That looks like any grass that's getting too much water.

Part of the problem is the roots. The grass may have developed some major roots during the rain, but since it was raining so frequently, those roots might not be very deep yet. It is St Augustine, so it will not die away if it dries out. This time of year in your area a mature St Aug lawn should be deep watered no more than once every 2 weeks. In Sept we suffered through almost 19 inches of rain. I don't anticipate having to water again this year. If we get a seriously dry front with low humidity, then maybe I'll have to water next month. For you, you have to ensure you water very deeply and back way off on the frequency. This approach will cause the grass roots to dive deep looking for moisture. I realize you're in FL where everyone waters every day, but you'll have to trust that this works. Here's more.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.

Wow thanks so much for all this helpful information. It takes 2 hours for my sprinkler to spray 1 inch, I was watering for only an hour before. since it is mostly in the 80s lately I will water biweekly until it gets colder. Again thank you so much for taking the time to respond.

Let us know if it improves.

If you're in/near Jacksonville, it's not getting too much water. We've had very little rain in the past six weeks. We had a record high of 91 today and we're headed for another record high tomorrow. I suspect chinch bugs and/or sod webworms. You should not apply fertilizer in October other than perhaps a potash to strengthen the roots.