prior to this September, when was the last time Washington, D.C. experienced a cooler and wetter than average September ?

 

A.  2009

B.  2006

C.  2003

D.  1999

A Cool and Wet September

 

September 2020 is poised to finish both cooler and wetter than average in the Nation’s Capital for the first time since 2006.  Through yesterday, DC’s average monthly temperature was 1.1° below average.  While temperatures today will be warmer than average with highs in the low 80s in the DC Metro Area, a major shift in the weather pattern is on tap as the week progresses.

The first half of September was warmer than average with only five cooler than average days through September 15.  But, the second half of the month couldn’t have been more different.  Temperatures were below average on eight consecutive days through September 22 and yesterday was DC’s first warmer than average day since September 11.  NOAA’s Climate Prediction Center expects much of the next two weeks – through October 11 – to be cooler than average in the DC Metro Area.

That’s in stark contrast to last fall when Washingtonians not only experienced the third warmest September on record, but also the warmest October temperature. The high of 98° on October 2, 2019 was DC’s hottest overall October temperature on record.  While September 2019 had nine days of 90° heat, there have been only two such days this month.  That would be DC’s fewest number of 90° September days since there weren’t any in 2011.

September has also been quite wet in the DC Metro Area, with measurable rainfall on 10 of the first 27 days of the month for a total of 5.22”.  Washingtonians have experienced some weather whiplash during the month of September in recent years.  September 2018 finished as DC’s fifth wettest with 9.73”, while last September was DC’s fourth driest with only 0.25”.

Rainfall in the late summer and fall in the Nation’s Capital can vary quite a bit depending on whether any tropical systems are present.  Some DC residents may recall the record rainfall in late October 2012 due to former Hurricane Sandy.  That helps illustrate that significant rainfall can occur well into the fall season.  Fortunately, nothing is currently brewing in the tropics during what has been a very active season. 

September 10 was DC’s rainiest day of the month with a daily record of 2.88”, while this month’s hottest temperature (91°) occurred on both September 3-4.  September’s coolest temperature of 46° occurred on September 20.

2020’s Active Atlantic Hurricane Season

 

When Tropical Storm Vicky developed on September 14, it became the 20^th named Atlantic storm of the 2020 hurricane season.  That tied this season with 1933 for being the second busiest one.  Merely four days later on September 18, a total of three storms – Wilfred, Alpha and Beta – were named and that broke the tie making the 2020 Atlantic hurricane season the stand-alone second busiest on record behind 2005. 

According to Colorado State University scientist, Dr. Philip Klotzbach, it was only the second time on record that three named storms formed on the same calendar day – and first since August 15, 1893.  As of yesterday, there has been a total of 23 tropical storms, of which eight became hurricanes, including two major hurricanes.  An “average” Atlantic hurricane seasons has 12 tropical storms of which 6 become hurricanes with 3 major hurricanes.

There are some key differences between 2005 and 2020.  For example, there were five major hurricanes by this point in the 2005 hurricane season – Dennis, Emily, Katrina, Nate and Rita.  By comparison, only Hurricanes Laura and Teddy have been major hurricanes so far this season.  They were each Category 4 storms at peak intensity.  A “major” hurricane is defined as Category 3 or higher on the Saffir-Simpson Hurricane Wind Scale.

This season got off to a faster start than 2005 since two tropical storms developed in May 2020, which was prior to the official start of the hurricane season on June 1.  That made this season the sixth consecutive year at least one named storm has developed prior to June 1.  By comparison, the first named storm of the 2005 season didn’t develop until June 8.

While there has been a higher overall number of storms so far in 2020 compared to the same point of the 2005 season, there were more major hurricanes in 2005.  However, there have been more landfalling tropical systems so far this season.  When Tropical Storm Beta made landfall in Texas on September 22, it became the ninth landfalling tropical storm or hurricane in the United States of 2020.  That ties 2020 with the 1916 season for most landfalling systems in the contiguous United States.  By comparison, eight storms made landfall in the United States during the entire 2005 season. 

It’s also worth noting that 2005 was the only previous season that was so active it necessitated using the Greek alphabet to name tropical systems.  Consequently, Tropical Storm Beta was the first storm with a name from the Greek alphabet to ever make landfall in the United States.  NOAA’s forecast for the 2020 hurricane season cited the development of La Nina conditions as a primary factor in it being an active one.  Hurricane season runs through November 30.