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September 2020 Weather Recap: Cool & Dry Conditions Sandwiched Between Mild & Wet

September 2020

 

September 2020 was a touch milder than average (+0.8 degree), with close to an average amount of rain (3.94").  The month's story can be told by three eight-day periods: Sept. 3-9 was four degrees above average, Sept. 23-30 was six degrees above average, and the middle of the month (Sept. 15-22) was six degrees chillier than average, and rain-free.  Nearly all of the month's nearly four inches of rain was produced by three storm systems: 0.71" on 9/3, 1.20" on 9/10 and 1.61" on 9/29-30. 

 

The month's near average rainfall belied a 16-day streak with no measurable rain (Sept. 11-26).  This was the longest dry streak since the fall of 2017.  These dry conditions were largely due to a strong high pressure system that anchored itself over the Northeast for about a week.  It prevented moisture from hurricane Sally and tropical storm Beta from moving into the area and brought chilly air into the region, delivering the City's earliest lows in the 40s in seven years (49° on 9/21, 48° on 9/22).

 

Just seven days had highs of 80° or warmer, joining ten other Septembers since 1970 with this few.  The warmest reading was 85°, occurring on 9/3 and again on 9/4 (a typical September's hottest reading is around 90°).  The month's average high of 75.5° was the coolest since 2009.  And although the month's average temperature was a touch above average, it was the coolest September since 2013.

 

Chart - septembers by decades

 

Finally, although highs in the 80s/90s and lows in the 70s occasionally occur in October, if 2020's final reading of 80°+ remains at 9/10, it will be one of the earliest dates on record for this occurrence.  Meanwhile, the 58 lows of 70°+ is the third most after 1906 (61) and 2005 (60). 

Here are previous September recaps:

2019

2018

2017

2016

2015

2014

 


September 2019 - One of 10 Driest Septembers On Record

September

 

September 2019 was the first month since October 2013 to have less than an inch of rain and was the eighth driest September on record (0.95" was measured).  Thru 9/20 the month had average temperatures, then the last ten days were eight degrees warmer than average, resulting in the month being 2.4 degrees above average (24th warmest since 1869).  Although it was warmer than average, the month had just one low of 70º+, the fewest in September in ten years (there were none in 2009).  It was also the first September since 2011 not to have any highs of 90° or hotter. 

 

This September added to the record set last year when September 2018 was the fourth in a row with an average temperature of 70.0 degrees or warmer.  September 2019, however, was the "coolest" of the five.  However, a record that was tied last September, the sixth September in a row with a high in the 90s, wasn't broken this year as the hottest temperature this was 89°.  (It occurred on 9/23 - the same date as the month's only low in the 70s).

 

Chart - past five septembers

 

Two-thirds of September's paltry amount of rain fell in the first six days of the month, split mostly between Labor Day (when 0.30" fell mid-day, the most to fall on the holiday in sixteen years) and 9/6, when the most northernmost band of hurricane Dorian dropped 0.27" in less than an hour during mid-afternoon.

 

Chart - 10 Wettest Septembers

Finally, humidity of 15% or lower occurs very infrequently in New York, and when it has happened it's been confined to March and April (in the years since 2000) - until 9/19, when it dropped to 15% for a few hours that afternoon.  The last time the humidity was this low in September was on Sept. 11, 2001, when it bottomed out at 16%.

 

Here are recaps of the five previous Septembers:

2018

2017

2016

2015

2014

 

 Sept 15 - lower manhattan



 

 


September 2018 - A Month With Unusually Mild Nights

September 2018

 

September 2018 was 2.7 degrees warmer than average.  Like August, its average low was considerably more above average (+4.4 degrees) than its average high (+1.0).  This resulted in a vast difference in their historical rankings, with the average high ranking 60th warmest while the average low was ensconced among the ten warmest, at #4 (overall, the month was the 21st warmest).  The month's other significant story was its rainfall, which amounted to 6.19" - the most in September in seven years.  Furthermore, this was the sixth month this year with more than five inches of precipitation, joining ten other years with this many or more.  And if that wasn't impressive enough, 2018 became just the second year to have these six months concentrated in the first nine months of the year (1998 was the other year). 

