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August 2019

Cooling Thunderstorms Prevented July 2019 From Ranking Among 10 Hottest Julys

Lightning strike nyc

 

As July 2019 came to a close it appeared the month was about to join three other Julys from the 2010s ranked among New York's ten hottest Julys.  As late as 3:00 PM on 7/31 the day's high/low was 87°/76°, and if that low temperature held, the month would have tied July 1966 as ninth hottest (both with average temperatures of 79.66°).  But then mid-afternoon thunderstorms erupted between 3-4:30 and the temperature tumbled to 70° - making it the day's new low.  This brought July 2019's average temperature down to 79.56°, pushing it to eleventh place, 0.05 degree cooler than July 1949 (79.56° vs 79.61°).  However, as a consolation prize, July 2019's average low was warm enough for it to rank fifth in this category. 

Other observations:

  • Besides the thunderstorms of 7/31, thunderstorms on 7/17 and 7/22 also resulted in lows that occurred in the evening.  Much of the month's rain fell from these two rainstorms, with 2.33" falling on 7/17-18 and 2.19" on 7/22-23.  So far this year these are 2019's two biggest 24-hour rainfalls.  And with 5.77" measured July 2019 became the second rainiest of the fifteen hottest Julys.  This was after just 0.08" of rain fell in the first ten days of the month.  (Last July, which had nearly seven-and-a-half inches of rain, also started out dry, with just 0.24" measured in the first eleven days of the month.)

 

Chart - rainfall 15 hottest julys

  • There were ten days in July with highs of 90°+ (average is eight), making it the sixth July of the decade to have this many, the most of any decade.

 

Charts - 90s in july by decades

 

  • This July joined 36 others that have had ten or more days with highs of 90°+.  However, July 2019's ten torrid days had the "coolest" average temperature, tied with July 1887 (91.7°).  July's hottest temperature, 95° on 7/20 and 7/21, was one of the coolest readings for hottest temperature among the Julys with ten or more 90°+ days; those other months' hottest readings averaged 99.4° (half of them had hottest readings in the triple digits).  But the average low on July 2019's hot days, 74.9°, was warmer than 24 of the 36 other Julys. 
  • July 1's low of 65° was the "coolest" reading of the month.  Only July 2008 has had a warmer "coolest" reading (66° on three dates).  The month had two days with lows in the 80s, which were the same two days that had highs of 95°.  It joined ten other Julys with two or more lows in the 80s.  Lastly, this was the unprecedented tenth year in a row in which July had no readings in the 50s.
  • What was notable about July 2019 was its consistent warmth but absence of extreme heat (excluding heat indexes).  26 days had highs of 85° or warmer, one shy of the July record, which has happened in three years: 1944, 1966 and 1993 (the average number of such days is 17).  Additionally, 24 days had lows of 70° or warmer, the second most on record; only July 2010 had more, with 25 (the July average is 15).
  • I refer to the week of 7/16 as as New York's "Hell Week" because, historically, it is the week most likely to have readings of 90° or hotter.  And this year six of July's ten 90-degree highs were concentrated during this week.  The one day not in the 90s, 7/18, was stuck in the 70s all day (high/low of 79°/71°) due to overcast skies and northeasterly winds.  Ironically, 7/18 has been the date most likely to have a high in the 90s/100s.

 

Cartoon devil

  • July was the third month in a row with more than five inches of rain, joining three other years which had five or more inches in May, June and July (1984, 1989 and 2009).  Although the 18.05" that was measured was nearly five inches above average it was significantly less than what fell in the other three years.

 

Chart - rainy may june july

  • Finally, for the fifth year in a row 4th of July had a warmer high than the previous year.  And with a high of 90°, this year's was the hottest 7/4 since 2012.

 

Here are recaps for the five previous Julys:

July 2018

July 2017

July 2016

July 2015

July 2014