It's really hard to average that high over a month because all it takes is a few days below average and a bunch of days near average and then even if 20 out of 30 days were a decent amount above normal at night your average gets dragged down.
The latest average low in July at LGA is 72.
For example if you have 5 lows at -2 departure , 5 days at 0 departure, 10 days at +3 departure and 10 days at +5 departure, even though most lows were very warm the whole month's lows comes out to +2.3 degrees.
Central Park's average July low is 70 so for them it's significantly harder to have any monthly average low of 76.
LGA is currently 73.2 degrees for the average monthly low despite the heat.