Quantcast

Heat Feed

January Isn't Always the Coldest, July Isn't Always the Hottest

February

 

A reader recently asked if there have ever been any winters in which February was colder than January.  While it's not the norm, it happens occasionally.  Actually, more often than occasionally - 57 times, or nearly 40% of all years since 1869 (and it happened last winter).  In fact, New York's all time coldest month occurred in February 1934.  Perhaps of greater interest is the fact that there have been 17 winters in which December was the coldest month, the most recent being December 2005.  But the biggest anomaly of all occurred in the winter of 1960, when March was the coldest month!

For the most part, when February and August were colder/warmer than January or July it was when January was milder and July cooler than average.  However, there were six winters when both months were colder than normal (the most recent being in 1978).  And there have been four summers in which both months had above average temperatures (most recently in 2005).

 

August

 

 

 

 


July 2013's Overlooked Weather Story: Record Warmth at Night

Nycskyline_sunset

 

In weather discussions, low temperatures are like Cinderella - largely an afterthought.  Case in point, it was reported that July 2013 was New York's eighth warmest on record(now ranked ninth), but what was ignored was the fact that July's average low temperature of 73.4° was the warmest of any July in 100 years (and second warmest of all time, behind July 1908).  It beat the previous Julys with warmest lows, July 1999 and 2010, by a wide margin - 0.8 degrees.  It was only because of these warm nights that July 2013 ranked as high as it did, since July's average high of 86.3° was just the twenty-fifth warmest. 

 

What also stood out was July's small diurnal temperature variation of 12.9 degrees (i.e., the difference between the month's average high/low of 86.3/73.4).  In the past 100 years only July 2004's variation was smaller, and just by 0.1 degree (1996 had the same variation as this July).  Meanwhile, other Julys with warmer high temperatures than this year's had diurnal variations averaging 18.1 degrees.

 

A final observation - Although July 1966 is in the record books for having the highest average high temperature of any month, 90.3°, its average mean temperature of 79.7° is 0.1 degree below July 2013 because its average low was 4.3 degrees cooler than 2013's (69.1 vs. 73.4).  That July had a diurnal variation of 21.2 degrees.

 

Chart - 10 warmest julys ranked by low


 

 

 


Very Warm Low Temperatures Made July 2013 Heat Wave New York's Hottest on Record

Veryhot

 

In a recent post about New York's major heat waves, a key finding was that the nine-day heat wave of July 1977 had the distinction of being the hottest heat wave of seven days or longer.  This was based on the average high temperature.  However, when low temperatures are added to the equation a different story emerged. 

 

It turns out that New York's seven-day heat wave of July 14-20, 2013 had the warmest average low of any lengthy heat wave - 79.0°.  And although the average high during these days, 94.6°, put it in the middle of the pack, when it was averaged with the low temperature, the resulting mean temperature of 86.8° (the average of the high and low) made it the hottest of all the major heat waves.  It bested a heat wave in August 1988 by 0.1 degree.  And 1977?  It fell to third.

 

Heatwave5

 

12 HOTTEST HEAT WAVES RANKED BY MEAN TEMPERATURE  
(Heat Waves of 7 Days or More)  
           
    Average Average    
Year Dates (# of Days) High Low Mean  
2013 July 14-20 (7) 94.6 79.0 86.8  
1988 Aug 9-15 (7) 95.3 78.0 86.7  
1977 July 13-21 (9) 97.1 75.6 86.4  
1955 Aug 1-7 (7) 96.1 75.3 85.7  
1944 Aug 10-17 (8) 96.6 74.0 85.3  
1973 Aug 28 - Sept 4 (8) 95.4 75.0 85.2  
1993 July 7-16 (10) 95.7 74.5 85.1  
1983 July 12-18 (7) 95.0 74.9 85.0  
2002 July 29 - Aug 5 (8) 94.0 75.5 84.8  
2002 Aug 11-19 (9) 94.2 75.2 84.7  
1953 Aug 24 - Sept 4 (12)* 95.4 73.9 84.7  
1991 July 15-21 (7) 96.6 71.7 84.2  
           
*Lengthiest on record        

 

Another striking characteristic of July 2013's heat wave was its relatively small diurnal variation - average high and low were 15.6 degrees apart.  By comparison, most of the other heat waves among the twelve hottest had diurnal variations greater than twenty degrees.  (1991's was the greatest, at nearly 25 degrees.)  Meanwhile, the last two days of 2013's heat wave had diurnal variations of just 13 degree and 12 degrees (high/low of 96°/83° and 93°/81°).

 


New York's Lengthiest & Hottest Heat Waves

Heat_wave

 

A heat wave, at least in the Northeast, is defined by the National Weather Service as three days in a row with high temperatures of 90° or hotter.  They occur, on average, about twice each summer.  However, this post is interested in "big boy" heat waves, i.e., those lasting seven days or longer.  Since records began in 1872 there have been just twenty-two, with one occurring about every seven years.  The seven-day heat wave of July 2013 broke a ten-year streak without one.

