Well just looked up the conditions for that night. The air was a little thing, calcs out to 1600 feet.

http://www.modulardepot.com/density.php It calced out too

Based on:
Temp: 80°
Humidity: 76%
Track Altitude: 50 feet
Pressure: 29.95 in.


Density Altitude = 1716 feet ET MPH
Uncorrected 14.6 @ 97
Corrected 14.32 @ 98.84