Additional points of interest:  

  • The remnants of two hurricanes brought 1.38" of rain on 9/9-10 (Gordon) and 1.19" on 9/18 (Florence).  However, the month's biggest rainstorm was on 9/25 when 1.95" fell. Nearly half of that day's rain poured down in about an hour early in the afternoon.
  • The first full week of the month (week of 9/3) had four days in a row with highs that ranged from 89° to 93°.  The average high/low of 91/76 during these days was twelve degrees above average.  The first day of this hot spell fell on Labor Day, which had a high in the 90s for just the fourth time since 1980. 
  • This was the fourth September in a row with an average temperature warmer than 70.0 degrees, the longest such streak on record.  What's more, the month set a September record for the most days with lows of 67° or warmer (seventeen; the average number is six).  Despite this surfeit of warm nights, the number of days with highs of 80° or warmer was a bit below average (nine).
  • The month's average diurnal variation (the gap between the average high and low) was the smallest for September in more than 100 years (since 1908).  In 2018 it was 11 degrees, well below the average of 16 degrees (based on the past 100 years).
  • This was the record-tying seventh year in a row in which September experienced highs in the 90s, equaling in length the streak of 1940-1946.
  • Like September, August's average low also ranked fourth (its average high ranked 32nd).
  • Typically September is 2.5 degrees cooler than June, but this year it was one degree warmer.  This is the fifth time it's happened since 1980 (most recently in 2015).

 

 Chart - september warmest lows

Here are recaps of the four previous Septembers:

2017

2016

2015

2014

 


Recap of September 2017 Weather: The Great Rebound

ReboundAfter experiencing the coolest start to the month since 1975 (thru 9/12), a complete turnaround occurred, with temperatures nine degrees above average during a streak of sixteen unseasonably warm days (thru 9/28).  This included a record high of 91° on 9/25, the first 90-degree reading since 8/1, and the latest temperature in the 90s since 1970.  As a result of this rebound the month ended up being 2.5 degrees above average, the fourth year in a row in which September had warmer than average temperatures.  (The final two days of the month reverted back to the cool conditions experienced at the beginning of September, but by then such temperatures were close to average.)  Other highlights:

 

 

  • With just 2.00" of rain, September was the driest month since August of last year (when 1.97" was measured), and the sixth driest September since 1980.  Much of the rain fell in a 12-hour period on the night of 9/2 into the early morning hours of 9/3 (1.27").  No rain fell in the last 11 days of the month, tying an equally long streak in February as the longest dry spell of the year.  (This dry spell continued into the first week of October.)  The month's last rainfall, 0.22" on 9/19, was produced by Hurricane Jose, which New York was on the western edge of.
  • September's average temperature was 3.5 degrees cooler than August's, the closest September has been to August since 1961 (the average difference is 7.2 degrees). 
  • This was the sixth September in a row to have at least one high in the 90s, the longest such streak since one of seven years from 1940 to 1946 (which would be tied in Sept. 2018).
  • The last day of the month and 9/2 had the month's coolest reading, 54°.  However, while this reading was eleven degrees below average on 9/2, it was just one degree below average on 9/30.
  • Although it fell during the cool first part of September, Labor Day was sunny and pleasant with a seasonable high/low of 80/61.
  • The average high/low of 74/59 in the first twelve days of September was followed by a warm 82/69 from Sept. 13-28.
  • Embedded in the sixteen-day streak of unseasonably warm temperatures were five days in a row (Sept 23-27) with mean temperatures 10 degrees or more above average, the longest such streak in 20 months (October 2017 would have a streak that lasted seven days).  Temperatures were 14 degrees above average during these five days, with an average high/low of 87/69.
  • This was the third September in a row with an average temperature of 70.0 degrees or warmer, making this the longest such streak on record.

 

Sept 2017

 

Here are links to September summaries of the previous three years:

September 2016

September 2015

September 2014

 

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September 2016 Weather Review - Summer Hangs On

September songSeptember 2016 was characterized by seasonable temperatures at both the beginning and end of the month and unseasonably warm conditions during the days in between (Sept. 6-23); temperatures during this summery two-and-a-half week period were nearly seven degrees above average.  As a whole the month was 3.8 degrees warmer than average, tying Sept. 1983 and 1884 as the tenth warmest on record (this followed the third hottest August).  Three days had highs in the 90s and seven had mean temperatures that were ten degrees or more above average (one of which was the first day of autumn).  There were just five days with below average temperatures.  The most below average was 9/30, with a high of 59/56 (it was the high that was below average, by 11 degrees) - this was the first day in September with a high in the 50s in fifteen years. 