 

  • 2013 marked the 60th anniversary of New York's longest heat wave.  Lasting twelve days, it was also noteworthy because of how late in the summer it occurred, from Aug. 24 to Sept. 4, 1953.  Twenty years later an eight-day heat wave occurred from Aug. 28 to Sept. 4.  Both had an average high of 95.4°, fifteen degrees above average.
  • The heat wave with the highest average high temperature was the nine-day heat wave of July 1977.  Its average high was 97.1°, thirteen degrees above average.  It was made famous by New York's infamous blackout which happened on the first day of the heat wave.  The high temperature on the final day of this heat wave reached 104°.

 

Heat_wave_map

 

  • The heat wave that had the "coolest" average high temperature was the one that occurred between July 5-13, 1944.  During its nine days, high temperatures ranged between 91° and 94°, averaging "only" 92.4°.
  • New York's first week-long heat wave was in 1896, followed by a second in 1901.  Then the next one wouldn't be until 1944 - and that summer had two. 
  • Besides 1944, three other summers have suffered (or "enjoyed", depending on your preference) through two major heat waves: 1953, 1993 and 2002.  Five weeks before New York's longest heat wave on record, the summer of 1953 also had one of seven days in mid-July.  1993's two heat waves (one of ten days, the other of eight) occurred between July 7 and Aug. 4.  And in 2002, there were heat waves of eight and nine days in the three-week period between July 29 and Aug. 19.

 

Heatwave3

 

  • Half of the City's major heat waves occurred in the twenty-six years between 1977-2002.  And while a seven-day heat wave occurs once every six or seven years (when all years between 1872-2013 are considered), between 1977 and 2002 they occurred every other year.

 

Hottest heat waves in NYC

 

 

Save

Save

Save

Save


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

Hot_fun

 

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%. 

 

Central_park_summertime

 

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.  

 

Coney_island

 

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%.)

 

Concentraiton of 90-Degree Days


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. 

 

 

 

Save

Save

Save

Save

Save

Save


The Heat is On: New York's "Hell Week", Hottest Week of the Year (July 16-22)

Flames

 

"Hell Week" refers to the time during the summer when New York City is most likely to have temperatures in the 90s.  The week beginning July 16 encompasses the three most likely days: July 18, July 19 and July 21.  Whereas the average day in July has experienced a 90-degree reading 29 times (since record-keeping began in 1869), July 18, 19 and 21 have reached 90° or hotter 45, 44 and 38 times, respectively (thru 2019).  And July 21 and 22 have had the most occurrences of triple-digit heat: six times on July 21 and four on July 22.  (And there's a mini-Hell Week between July 7-10, in which the average number of 90-degrees days is 33.)

 


Looking at the history of these dates reveals that July 18 didn't emerge as the date most likely to have a 90-degree reading until the late 1980s.  Before that, July 9, July 19 and July 31 were the dates that vied for bragging rights.  However, since 1980 60% of the years have had highs in the 90s on July 18 (including four years in a row from 2010-2013).  By contrast, before 1980 (going back to 1872) just 23% of the years had 90-degree highs.

 

90-DEGREE DAYS
   
  Daily Average
June 13.8
July 28.8
August 18.2
Summer* 20.3
Hell Week 36.2
   
July 16 35
July 17 34
July 18 45
July 19 44
July 20 35
July 21 38

*Note that "Summer" refers to meteorological summer, June 1- August 31.

 

Many readers may be surprised to discover that the two days most likely to see 90° has only a 30% chance in any given year to see temperatures that hot (i.e., 45 out of 151 years).  Perhaps it's because it's human nature to remember the days that are in the extreme.  Actually, even days in mid-summer have experienced long stretches without 90-degree readings.  For instance, there were no 90-degree readings on July 18 for twenty years in a row between 1923 and 1942.  And in the most extreme case, July 1 had no 90-degree readings between 1975 and 2011, a span of thirty-seven years.

 

Quizzical_look

 

Of course, as most New Yorkers are well aware, getting through "Hell Week" doesn't put us in the clear.  In fact, of twenty-two heat waves of seven days or longer, only a handful  have occurred in mid-July.  New York's longest heat wave on record, lasting twelve days, occurred between Aug. 24 and Sept. 4 in 1953.  The next longest, 11 days, started in the second half of July (July 23) in 1999.  And the third and fourth longest, both 10 days long, were in early August 1896 and early July 1993.

 

Chart - hottest hell weeks
   

 

Clipart_veryhot

 

I want to thank my fellow weather "nut", Eugene DeMarco of Queens, for helping me by supplying and organizing some of the weather statistics that provided the background material for this and recent posts.   

