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°.
- 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.
- 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.