 

50 Deg Highs in Sept 

OTHER SEPTEMBER HIGHLIGHTS

  • The high on Labor Day was 84°, which was the same as Fourth of July and very close to Memorial Day's high (82°).  This was just the third time since 1970 that that three summer holidays had very similar highs.  But whereas Memorial Day's high was seven degrees above average and Labor Day's five above, 4th of July's was at the seasonal average.
  • On Sept 11 the heat index was 101°.
  • The three 90-degree days in September brought the year's total to 22, five above average and the most since 2010.  The 91-degree reading on 9/14 was the latest high in the 90s since 1995 (when it occurred on 9/15).
  • Although September's rainfall was below average, more fell than in August (2.79" vs. 1.97").  There were no storms that produced an inch or more of rain but three had a half-inch or more (on 9/14, 0.56" poured down in an hour during a late afternoon thunderstorm).  The rainiest day was 9/19 when 0.68" fell.  Since March, all but one month (July, with 7.02") has had below average rainfall, resulting in a deficit of nearly 10 inches in these seven months (20.91" vs. 30.78") .

 

September sun

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The Towering Clouds & Beautiful Sunsets During Summer 2016

Sheridan sq sunset

 

I've always had an appreciation for clouds and sunsets.  Five years ago I probably wouldn't have been able to write this post because I didn't have my smartphone with its camera.  Now I'm able to snap photos at a moments notice, enabling me to capture this summer's overabundance of photo-ready thunderheads and stunning sunsets.  And because I live in the West Village I probably notice them more since the low-rise buildings make the sky much more accessible than in Midtown Manhattan.  I hope you enjoy the photo revue that follows ... 

 

 

Sunset in my face
The photo display begins with one of me along the Westside Highway at dusk during Memorial Day weekend.

 

Rays of sun
Rays of the setting sun stream over Sheridan Square in Greenwich Village.

 

Sunset in mckees rocks
I took this photo during a June visit to Pittsburgh to see my mother. These clouds brought to mind those I'd often see over the Atlantic Ocean close to sundown on Fire Island.

 

July 1 2016
Taken on July 1, this photo shows a thundercloud from a storm that struck half an hour earlier. Although it was around 9PM the top of the cloud was catching the rays of sun that was below the horizon.

 

Sun thru slate gray
Early evening sun filtered through a slate gray sky over Sheridan Square.

 

Towering thunderclouds in glen rock
This isn't a cloud formation in New York but it deserves an honorable mention.  I snapped the photo of this breathtaking thunderhead during a weekend visit to south central Pennsylvania in the midst of a late July heat wave.

 

Moonshine
Taken from my kitchen looking east as the full moon was rising.

 

Sunset aug 3
This was the view on 7/28 looking east from the 44th floor of an apartment building on the  Upper West Side. The light pastel coloring was the result of a fire in a warehouse in Long Island City (Queens) an hour earlier.

 

Gathering clouds by grand central
Taken as I was walking to the subway after work on 42nd St. across from across from Grand Central Terminal.

 

Glorious clouds and sun
Looking west from Sheridan Square at around 6PM in mid-August. Seeing it I felt I was in the presence of the Divine.

 

Cloud tower
Early evening on a hot day in mid-August.  These mountainous clouds brought a quick downpour to upper Manhattan, but not to Greenwich Village.

 

Towering
Similar view and thunderclouds as the previous photo but on a different day one month later.

 

10 charles street
The same cloud formation as it moved behind the apartment building at 10 Charles St.

 

Puffy and wispy
Wispy and puffy clouds over the West Village.

 

Sunset christopher pier
Sunset on the Saturday of Labor Day weekend, taken on Christopher St. pier, which looks out across the Hudson River.

 

Pastel sundown
This is how the sun's rays from the above sunset reflected on the bank of towering clouds in the east.  Reminds me of rainbow sherbet.