 

 

 

 

 

 

 

Save

Save

Save

Save

Save

Save

Save

Save

Save

Save

Save

Save

Save

Save

Save


Unbearably Warm Summer Nights in New York

Hot_nights_nyc_firehydrant

 

It used to be that New York's most stifling overnight temperatures in the summer fell into the upper 70s - but lows of 80° or warmer were few and far between.  However, this began to change in the late 1970s.  Since then, lows of 80° or warmer have occurred 38 times (thru 2020) - still infrequent, but no longer unheard of.   As Sandy and Danny sang to each other so famously in Grease, "Oh, those summer nights!"

 

  • Looking at the years from 1950 onward, only 1952 and 1957 registered 80-degree lows before 1978.  But since 1978, nineteen years have had lows of 80+.  To put it another way, there were no 80-degree lows in the twenty year period between 1958-1977, but they've occurred every two or three years since 1978.
  • The most 80-degree lows were experienced during the summer of 2002, when there were four.  Four other summers have each had three such stifling readings: 2013, 2010, 1988 and 1980.
  • The warmest low temperature, 84°, has occurred four times, most recently on July 22, 2011 and July 15, 1995 and twice during the summer of 1908.  (2011's high was two degrees hotter than 1995: 104 vs 102; both days in 1908 had highs of just 93°).  Interestingly, on the day of New York's hottest temperature on record, 106° on July 7, 1936, the morning low was 77°.  Therefore, July 22, 2011 is the day with New York's hottest mean temperature (94°).

 

84LumberLogo

 

  • With the exception of 1952, when an 80-degree low occurred on June 26, all other 80-degree lows have occurred in July or August.  The latest date for such a warm low is Aug. 30, 2018.  This broke the previous record, in 1985 and 1988, by 14 days.
  • The summer of 1995 reported the most low temperatures of 77° or warmer, eleven - one which was 84° and the remaining ten were between 77°-79°.  It was followed by 1999 and 2002, with ten.
  • The biggest rise in temperature on a day with a low of 80° or warmer was 22 degrees, which happened on July 10, 1993 (102°/80°) and was equaled on July 6, 2010 (103°/81°).  The smallest rise in the past 100 years is eleven degrees, which was reported on Aug. 30, 2018 when the high/low was 92°/81°. However, there have been seven even smaller variations in the years before 1911, with the smallest being seven degrees, which occurred during the summers of 1906 and 1908, both with a high/low of 87°/80°.

 

Chart - smallest diurnal variation on hot days
 

  • A low in the upper 70s or warmer doesn't guarantee the afternoon high will soar into the 90s.  There have been fourteen instances where the high has stayed below 90° (three of them occurred in 2015, two in 2016).  The two days that failed to reach 90° with the warmest low occurred on July 26, 1979, when the high struggled to 87° after a low of 79°, and on July 15, 2016 when the high reached 88° after the same low.  The smallest diurnal variation when the low was 77° or warmer was seven degrees - and it also happened during the summer of 1979.  On Aug. 4, under a thick haze, the high struggled to reach 84°.
  • Twelve years since 1950 haven't had a low of 77° degrees or warmer.  The coolest "warmest" low was 74° degrees, which occurred in the summers of 1996, 1976 and 1962.
  • Between 1950 and 1977 the typical year had twenty-eight days with lows of 70° or warmer.  Since 1978 the average number of such day has risen to thirty-seven.  The most was 60 days in 2005; the fewest was eight in 1962.

 

80-Degree Lows
(1950-2012)    
  Daily Minimum Temp
Year 80+ 77-79 Total
2002 4 6 10
2010 3 5 8
1988 3 5 8
1980 3 3 6
2011 2 2 4
1999 2 8 10
1993 2 2 4
1952 2 2 4
2006 1 5 6
2005 1 6 7
2001 1 3 4
1995 1 10 11
1985 1 2 3
1982 1 1 2
1981 1 4 5
1978 1 1 2
1957 1 1 2

Note: Chart does not yet include 2013's three 80-degree lows, 2015's one or 2016's two.

Save

Save

Save

Save

Save

Save


Today in New York Weather History: June 18

 

1967

Today was Father's Day, and after a seasonably warm and dry day, flooding rains dumped 1.83" of rain in the two hours between 9-11 PM.  Rain continued through mid-afternoon on 6/19, at much lower rates, totaling 3.18".  This heavy rain was attributed to a tropical depression that moved up the coast.

1995

It was a sunny and hot Father's Day as the high reached 90°.  This was also the first 90-degree day of the year, the latest date for this occurrence in ten years (it typically occurs at the end of May).

