Ranking Hot New York Summers by Concentration of 90-Degree Days

 

Looking at the number of 90-degree days as the sole criterion for gauging how hot a summer has been is a fairly standard measure, but it can be misleading.  For instance, it doesn't take into account the fact that in some years 90-degree days are spread over considerably more weeks than other years.  That is the subject of this analysis.  For my purposes I'll be referring to the period between a year's first and last 90-degree day as the "window".  New York's typical 90-degree window (based on 1980-2020) is a few days shy of 13 weeks, starting in late May and continuing thru late August.  During this window, one in five days, on average, will see a high in the 90s or triple digits. 

 

Looking at records dating back to 1872, the most 90-degree days in a year has been 39 - and it happened twice - in 1991 and 1993.  However, while 1991's occurred over a lengthy span of 23 weeks, 1993's were more concentrated, occurring over five fewer weeks.  1991's hot days, in other words, were more "diluted".  While 1991 experienced 90-degree temperatures during 24% of its "window", 1993's corresponding figure was 31%. 

 

 

Yet, neither of these hot summers come close to 1999.  Although that year had ten fewer 90-degree days, they were concentrated in a sixty-day window.  That means that close to half of the days during its 90-degree window were in the 90s.  And 1988 wasn't far behind, with 33 90-degree days over 77 days (43% concentration).  Four other years with a considerable number of 90-degree days (24 or more) also had a higher concentration of 90-degree temperatures than either 1991 or 1993.  So, you be the judge over which summer was hotter.  

 

 

The chart below ranks years with more than two dozen 90-degree days based on their concentration of hot days that occurred between their first and last 90-degree day.  (Although the summer of 2015 doesn't qualify for inclusion on the chart because it had twenty 90-degree days, its concentration was 25%.)

 

I'd like to to thank fellow weather fanatic, Eugene DeMarco, for helping me by supplying and organizing some of the weather statistics that provide the background material for this post. 

 

 

 

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Comments

[Arthur L Morrone]

This extensive data clearly shows that atmospheric CO2 concentration has nothing to do with hotter weather. NYC has experienced many hotter summers prior to the year 2000. People are confusing natural variability with extreme climate change. If you go back in the climate record just 5,000 to 10,000 years ago the Sahara Desert was a tropical rain forest. Now thats real climate change and 10,000 years is a blink in the geological eye.

[Rob]

Although I’m not a climate scientist, I do think that what’s being belched into the air worldwide by all types of vehicles, airplanes, factories, as well as wood and coal burning stoves (especially in India and China) has had a warming effect on the climate, perhaps accelerating the arrival of the next period of climate warming, Additionally, for the past 10 years temperatures in NYC have risen more at night than during the day, which is attributed to greater cloud cover, caused by there being more moisture in the air. This keeping the temperature from rising as much as before during the day, while preventing the day’s heat from escaping at night, thus keeping the temperature from dropping as much as it used to at night.