 

Up from subway
I snapped this photo shortly after I came out of the Christopher St. subway station in the early evening. This view is looking east.

 

Orange red sunset
Taken the evening of Sept. 11 as I left the gym on Seventh Ave. South.

 

Sept14 sunset
Taken on Sept. 14 close to the West Side Highway in Chelsea, shortly after a late afternoon thunderstorm. A few hours earlier the temperature was in the low 90s, the last 90-degree day of the year.

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Lga sunset
6PM on Sept. 15, awaiting take-off at LaGuardia Airport.

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Golden sunset
Finally, a golden sunset on Sept. 17 during a visit to my childhood neighborhood in McKees Rocks, PA.

 

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September 2015 Weather Recap: New York's Warmest on Record

Trophy.winner

 

After experiencing near record-warmth in May (second warmest) and August (third warmest), 2015 can now lay claim to the warmest September on record, easily topping 1961's previous record by 0.9 degrees.  Like much of the summer, September's average temperature was greatly influenced by the lack of any incursions of chilly air masses.  The coolest reading was 56°, which matched Sept. 1921 for the mildest minimum reading for the month.  (September's coolest reading is typically around 49.)  And only five days had lows in the 50s, which was well below the average of 13.  Finally, the month joined Sept. 1968 and 1921 as the only Septembers to have no high temperatures cooler than 70°.  A typical September sees five or six such days.  Other interesting facts:

 

  • Nine days had mean temperatures (average of the high/low) that were 10 degrees or more above average, but that was no match for the 14 such days in Sept. 1961.  (1961's average high was just 0.1 degree lower than 2015, but 2015's average low was 1.7 degrees milder.)
  • This September matched that of 2005 by having just one day with a below average mean temperature.  However, in 2015 that day was just one degree below average while 2005's was four degrees below the norm.  (And Aug. 2015 had only a handful of days that were below average, and they were all also just one degree below average.)
  • This was the first time since 1998 that September was warmer than June, which was close to average (74.4 vs 71.2).
  • Despite this year's record warmth, Sept. 1961 had more 90-degree days (8 vs. 6) while Sept. 2005 had more 80-degree days (23 vs. 19).
  • The hottest high temperature of the year occurred on 9/8 when the mercury reached a record 97 degrees.  (However, the year's highest mean temperature occurred on 7/20, with a high of 94/82).

 

Highline

 

  • The month saw the end of the longest streak of 80-degree days on record, 62 days.  Then shortly thereafter another warm temperature record was established - most total days  of 80-degree+ in a year (which grew to 114 days by the end of the month).  In both instances the previous record holder was 1944.  (Despite this record number of 80-degree days, 2015 ranks 12th for most lows of 70 or warmer.)
  • The month was on the dry side and featured a 15-day stretch with no rain (the second longest streak of the year).  In total 3.28" of rain fell, with most of it falling on two days - a record 1.51" on 9/14 and 1.27" on 9/30.  And although the month had below average rainfall (one inch below average), it had considerably more rain than any of the next eight warmest Septembers, which averaged just 1.58".

 

10 WARMEST SEPTEMBERS 
(Since 1900)
           
  Mean Average Max Min
 Year Temp High Low Temp Temp
2015 74.4 82.6 66.3 97 56
1961 73.5 82.5 64.6 95 49
2005 73.3 81.6 65.0 92 50
1959 72.3 80.9 63.6 93 46
1931 72.3 81.3 63.3 99 49
1921 72.1 80.7 63.5 96 56
1930 72.0 79.8 64.1 88 52
1983 71.8 80.5 63.0 99 49
1971 71.5 77.3 65.8 91 49
2010 71.1 78.7 63.4 96 54
           
Source: NOAA Local Climatological Data

 

 

 

 

 

 

 

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Summer of 2015 Highlighted by Record Streak of Days Above 80 Degrees

80Plus

 

The Arctic air that was entrenched over the Northeast during the harsh winter of 2015 became a distant memory later that summer when New York experienced 62 days in a row with high temperatures of 80° or warmer (July 10-Sept. 9).  This was a record streak, besting the previous record from 1944 by three days.  (On the day the streak ended the high was 79°.)  Of course, summertime temperatures in the 80s or warmer aren't unusual; what was unusual is that for nine weeks there were no incursions of Canadian air or back-door cold fronts from New England.  (These are responsible, on average, for twelve days with highs in the 70s or cooler in July and August.)  The average high during these weeks was 87.5°, five degrees above average.  Below are some other tidbits of interest:

 

  • This year's streak joined ten others that were five weeks or longer.  Among them, four have occurred since 2005.
  • 2015's s streak included 19 days in the 90s, but 1944's and 1966's (second and fifth longest, respectively) had even more, 30 and 23.  And among the ten longest streaks, the streak in 1966 was the hottest, with an average high temperature of 91°.
  • 2015's streak was instrumental in making the August 2015 the third hottest on record and July/August the fifth hottest.
  • Finally, this year's streak of warm days matched a streak of cold weather during the winter when another record was set - 61 days in a row with high temperatures that never went above 45°. 

 

LONGEST STREAKS OF 80-DEGREE+ HIGHS
           
# of      Average Days Days
Days Year Dates High 90s 80-81
62 2015 July 10 - Sept 9 87.5 19 4
59 1944 June 26 - Aug 23 89.7 30 5
41 2011 July 4 - Aug 13 88.8 17 1
41 1943 July 8 - Aug 17 87.4 14 1
40 1966 June 20 - July 29 91.0 23 2
37 1917 July 16 - Aug 21 86.1 5 3
36 1999 July 15 - Aug 19 89.5 17 2
35 2008 July 7 - Aug 10 86.4 7 7
35 2005 Aug 20 - Sept 23 84.2 3 6
35 1998 July 9 - Aug 12 85.5 3 3
35 1953 June 18 - July 22 88.6 15 2
           

 80degdays

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90-Degree Days in September

Hotweather.1940s

 

September is more likely than May to see 90-degree temperatures.  While May experiences a 90-degree day once every three years, September sees one about every two years.  The most such days in occurred in 1961, when there were eight, followed by seven in 1895, 1970 and 1983.  The most consecutive years to have a 90-degree reading in September is eleven, from 1936 to 1946.  (More recently, there was a seven-year streak between 2012-2018.)  The most consecutive years without one is six, from 1885 to 1890.  Finally, three days in September have never had a reading in the 90s: 9/28, 9/29 and 9/30 (9/24 was on this list until 2017). 

 

Only four of New York's ten warmest Septembers are among those with the most days in the 90s: 2015 (warmest September on record/six 90-degree days); 1961 (second warmest September/eight 90-degree days); 1931 (sixth warmest/five 90-degree days); and 1983 (tenth warmest/seven 90-degree days).  And one of the ten years with the most 90-degree days, 1988 (32 days), reported no 90-degree days in September.

 

Lastgaspofsummer

 

Finally, there have been five years with 90-degree readings in October - four were concentrated between 1938-1941, and the last time was in 2019.  Two of those years were back-to-back (1938 and 1939), and in both years there were no 90-degree days in September.  October 1941 had two 90-degree days, including the hottest October reading on record - 94° on 10/6.  In addition, there have been nine  years in which there were 90-degree days in the last ten days of September, most recently in 1980.

 

Most 90 Degree Days in September

 

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The 'Last Gasp' of Summer - Noteworthy Late Summer Warm Spells

Cool.dog

 

Late season heat waves can be great if your vacation happens to coincide with one of them, or if it occurs over the Labor Day weekend.  However, they can also be unwelcome, especially in years when a hot summer doesn't want to let go of its grip (as was the case in 1980, 1983, 1993 and 2010).  Since 1940 there have been more than two dozen of these last gasps of summer (of at least five days).  Some are distinguished by temperature, others by number of days.  For this analysis I discuss seventeen I found to be of greatest interest. (By "late season" I'm referring to any unseasonably warm spell that occurred between Aug. 20 thru about Sept. 20.) 

 

1947 (Aug. 22-26 and Sept. 7-15)

1947 is the only summer in this analysis with two late warm spells.  The first had an average high of 91°, which was nine degrees above average; the second's average high of 86° was ten degrees above average.  

1948 (Aug. 25-30)

This six-day sizzler merits attention because three of the days had highs in the triple digits and two others had highs of 95°.  With an average high/low of 97/76 this is the hottest of the late summer heat waves.

