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June 2016 - The Dry Trend Continues

Hot, Wet New York Summers

Kids.in.rain

 

During the summer months clouds, thunderstorms or winds coming off the ocean often prevent temperatures from rising into the 90s.  However, there are occasional stifling days when high temperatures and thunderstorms co-exist, creating tropical conditions that wouldn't be out of place in Bangkok or Manila.  On average New York experiences about four of these days every year; most occur in July and August.  These downpours are usually of short duration (15 minutes up to a few hours).  This post takes a look at some of these summertime days that featured a combination of wicked heat as well as heavy rainfall. 

 

In the summer of 2019 the most tropical conditions were experienced on July 17.  On that day a severe thunderstorm between 8-9 PM dumped more rain (1.14") than what fell in the previous three weeks.  Earlier in the day sauna-like conditions prevailed as the dew point reached the mid-70s, the temperature rose to 93° and the heat index reached 105°.  It also appeared today would be one of those rare summer days with a low of 80°+, but when tonight's storm moved in the temperature dropped to 73°.  Rain continued after the initial storm, adding an additional 0.68", making this the wettest day of the year.  This moisture was from the remnants of what was hurricane Barry, which had flooded Louisiana earlier in the week. 

 

Three days have had highs of 100° or hotter and thunderstorms:

  • July 18, 2012 - High/Low of 100°/73°. 1.76" of rain fell from  severe thunderstorms that moved through between 2:30 and 5:00; most of the rain fell in the two hours between 2:40 and 4:40.  By 4:00 the temperature had fallen to 73°.  Before the storms moved in the heat index was close to 110° and during the early part of the thunderstorms the dew point was in the mid-70s.
  • July 21, 1991 - High/Low of 102°/74°.  0.46" of rain fell during a thunderstorm between 6-7 PM.  The heat index was between 105° and 110°.
  • July 14, 1954 - High/Low of 100°/69°.  0.37" of rain fell during thunderstorms between 10:30 PM -12:30 AM.  This was also the rainiest day of a dry July.

 

The following six days had hot temperatures and more than two inches of rain (ranked in descending chronological order):

  • Aug. 14, 2005 - High/Low of 96°/72°.  After the high temperature was reached around 2:30 PM three thunderstorms between 3 PM and 1 AM dumped 3.10" of rain.  The storm between 7-8 PM produced 1.70" (with nearly an inch falling in a 20-minute period) while the third storm dumped 0.83" between 10-11 PM.  Dew points were in the low to mid-70s and the heat index rose to 104° in the early afternoon.
  • Aug. 8, 2007 - This hot, wet day was different from the others in that torrential rain fell at dawn.  2.50" poured down between 5-7:00 AM, flooding (and shutting down large portions of the subway system).  And a tornado touched down in Brooklyn.  After a low of 73° the temperature rose to 90° in the afternoon.

 

Torrential rainstorm august 8 2007

 

  • July 21 , 1983 - High/Low of 95°/69°.  The 2.26" of rain that fell in the evening became known as the 'Diana Ross Thunderstorm' because it forced Ross to stop her free concert in Central Park when a severe storm bore down shortly after her performance began.  The rain fell heavily for three hours, from 6:30 until 9:30.
  • Aug. 26 1941 - On a day that had a high/low of 93°/68°, 2.30" of rain fell, most of it between 6:15 and 8 PM.  The day before 1.83" of rain in the early afternoon, but the high was only 75°.
  • July 1, 1933 - After a high of 94°, a heat index in the low 100s and dew points in the low 70s, 2.16" of rain poured down between 8:25 (when the temperature was 88°) and 10:45 PM.
  • June 27, 1932 - High/Low of 90°/72°.  Much of the day's 2.11" of rain fell between 8:00 and 10 PM, but there was also a quick downpour between 5:00 and 6 PM.  During the first half of the afternoon the dew point was in the mid-70s.  

 

And here are other days with highs mostly in the mid-to-upper 90s along with significant rainfall:

