Big Bend National Park

That part of Texas is our favorite. Check out Alpine, Ft. Davis, and the Ft. Davis state park. We have enjoyed Alpine and stayed at the Lost Alaskan RV Park. Great owners and facilities. About the distance to everything--everything will be a good drive to and back regardless of where you stay--and in BBNP the speed limit is 45 mph! But enjoy it all. Also check out Big Bend Ranch State Park on the Texas Parks and Wildlife website--no RV camping but a really interesting place. McDonald Observatory star parties are very good--hope there is no moon. Take note, the road into the Basin in BBNP has restrictions on trailer length--I would just not take a trailer up that road! IT will be HOT in September--probably over 100 most days but can cool down after sunset.

I'm there right now - it's 5:07 p.m. and it's 85° - my RV thermometer says 100°, but it's laying on the outside black step in the sun!!!! It doesn't get cool in Oklahoma till October, so my bet is that it's still pretty hot here in Sept.

That said, we're staying in Terlingua, which is nice access for both parks (state & nat'l), but if I had my druthers, I would have stayed at Rio Grande Village (full hookup). They have internet, no TV and full services, AND you back up to the river where a breeze off the river can feel a little cooler (I'm not going to say cool, cause I doubt much is cool that time of year). But it's a birder's paradise. The bad news is that you're a distance from everything, at the other end of the nat'l park from the state park. But if you want to be in the center, I recommend where we're staying - it's easy to get to and nice - full services (except they don't have cable anymore - can't get their cable to work, they "have" the hookups, it's just they are snowy reception).

Also a lot of the park closes for the summer, so check to make sure places will be open.

Star parties are nice here, but if you stay up at Davis Mts. State Park (make reservations first), you're a hop, skip and a jump from the McDonald Observatory where they have fab star parties with their 23" scopes and other scopes on all sorts of great objects in the sky. See our blog for the review on our evening there.

You should not have any reason for A/C at night to sleep. It is somewhat high elevation & it will most likely cool off at night, perhaps needing an extra blanket or two. Maybe a little heat to warm it up in the morning at times.

It could be warm, but it could be cool durning the day. Depends on what the current weather might bring. A high pressure, it could be warm, even hot. Low pressure, could be cool, even cold. If rain happens, it will be much cooler.

What I have on :)Big Bend Area. We really enjoyed Balmorhea State Park & checking out Fort Davis Nat'l Historic Site. These are north of Big Bend & of Alpine. Balmorhea is at a lower elevation, Fort Davis a high elevation.

Depending on your camping style & preference as well as climate conditions when there, you could choose which campground you want to stay once you get there. I see no need for reservations. Can't see it being too full at that time.

I see you're from Georgia with high humidity so Big Bend will have DRY heat. :) The place for you to stay is in the park at Rio Grande Village full-hookup park. (There's a dry camping area right next door with the same name.)

You will probably want to start your day very early and take the afternoons for relaxation time. The evenings will be very pleasant.

There won't be any crowds to contend with which will be great. If this is the only time you can go it's better than not going at all. Have a great trip!

Likely it will still be quite warm/hot in the lower elevations: Rio Grande Village, Castolon and at many of the roadside sites. Chisos Basin might be ideal, but it could be hot there too. We were in the Basin in mid-September several years ago and wished for air conditioning every day. Nights, though, will cool down nicely throughout the park.

http://forecast.weatherdb.com/l/79834/Big-Bend-National-Park-TX

This may help you a little bit about the past. You will have to click on monthly average.

You're going to want to make sure you can use your A/C. It can still be pretty hot in mid-September. The campgrounds run by the Park Service don't have any hookups. Cottonwoods has a no generator policy. The only place you can get full hooks are at the Rio Grande Village in the commercial campground. They have about 30 spaces on a paved parking lot. You may want to make reservations.

Alternatively you can stay at one of the many commercial campgrounds in Study Butte just outside the Park on 118. You'll probably want a toad to visit the Park. A 4-wheel drive is best because there are a lot of roads you can take then to follow the river or visit old town and home sites.

Here's their contact info. They can give a more accurate idea for your question.http://www.nps.gov/bibe/contacts.htm

BBNP is a fantastic destination. In March we attended a star party (astronomy gathering) there and did the river trip. Loved it.
Here's info on their star gazing program. They have very little light pollution. http://www.nps.gov/bibe/planyourvisit/stargazing.htm