Hot weather and the 4th of July seem to go hand-in-hand. And hoping for sizzling temperatures on that day is on par with dreaming of a white Christmas. However, like snow on Christmas, a 90-degree reading isn't all that common in New York City. In the years I've lived here (since 1979) it's hit 90 just eight times on this holiday, about once every four years.
One of the eight July 4th sizzlers occurred last year (2010) when the afternoon high in Central Park topped out at 96, tying 1999 and 2002 for the distinction of being the hottest July 4th. However, if the low temperature is considered as a tie-breaker then 2002 was the hottest overall as the morning low that year was a sultry 81 while 1999's was 79 and last year's was a relatively mild 73.
New York's hottest 4th of July of all time was in 1949 when the mercury soared to a sizzling 102. FYI, NYC's hottest temperature of any date is 106, occurring in 1936 five days after 7/4. A few July 4ths (again, in the years I've lived in NYC) have been the 1st day of prolonged heat waves. In 1993 every day was 87 or hotter between July 4-18, with 13 days in the nineties, including three consecutive days of 100+. In 1988 another prolonged hot spell lasted 17 days between July 3-19. All days but one were 88 or hotter and 11 were 90+. Last year between July 4-7 every day was above 96, including 103 on July 6. (July 2010 tied July 1999 as NYC's hottest July on record.)
While on the subject of hot weather let me leave you with a few more statistics: July 18 is the day most likely to have a 90-degree reading. Since 1979 it's happened 17 times on that date, so in any given summer there's a 50/50 chance it will reach 90 then. And 100+ readings have been experienced during eight summers over the same period, including the past two summers.