  • July 22, 2020 - High/Low of 92°/72° and 1.42" of rain, most of which fell between 6:30 and 7:30 PM during a severe thunderstorm.  The day's low had been 77° but fell into the low 70s during the storm.
  • July 25, 2016 - High/Low of 93°/73° and an inch of rain, which fell from 2:45 until 5:45 PM. During the thunderstorms the dew point rose to 77°
  • July 30, 2015 - A sultry high/low of 87°/76° was accompanied by a series of downpours and thunderstorms that produced 1.95" of rain between 1:00 and 5:00 PM.  During a 20-minute period between 1:24 and 1:44 an inch of rain poured down.  Afternoon dew points were in the oppressive mid-70s and the heat index reached the mid-90s before the rain moved in.J
  • July 7, 2012 - High/Low of 97°/72° and 0.50" of rain.  The rain fell during a late thunderstorm between 10 PM and midnight.
  • July 18, 2006 - High/Low of 95°/71° and 0.69" of rain.  Most of the rain was measured between 10-11 PM.
  • Aug. 2, 2002 - High/Low of 97°/70° and 0.70" of rain.  0.42" poured down in a 15-minute period between 8:15 and 8:30 PM.
  • July 8, 1994 - High/Low of 94°/73° and 0.82" inches of rain.  Much of the rain (0.70") fell from a thunderstorm between 3-4 PM.
  • Aug. 28, 1993 - High/Low of 95°/71° and 0.53" of rain.  All of the rain fell in an hour between 5-6 PM.
  • July 23, 1991 - High/Low of 99°/72° and 0.53" of rain.  A thunderstorm between 5:30 and 7 PM brought all of the rain.
  • July 17, 1988 - High/Low of 94°/71° and 1.21" of rain.  A strong thunderstorm dumped an inch of rain in an hour between 6:30 and 7:30 PM.  Earlier in the day there had also been showers in the wee hours of the morning.
  • July 1, 1971 - High/Low of 94°/73° and 1.56" of rain.  Thunderstorms moved in after 3 PM, with much of the rain falling from two storms between 3-4:00 (0.42") and 6-7:00 (0.65"). 
  • July 18, 1969 - High/Low of 94°/77° and 0.88" of rain.  All of the rain poured down in the hour between 4-5 PM.
  • Aug. 7, 1955 - High/Low of 93°/73° and 0.97" of rain.  The rain fell from a mid-afternoon thunderstorm between 3-4 PM and a nighttime thunderstorm between 9:30-midnight.
  • July 28, 1949 - High/Low of 97°/77° and 1.10" of rain.  (No hourly information is available for this month.)
  • Aug 16, 1944 - High/Low of 96°/73° and 0.88" of rain.  The rain fell between 5:30-8:40 PM.  This was the seventh day in a row with a high of 95° or hotter (and tomorrow would be the eighth).
  • July 11, 1940 - High/Low of 92°/67° and 1.94" of rain. (No hourly information is available for this month.)
  • July 7, 1934 - High/Low of 97°/74° and 0.83" of rain.  Rain fell during two thunderstorms between 8-9 PM and midnight-1 AM.  (The National Weather Service doesn't recognize Daylight Time and uses Standard Time year-round for its official records.)  Before the storms moved in the humidity was around 45% range but then jumped above 90% once the clouds opened up.
  • July 28, 1931 - High/Low of 97°/78° and 0.26" of rain.  The heat index was around 100°, and just before a mid-afternoon thunderstorm moved in it was in the low 100s as the humidity rose from 40% to 80%.  The rain fell in a short period of time, between 4:05 and 4:40 PM.
  • July 13, 1916 - High/Low of 94°/70° and 0.97" of rain.  Two thunderstorms produced the rain, between 4-5 PM and 6-8 PM.  Shortly before the storms moved in the dew point was an incredibly uncomfortable 80° and heat index at 3 PM was a wicked 112°.

 

For an entire summer, the hottest and wettest summer is that of 1991.  It was the 12th hottest and had 15.86" of rain (average amount is 12.50").  Second is the summer of 1983 which was fifth hottest and had 13.48" of rain.  Other warm and wet summers include 2011, 2006 and 1984.

 Heat and Rain

 

Rain forest

 

 

 

 

 

 

 

 

 

 

 

 

 

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Ken K. in NJ

Interesting study, thanks Rob. I do remember 8/7/07. It had rained in NJ and had already stopped. I was just leaving for work at 6AM and looked to the east and Brooklyn. The sky was as ominous as I have ever seen it. Absolutely a deep purple.

Your study raises a couple of questions for me.

I noticed that your table of "Heat & Rain Days" shows each day having a low in the 70's, so obviously the rain had somewhat of a cooling effect on each occasion. Was there ever a day with a low higher than 80 with any measurable precipitation?

And, forgive me if you've already done this, but on the topic of colling thunderstorms, do you have any data on the biggest one hour temperature drops?

Sorry if I'm making extra work, but I do find it interesting and have to ask.

Thanks again.

--Ken

Rob

Hi Ken,
There were a few days with lows in the 77-79 range that had thunderstorms, but none of the days with lows in the 80s had rain. Regarding the biggest temperature drops in an hour, monthly recaps after the early 1940s don't report hourly temperatures, but I believe I cited a 15 or 20-degree drop pre-1940 that I'll look for. Finally, I was out at Fire Island the morning of 8/7/07 and I remember hearing the rain approaching because of the sound the heavy rain made on the leaves of the trees in the distance.

Ken K. in NJ

Thanks Rob. I figured you had probably already looked into the biggest 1 hour temperature drops. If you come across the data again please re-post it. Thanks again.

PS: I seem to recall that one or two of the daily NYC newspapers used to publish hourly temperature data in the 60's and 70's, but maybe those were "unoffcial" readings.

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