It's may. You guys are talking about night time vs. daytime temps? "it will be 55 tomorrow" (that's the night time temp though), and "but a few days later, it will be higher than average" (quoted from one of the replies)

The point I'm making is that you're in Tampa. You're right near the gulf of mexico, which has a certain temp. At night, if it isn't completely overcast, the heat rises from the land, and if there's any wind, it affects the local temp based on the temp of the water.

Dare to compare?
Here:
[link to www.climate-zone.com]

Average May max is 87.2
Average May minimum is 67.5

The thing about averages is that they take a whole slew of history and construct averages based on the history. It would take many years to raise the average because of all the prior history of florida (though this really goes for anywhere that records the weather).

Averages are the total of the units added together divided by the number of units (in this case, the number of days, both the highs and the lows)

ie:
40 degrees at night, 80 degrees in the day
50 degrees at night, 90 degrees in the day
55 degrees at night, 75 degrees in the day

this would average to:
145/3 degrees at night and 245/3 in the day
48.3 degrees at night, 81.7 degrees in the day

Oddly enough, even with that average, there were days that had higher and lower aspects of both the highs and lows.

I used to eat at Acropolis down in Ybor in the evenings and enjoy smoking hookah. Even in more decent months it could get relatively chilly when the sun went down.