I’m traveling with my family in the Outer Banks. It’s quite an elevation change compared to Pisgah, where we were last week; but, that is part of the compromise that comes with family vacation. Anyway…it’s hot here! And, there’s no shade whatsoever. I thought if I got out early enough, the temperature wouldn’t be brutal. Turns out that by 9am, it’s in the high 80s with 78% humidity. I’m working through the sweet spot 2 plan (I had to take a few steps back after having a nasty respiratory infection that derailed things for a bit). Today called for tempo efforts. Wow! They were hard! I felt less like a cheetah, and more like grumpy cat. I struggled with hitting my power numbers, falling a few watts short with each interval. My heart rate was crazy high. And my perceived exertion was level mega struggle (I think that’s the scientific term). Before I beat myself up as I spend the afternoon sitting on my butt at the beach, is it appropriate to blame the weather, the heat and humidity, more so than my fitness? Sure, my training has been a bit interrupted with being sick and traveling. But the other day, I did a 40 mile gravel ride with 5,500 feet of climbing followed the next day by a 20 mile mtb ride with 2,700 feet of climbing. My legs were sore-ish, but I felt strong overall. So, how much does heat and humidity affect power output and heart rate? Is there a good article/research (I’m a nerd) that might put this in perspective? I’ve consulted coach Google, and what I learned seems to confirm that it’s the weather not me. But, we all know the shortcomings of coach Google, so I figured I throw it out there to the real experts. Thanks!
Hey!
With an elevation change your watts are going to be harder to hit, specifically if you’re higher than normal! So don’t be discouraged.
With the Heat and Humidity- you’ll also be effected. I live in Birmingham, AL. I ride at 5:30AM in the summers for heat and humidity sake and I have to push through the workout because the temps/humidity level play a huge role. It’s not easy!
Be sure to include electrolytes and salt during your training rides! It will help. You could also sip on electrolytes throughout the day/night to ensure you’re getting enough hydration!!
Hope this helps!
-Coach Allie
Coach Google 
Think you said it the best: it’s the weather not you. This is why working out in the morning is #1 of the seven habits of successful masters cyclists 
We have a saying in the Richmond VA “Humidity Zone” 
If you can hit your numbers when the real feel is 105F then in early fall, you fly!
It’s the weather. Your fitness is fine.
Alex Hutchinson reviews a study of supplemental heating training for cyclists and runners that found significant performance benefits. As an aside, I found indoor trainer heat training to be miserable but seemingly helpful in preparing for Mt. Washington. How to Heat-Proof Your Training | Outside Online
Agree with what was already stated: it’s the heat not you. I’ve had the same experiences as you, then a few days later when temps were cooler had minimal difficulty holding my target power numbers. Heat. It’s brutal.
Coach Google is the husband of Dr. Google. They both are really good with spreading information that increases anxiety levels 
Thanks for all the feedback! Now, if I could only get out of bed before 5:30. Ugh.
Just got home from vacation, and Connecticut’s weather is as miserable as the South! I swear Asheville has the perfect weather. Wish I had more time there. Anyone live there and want to give me a job?!
As someone who lives in the south, yeah getting out real early gives you the best temps, but the humidity is thru the roof, >95%, if you go late in the day and the temps are way high, but the humidity drops a bit to 80%. I’ve found the best time is to go at 9-10 am for intense work- you still get lower temps, the sun is not yet right above (you still get some shade) and the humidity is dropping a little. Nothing worse than doing intervals and you pour sweat every wear, but it does nothing becasue its too humid to evaporate. To me 70 degrees and >95% humidity is just as bad as or worse than 90 degree temps