Making sourdough bread in a warm and humid climate

If your starter is tripling in 3 hours, it's unlikely that you need to add additional yeast.

If the humidity is causing your dough to spread as it rises, you could try slightly lowering your hydration to account for moisture in the air. You could also add a fold in your bulk ferment time to give more gluten strength.

You don't mention how long you are proofing your loaves, which could be very important. Generally sourdough will need several hours at a moderate temperature to rise properly. Be sure you aren't rushing to the oven. (When you poke a loaf, it will gently and slowly spring back when it's ready.) This may mean that you will need to proof in the refrigerator, basement, etc to keep your loaves cool as they proof.

Finally, if spreading continues to be a problem, adding some vitamin C powder (ascorbic acid) can help get more volume in your loaves. This works by making the gluten tighter, so use it sparingly. It is especially beneficial in whole grain sourdoughs.

It's almost impossible to diagnose your baking problem without knowing your recipe, method, and skill level, but I'm going to have a swing at it anyway! :)

First, make sure you're using the right kind of flour. Do not use whole wheat pastry flour, bleached flour, or cake flour. These will all cause problems. You'll want to use good, *unbleached *all purpose or whole wheat flour with a protein content around 12-14% (check the label -- 3 or 4 grams of protein per 30 grams of flour). Even better: check the ingredients for hard red winter wheat. Don't use anything that says soft wheat.

Second, unless you're confident in your recipe (i.e., you've made it before successfully), I would recommend sticking with white flour at first. It's much more forgiving than whole wheat, and once you gain confidence, you can start to substitute whole wheat a half cup at a time.

Third, really keep an eye on things during the proofing stage. When I make sourdough bread, it takes about 2-2.5 hours at 65-75 degrees. If your house is 85 degrees, you may need to reduce this to 1-1.5 hours. Or, like sourd'oh suggested, proof in the refrigerator. In fact, I've had great success with doing the final proofing overnight in the fridge. I don't even let it warm up when I bake it -- just throw it straight into a hot oven!

Finally, if the recipe you're currently using continues to give you trouble, try another one! My favorite resource when I was learning to bake was The Fresh Loaf forums. In fact, there's a reliable whole-wheat sourdough recipe there that you might want to compare to your own. There are also a number of excellent modern baking books to consider, including Peter Reinhart's Artisan Bread Every Day.

Best of luck baking!