Now that I've been riding in the winter for a couple years the summer heat has been hitting me harder. I used to be able to ride easily up to 100F, now 85F is about my limit. Feels like its harder to acclimate to the heat, or maybe I'm just getting older.
Acclimating to a higher temp is hard for me to. Its easy in the fall I just leave windows open at night. Then comes spring. I'm sure not going to raise the heat in my house just to acclimate my body.
I think you'll be fine in just few short weeks. Just keep in mind that it still gets a bit chilly at night this time of year, this could be a factor with up and down temps. Keep the faith in just a few weeks you should be fine.
After riding below freezing for several months this winter for the first time, you could say I've been spoiled by not having to deal with heat. So far this year, my answer has been to ride earlier & earlier in the morning when it is the coolest. Most of my rides are done by 9am lately, with some rides getting home by 6am when I knew it would be hot. I don't think I've even ridden in 80F yet this year.
I am really being a wimp about the heat. I remember just last summer thinking that 80F is perfect cycling weather and it made me sick to ride in 50F. Now I'm completely opposite. Granted, I've got a stockpile of clothes for every temp down to 10F, but I can't believe how much my mindset has changed. Hopefully I won't get many days this summer where the temp doesn't dip below 80F at night.
I like the heat but I won't ride in temps. over 100 any more. We rode on a 105F two summers ago and came back slightly dehydrated. I finished off 3.5 - 100 oz Camelbaks of Gatorade (75% mix), 3 straight 32 oz gatorades, 2 - 16 oz Cokes and 2 - 28 oz water bottles (I'd been using them for dousing myself all day but drank two). None of my party had to use the bathroom over 97 miles (we cut a 106 mile ride short). Temps were predicted for the high 90's not 100's. When we got to the 55 mile mark at 10:30 AM and it was already 96 we knew we were in for a long day. That's our official ride from Hell.
What I've learned and use (I ride in the Pine Barrens of NJ, it gets hot and humid here) is that instead of taking a sip take three or more. Always have fluids, no fluids then get off the bike and call someone. Dehydration means that I'll be weak/sick for the next three days. Warm water from a water bottle feels cool on a hot day. Humidity is worse than the heat. Once you've gotten heat sickness the rest of the summer you will have trouble with the heat in general (I don't know why that is). Sun Block beats sun burn bring the sun block with you and apply it ever two hours. Cold shivers is a bad thing on a hot day. Sitting with cars at a light on a hot day can make you sick (hang back away from the exhaust and heat of the cars).
The worst case of dehydration I've ever witnessed (it wasn't me) was on a double century. The night before this individual tried a new suppliment (against our rules of no dietary changes for 2 weeks before this ride). One of the side effect was the runs. We stopped every 20 miles so he could go. By mile 100 he wasn't looking too good but he wouldn't get in the SAG. We stayed on him to drink and eat and he did but not so much while riding. By mile 187 he was so far out of it he doesn't recall me asking him if he wanted me to call the SAG. I remember him giving me a big F*** **U look and he was still keeping the pace so I let it go. After the ride he doesn't remember that conversation and he was sick for 3 months with kidney problems.
Getting sick from the heat means you'll probably ruin the rest of your summer season.