This is a very perceptive way to watch time pass when watching nature—and definitely useful when life revolved around things growing in the groud. I wonder how much drift there is on the dates given, or if local climate yields highly predicatable weather patterns. For example here in the South-East US, the "last frost" date can vary from mid February to late April but our weather patterns are higly variable.
August 8–12 涼風至 Suzukaze itaru Cool winds blow
When early August anywhere in mainland Japan more closely resembles Satan's armpit, with extreme heat and humidity and a distinct lack of cool breezes.