Analyzing the interval from June to December based on the given points:
- June: 0.2 inches
- July: 0.45 inches
- August: 0.55 inches
- September: 0.7 inches
- October: 1.6 inches
- November: 2.4 inches
- December: 3.2 inches
From June to December, the average rainfall is consistently increasing.
Thus, the correct response is: the average rainfall increases.