1953 (Aug. 24 - Sept. 5)

This one is the stand-out of all the late season hot spells - all twelve days were in the 90s, including six in a row with highs of 97° or hotter (two of which were in the triple digits).  This is also the longest heat wave in NYC history.

1959 (Aug. 25 - Sept. 9)

This sixteen-day stretch followed an eleven-day hot spell between Aug. 12-22 that ended when two days had unseasonably cool highs in the low 70s.  Then the heat returned beginning 8/25 and continued for sixteen days.  And there would be an early autumn warm streak of nineteen days from Sept. 22 thru Oct. 9.

1961 (Aug. 25 - Sept. 14) & 1964 (Aug. 22 - Sept. 11)

These two are grouped together because they were very similar.  Both lasted for 21 days, the lengthiest of any of the late summer warm spells.  And both had very similar dates.  1961's was a bit hotter than 1964's, with an average high/low of 89/71 versus 87/65; 1961 had nine 90-degree days while 1964 had seven.  However, unlike many of the periods of unseasonably warm weather, there were no highs hotter than 95° in either year.  1964's sultry period was notable because the first three weeks of August had been very cool, five degrees below average, with just one day reporting an above average mean temperature.  

1973 (Aug. 26 - Sept. 5)

Very similar to the late summer heat wave of 1953, this one featured eight days in a row with highs in the 90s, including highs of 98° on 8/28 and again on 8/30.  For the entire eleven-day stretch the average high was 93°.

1979 (Aug. 25 - Sept. 7)

Although three days were in the 90s, what was more striking was the twelve days in a row with lows in the 70s.  The average low during these days was 74°, nine degrees above average. This warm spell was also distinguished by having the smallest difference between the average high and low, twelve degrees.  The only late summer warm spell with a warmer average low would come six years later (but it lasted only five days).  This warm spell featured a cameo by the remnants of hurricane David, which dropped 1.29" of rain on the morning of 9/7.

1980 (Aug. 23 - Sept. 7)

Half of the sixteen days were in the 90s (five of which were 95+) and three other days reached 89°.  The average high for this stretch f days was 90°, ten degrees above average.  (Fifteen days after this hot spell ended the high reached 94° degrees on 9/22.)

1983 (Sept. 3-12)

The highlight was a high of 99° on 9/11, the hottest reading of a hot summer.  And the mercury hit 97° the day before.  Overall, these ten days had an average high of 91°, which was fourteen degrees above average.

2005 (Sept. 12-23)

This was one of the latest of the late incursions of summertime heat; it was also part of 35 days in a row with highs in the 80s that began Aug. 20.  This five-week period was also very dry, with just 0.33" of rain measured in Central Park.

2010 (Aug. 29 - Sept. 2)

The hottest summer on record extended into the first few days of September during this five-day streak of temperatures in the 90s.  And Sept. 3 would probably have reached into the 90s as well if not for cloud cover brought by hurricane Earl (the AM low was a sticky 75°).  Five days after this hot stretch ended saw two days with highs of 89° and 90°.

2014 (Aug. 29 - Sept. 5)

In 2014 New York didn't experience an extended period of hot weather until late in the summer.  Seven of the eight days saw highs of 88° or hotter, with four of them in the low 90s.

2015 (Aug. 30 - Sept 9)

This eleven-day period began with a five-day heat wave and ended with a three-day heat wave, which included the hottest reading of the year, 97°, on Sept. 8. 

2016 (Aug 26-31)

For the third year in a row late summer featured unseasonably warm weather.   Earlier this summer there were two five-day heat waves, and while this six-day period didn't meet the definition of a "heat wave" (i.e., every day has a high of 90+), these days were eight degrees above average.  

 

Summer

 

2018 (Aug. 27 - Sept. 6)

This eleven-day stretch was comprised of two four-day periods of hot weather at the beginning and end, with three close to average days in between.  Each four-day period had three days in the 90s and three days with lows of 75°+.  The average high/low of the entire eleven days was 88/75°, eight degrees above average.  The average low is the warmest of any late summer hot spell of ten days or longer.

 

 Chart - Hottest Late Summer

Chart - Last Gasp of Summer

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