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June 2015

Early Summer Heat Waves in June



Although the official definition of a heat wave is three or more consecutive days with highs of 90° or hotter, I've relaxed it a bit for this analysis and have included days in the upper 80s, as well as one or two cooler days if they fell between periods of hot weather.  With that established, here are eleven of the more notable hot spells that have occurred in the past 100 years.



2008 (June 7-10) - Although just four days long, the average high was 94.8°, the second hottest of June hot spells. 

2003 (June 24-27) - Besides four readings in the 90s this hot spell also had a low of 79° on June 26, the warmest low in June since 1984 (but it came sixteen days later than 1984's).  Interestingly, even with these four hot days, the month was 2.6 degrees cooler than average (and the coolest in 31 years).  Without these four days the month was four degrees below average. 

1994 (June 14-26) -  At 13 days this is the lengthiest warm spell in June (June 1953 had one of twelve days).  Six days were in the 90s.  The high on June 18 reached 98°; three days earlier, the high was 96°.  The month became the third warmest June on record. 

1984 (June 7-13) - The  hottest period in the summer of 1984 occurred during this seven-day stretch in the second week of June.  The average high/low during this week-long steam bath was 93°/75°, with six of the seven days having highs in the 90s (the rest of the summer had four 90-degree days).  The mean temperature of 83.8 was the second hottest for June hot spells, just 0.1 degree below a four-day heat wave in the middle of June 1956.  But it was the most above average, +14 degrees.  The low on the morning of June 10 was 79°, seventeen degrees above average (and one degree higher than the date's average high).




1966 (June 20 - July 15) - This hot spell began on June 20 and stretched thru mid-July, but even just the 11 days in June makes it one of the lengthiest for the month.  It's probably best remembered for the 101° high on June 27 (second earliest date for a triple-digit high).  The period in June and July were both seven degrees above average.  And earlier in June there was a six-day period that saw temperatures 10 degrees above average.  Overall, this became the second warmest June on record. 

1957 (June 12-19) - This eight-day long stretch of hot weather duplicated a mid-June heat wave from the previous year, but this one lasted twice as long.  These days were eleven degrees above average, with the last five days all in the 90s (peaking at 95° and 96° on 6/16 and 6/17, respectively). 

1956 (June 13-16) - The mean temperature during this four-day heat wave, 83.9° (13 degrees above average), is the highest of all the periods in this analysis.  On June 14 the high reached 99°. 

1952 (June 15-27) - This stands out because two hot periods, of five days and three days, book-ended three days with highs only in the 60s (averaging 63°).  It's also memorable for having the earliest date for a 100-degree high (June 26) - and the only low in June in the 80s (81°).  There was also a high of 99° on June 25.   

1943 (June 19-28) - Eight of the ten days were in the 90s, including highs of 99° on June 25 and 98° on June 27.  This would become the warmest June on record (a position it still holds).




1925 (June 1-7) - This week-long hot spell during the first week of the month had an average high of 95.0°, twenty-one degrees above average, making it the hottest average high of any of the June heat waves in this analysis.  This included back-to-back highs of 99° on June 4 and 5 (which followed a high of 98° on June 3).  June would be the warmest month of the summer of '25, and at the time it was the warmest June on record (it now ranks sixth). 

1921(June 21-29) - Although the amount wasn't excessive, this is the June hot spell with the most rain.  Six of the nine days had rain, which totaled 1.47" (and 0.78" fell on 6/30).  These nine days saw a four-day heat wave at the onset as well as two days with highs of 88° and two with highs of 89°.  Average high during this sultry period was 89°.





Near-Record Warmth of May 2015 Mirrored February's Near-Record Cold


After the harsh February we experienced (the third coldest on record) you might think New Yorkers would be well aware that May 2015 was unusually warm.  Yet most of my friends seemed surprised when I told them that it was the second warmest on record (after May 1991).  They seemed to think the temperatures we experienced were typical.  Yes, it was normal - for June.  May's average high of 78.4 (nearly eight degrees above average) was only one degree lower than what the average high in June is. 


Perhaps they took little notice because there was no excessive heat, i.e., no readings in the 90s.  In fact, among the eleven Mays that have had 11 or more days in the 80s, May 2015 was the only one with no 90-degree readings.  However, there were 18 days with highs of 80° or warmer, a new record, passing May 1991's seventeen.  (A typical May has six such days.)  Conversely, it had the fewest days with highs cooler than 70°, just three (the average is twelve).


May 2015 ended up being 0.2 degrees cooler than May 1991.  This was due to the fact that 1991 had five days in the 90s.  (The average high of the days that were in the 80s or warmer this May was 83.8° while the days in the 80s in May 1991 averaged 86.5°.)  However, this did become the May with the mildest average low, 0.1 degree warmer than May 1991.




Besides the warm temperatures May was also very dry - until the last day of the month.  Through May 30 just 0.40" of rain had fallen, and it appeared this was going to be the first May since 1964 to have less than an inch of rain.  Then strong thunderstorms moved in around 5PM, and 1.46" of flooded the City in just a few hours.   


(1991 & 2015)
  2015 1991
Average High 78.4 78.9
Average Low 58.6 58.5
Mean Temperature 68.5 68.7
Days of 80+ 18 17
Days of 90+ 0 5
Hottest Temperature 88 93
Lows of 70+ 3 4
Lows in the 40s 3 3
Highs Cooler Than 70 3 7