Plotting the normal temperatures and sunshine hours for a location places that location in a particular 2-dimensional space. I demonstrated that in these charts. @turfstuf suggested that a diagonal line might show a break point for classifying warm and cool-season grasses.

@asianturfgrass Looks like a blurry line drawn from 14h to 35C might show an over/under for some warm/cool grasses & growing seasons.

— turfstuf (@turfstuf) April 16, 2016

The idea is that the top right would be warm-season, the area around the line would be transition zone, and the area to the bottom left would be cool season. That chart looks like this.

I agree that different regions of the chart are indicative of over/under points for different grasses or growing conditions. I wouldn't separate by that diagonal line. Here's the break points I would use.

• mean annual temperature less than 15°C, cool-season
• mean annual temperature from 15 to 20°C, transition zone
• mean annual temperature above 20°, warm-season

For those general breaks, one can estimate the annual mean from the monthly charts, or plot the locations by the mean annual temperature.

Continuing with the breaks, specifically looking at which warm-season grasses will be suitable:

• within warm-season, and more than 6 hours sunshine per day, bermudagrass
• within warm-season, and less than 6 hours sunshine per day, zoysiagrass or other warm season grasses that are tolerant of low light conditions: bermudagrass will struggle
• within transition zone, and less than 6 hours sunshine per day, if warm-season grasses are used, zoysiagrass or other warm season grasses that are tolerant of low light conditions: bermudagrass will struggle

A transition zone location like Atlanta looks like this when those points are marked on the plot.

Two warm-season locations, one where bermuda thrives (Honolulu) and another where bermuda is overgrown by more shade tolerant grasses (Hilo), are shown here.

In the next plots I show some other locations: cool-season, warm-season, and transition zone. The break points I use seem to agree pretty well with grass distribution and performance around the world.