Weather Quiz

Hurricane Harvey, August 2017  (Source: NOAA)

How many Category 4 hurricanes (excluding Laura) have made landfall in the United States since the Saffir-Simpson Hurricane Wind Scale was adjusted in 2012?  Prior to this change, a Category 4 hurricane had sustained winds between 135 – 156 mph, while a Category 4 storm now is defined as one with sustained winds between 130 – 156 mph.

A.  0

B.  2

 

C.  3

D.  5

August is Heating Up

High temperatures in the Nation’s Capital today will flirt with the 90° mark.  Several more days of 90° heat are on tap this week and Washingtonians are poised for one more heat wave before the end of August.  A “heat wave” is defined as a minimum of three consecutive days of 90° heat. 

As DC residents know, July 2020 was DC’s third warmest on record with 28 days of 90° heat.  But this month has been a different story.  Although it was 0.8° warmer than average through August 22, it has also been cooler than recent Augusts.  Four of the last five August’s have been warmer than average in the Nation’s Capital, with 2017 being the exception. 

So far this month there have been only four days of 90° heat, well below the total of 16 such days last year.  With several more days in the 90s during the upcoming week, the Nation’s Capital should finish between 2013’s total of six August 90° days and 2017’s nine such days.

Dating back to the early 1990s, the Nation’s Capital averages approximately 11 days of 90° August heat.  Of those 11 days, roughly three days feature high temperatures between 95° and 99°.  Washingtonians have seen triple-digit heat roughly every three to four years during the month of August.  The last time 100° heat occurred was in August 2016. 

While August is DC’s second warmest month of the year behind July, partially due to the gradually decreasing amounts of daylight, August can be warmer than July on occasion.  In fact, from 2000 – 2009, the month of August was warmer than July seven times in Washington, D.C.  However, since 2010, August has been warmer than July only once (2018).  The summer of 2016 was a very hot one in the Nation’s Capital, with July and August both finishing with the same monthly average temperature of 82.7° (combining daily high and low temperatures). 

There have been several notable late August heat waves in the Nation’s Capital in three of the last four years.  Some might wonder if this month’s above average rainfall has contributed to the lower number of 90° days.  While cloudy and/or rainy days can reduce high temperatures, it is possible to have both a very warm and wet month. 

Such was the case in August 2018, which finished 2.9° warmer than average with monthly rainfall more than 2” above average.  This month has been even wetter with over 6” of rain (more than double DC’s August rainfall average of 2.93”).  It has also had more cooler than average days (six) compared to all of August 2018 (four).  The moral of the story is that while August 2020 should finish close to 1° of average while being significantly wetter than average, it won’t be one of DC’s warmest or wettest August’s.

Feeling Like Fall ?

Following DC’s third warmest July and a warm start to August, there has been a discernable change in the weather over the last few days.  By the third week of August, average temperatures have fallen from their peak in mid-July.  DC’s hottest average daily high/low temperatures are 89°/71° for much of July, but are down to 86°/70° today.

The last few days have felt more like September than mid-August.  That’s because three of the last four days have been cooler than average.  You have to go back to mid-June to find a stretch of three or more consecutive days of cooler than average weather.  In fact, from July 1 – August 15 the Nation’s Capital had a total of only two cooler than average days. 

It has also been a wet August so far.  This morning’s rain makes today DC’s twelfth day with measurable rainfall since August 1.  While 6.22” of rain has occurred as of yesterday, DC would need at least 8.92” for August 2020 to rank among the 10 wettest on record.

Temperatures for this August in the Nation’s Capital are 1.2° warmer than average through August 18.  That’s cooler than it was for the same period last year.  DC had 11 days in the 90s between August 1 – August 18, 2019, while there have been only four such days so far this month.  While high temperatures haven’t been as extreme so far this August as compared to last year, overnight low temperatures have largely been warmer than average.  That’s an important factor to consider as above average daily low temperatures go a long way toward boosting average monthly temperatures.

Washingtonians recently set a record for longest consecutive stretch of days that temperatures remained at or above 70° from June 27 – August 15.  June 2020 was 1.8° warmer than average and last month was 4.1° warmer than average in the Nation’s Capital.  Nevertheless, there haven’t been any record highs or days with triple-digit heat. 

By the second-half of August the gradual shift toward fall is underway.  The sun sets at 7:56 PM today, compared to 8:37 PM on June 21.  Although mid-to-late August gradually sees decreasing average temperatures and a slow reduction in the amount of sunlight, it can still get quite hot this time of the year.  Such was the case during recent heat waves in the Nation’s Capital that spanned from August 27 – August 31, 2018 and August 17 – August 22, 2019.  In fact, DC’s high and low temperatures one year ago today were 98°/78°.  That tied not only DC’s record high for August 19, but also tied the daily record high-low temperature.

While no record-challenging heat is expected during the next 7 – 10 days in the DC Metro Area, NOAA’s Climate Prediction Center expects warmer than average temperatures for that time period.  Average high temperatures in the Nation’s Capital fall to 84° by August 31.