IÂm having a similar problem. I find when the weather is humid, and hot, it gets worse. In my case, the grass lays over on itself in some areas, and eventually ends up killing itself off, and the lawn gets bald patches. IÂve got quite a bit of shade, so that factors in there, too. I find once the weather cools off, and the air dries out (and we get cooler over night temps) the grass grows much better.

Usually, every year we end up seeding a few areas that have died off, but this year weÂre experimenting to see if they fill in on their own. Some of the areas are filling in already. You could wait and see if this happens once your weather cools off.

Also, you should make sure the lawn is getting enough water (weÂre not getting any rain, either). I make sure to water deeply once a week, if we havenÂt gotten a good amount of rain  I think the recommendation is 1", once a week.

dgs9r, my first thought was 'grubs'; a bad attack and you can roll up the turf rather like a carpet. A fungus like "brown patch" will produce similar symptoms but the blades will feel damp and limp....unless this happened and now the blades are all dried out. You can check for grubs by digging down to 12 inches or so to ascertain the presence of the insect. For other insects do a soap flush.
In each case sample the area where the grass is turning from green to not-so-green to dying. If you eliminate insects, and presumably you have eliminated environmental causes (oil spill, pool overlow), then that leaves a cultural practice like weed control or fertiizer application. Review the recent history of events on your lawn and you will deduce a 'probable cause'.