 

Fathers.day

1997

During a thunderstorm, 0.36" of rain fell in just five minutes time between 12:05-12:10 AM on 6/19, and 0.64" fell in fifteen minutes between 12:04-12:19 AM.  Because the National Weather Service doesn't recognize Daylight Saving Time, and uses Standard Time year-round for its records, this rainfall was credited to 6/18.

2006

Similar to 1995, today was Father's Day and the high of 91° was the first 90-degree reading of the year.  (The next 90-degree reading on Father's Day would be in 2018.)

2009

2.30" of rain fell today, a record for the date.  Rain fell until 5:30 PM, preventing the afternoon temperature from getting higher than 64°, sixteen degrees below average.  Today's rain brought the month's total to 7.61", making this the rainiest month since April 2007.   

2014

Although this year's meteorological summer (June 1 thru Aug. 31) would have eight days in the 90s, today, with a high/low of 89°/76°, saw the warmest mean temperature of the year until Sept. 2 (which had a high/low of 92°/77°).

2017

It was a sultry Father's Day, with the dew point in the low 70s throughout the day, peaking at 74° early in the afternoon.  Combined with a high of 85°, the heat index reached the low 90s.

2018

Yesterday and today both had highs of 91°, but there was a distinct difference between the two days in terms of comfort level as today was much more humid.  As a result, today's heat index rose to 96°, which was nine degrees hotter than yesterday (this afternoon's dew point was in the low 70s, while it was only in the upper 40s yesterday).

 

What a difference a day makes
  

Save

Save

Save

Save

Save


Looking Back at New York Weather: June 16

 

1967

With a high of 96°/71°, today was the hottest day of the year.  The high was one degree shy of the 1891 record.  This was the fifth June in a row to have a high of 95° or hotter - the longest such June streak on record.

 

Overheated car

1981

Today's high soared to 93°, the first 90-degree day of the year.  This was the latest date for the summer's first 90 since 1963, when it occurred on June 24.  (The typical date is in late May.)  Besides the heat, there was unbearable humidity to contend with as the dew point in the early afternoon reached 80°, producing a heat index of 109°.  In the years since 1950, this dew point is the highest on record for Central Park.

1982

After a warm and sticky day, with a high/low of 87°/68°, thunderstorms moved in after dark.  The rain came down heaviest between 11 PM-1 AM when 0.58" fell.

 

Clipart_thstorm

1985

Today was Father's Day, and rain fell overnight until 7 AM, and then a thunderstorm moved through between 7-8 PM.  In total 1.19" of rain fell.

1988

This was the fifth day in a row with 90-degree temperatures, the longest heat wave since one that lasted seven days in July 1983.  The average high during these five days was 93°.

 

Tropicalheatwave

1989

0.21" of rain fell tonight, bringing the total rainfall in the past eleven days (since June 6) to 7.16".  Additionally, low temperatures between June 9 and today were all in the 58°-60° range; (average low during this is in the low 60s).  High temperatures, however, ranged between 61° and 84°.

1990

For the third day in a row the low temperature was 60° (three degrees below average).  High temperatures, however, were very different: 68° on 6/14; 81° on 6/15; and 85° today.

1991

It was a miserably hot and humid Father's Day.  Under hazy sunshine, the day's high/low of 94°/76° was fifteen degrees above average.

 

Clipart_sweating_thermometer

1998

Today was the first 80-degree day of June (after there were ten May), as well as the first day this month with an above-average mean temperature (+3 degrees).  This was the latest date for the first 80-degree reading since 1916 (when it occurred on June 18).

Save

Save

Save

Save


Today in New York Weather History: June 15

 

1933

Less than a week after a record high of 97° (6/9), this morning's low of 48° was half that temperature, and also a record.

1971

Showery (0.32" fell) and cool, with a high/low of just 60°/56°.  The high temperature was nineteen degrees below average and more in line with the second week of April.

1974

High temperatures of today and the previous three days: 79° (today)-78°-77°-76°. 

1983

Today's high was 92°, the fourth day in a row with a high in the 90s.

1988

For the second day in a row the high reached 96°.

1989

Overcast skies, AM drizzle, and winds off the ocean resulted in just a three-degree difference between today's high (61°) and low (58°).  The low was five degrees below average, but the high was 19 degrees below the norm.

1994

Today's high reached 96°.  This was the first of four days in the next 30 days with a high of 96° or hotter.

1998

Today was the fifteenth consecutive day with cooler than average temperatures.  During these days high temperatures ranged between 65° and 73° (average is 78°).  This made the first half of June six degrees cooler than average.

2014

Today was Father's Day, and if you forgot to give your Dad a necktie there was no need to fret since the weather was enough of a gift as skies were mostly clear and the afternoon temperature rose to a seasonable 80°.  Today's low of 59° was the third, and last, day with a low in the 50s this month, the fewest since June 1996 (which also had three, all in the first three days of the month).