Why has the average low for the hottest months in Clearwater Florida about 5 degrees higher than the historical average?
What you are observing is called anecdotal weather observations.  I will address it in a number of points, none of which many people will agree with, but so be it.

2-3 years is weather, not climate.  Climate is measured in millennia, not days.  Historical averages are measured, well historically, which for most locations in the US is 50-300 years.  During those years, methods of measurement have changed, so historical numbers may also have glitches in them, such as the the highest US temperature ever recorded is still in dispute because of how it was measured.  But historical averages are calculated from all of those years, ones with droughts, unseasonable cold fronts, and so on.  Warming patterns which are the basis for global warming studies are based on looking at all this data, plus many years of indirect data from ice cores, tree rings, sediment deposits, and many other sources, not from 2 years of personal study.

It is routine to have years that are outside of the average, that is what averages are.  It is also human nature to amplify the variation and see extremes.  I did not go that far back, and I used only one source, but I looked at a little recent recorded data for Clearwater.  I took daily numbers and went with variations to the daily average temp for that date.  For Aug 2017, there are 8 days available thus, and the daily lows have been recorded as +17 degrees to average, or +2.15 degrees.  For 2016 back to 2013 you get +27, -2, +24 and +7 for Aug, or as an average daily difference about +0.87, -0.06, +0.77 and +0.23 with a average for the 4+ years of +0.38 to average.  Only the partial month for 2017 exceeds 1 degree variance to average.

July numbers are, starting with 2017, 41, 37, -29, 13, -31 or in daily variations +1.32, +1.19, -0.94, +0.42, -1.00 for a 5 year average of +0.20.  Although the last two July's have exceeded the plus one degree variance, two of the prior three were almost the opposite.  That is weather and normal variation.  To get to climate numbers requires looking at those patterns over centuries, not over a couple years.

Trust me, I am not refuting global warming.  I am however refuting using such anecdotal observations as a bases for the claims.  Weather patterns work in cycles, and before climate change claims can be made the cycles must be accounted for.  When a location has an especially hot day, or month and references are made to global warming, it make that side of the argument look silly.  When a blizzard occurs, there is a record low, or an seemingly especially cold day, and the deniers point and chant global warming and laugh, they may also feel they scored points, but under statistical analysis they look silly as well.

I do not claim the above to be a statistical analysis.  I also did not cherry pick data, I simply only had time or willingness to do a quick 5 years.  That was more than enough to see yearly variations and demonstrate that a perceived variation of 4-5 degrees is actually 1, and 1 degree is still within typical yearly variation.  To make a real claim requires a pattern of trending real variation in a continuing upward direction and that require rigorous and systematic data collection and analysis.