Hot days really don't come into play for me... I workout early in the morning, and my workout area is in my basement which is generally pretty cool. That said, I'd recommend trying to work out early in the morning if you can, before the heat gets too much. And either way, have plenty of water available & drink it throughout your workout.
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So I've finished up the first week of Les Mills Pump, and here are my impressions so far. You start out with an instructional video called Pump Basics, where you learn about proper form for all the lifts along with the philosophy of Pump, which they call "the rep effect". This simply means low weight, high repetitions, which they claim leads to longer, leaner muscles. Sagi Kalev of Body Beast posted on Facebook recently that low weight, high rep is "the stupidest thing ever", but he's biased towards bodybuilding and he may be right as far as bodybuilding goes.
The first real workout is called Pump Challenge. It's about 25 minutes and feels very introductory in nature -- they walk you through each move, explaining proper form. There are different sections -- squats, chest & triceps (presses & triceps extensions -- they do these on the floor but I used my bench), deadlifts & rows, clean & press, lunges, and shoulders. Each "track" uses a different trainer, and they demo each move before you do it. Everything is in time with the music. You do each move at different tempos -- 4/4 count (up/down), 3/1, 2/2, and finally "singles". With lunges, they also do "bottom halfs", where it's basically 3 low pulses, then extension. They also have 3 recommended weights for each track (beginner, intermediate, advanced), and give you time to switch weights. There's always one trainer doing a modification. It's a workout that can be super easy or really tough, depending on the weights you use and your range of motion. You do this workout 3 times in the first week.
There's a 25 minute "Flow" workout, which is basically yoga. It's decent, probably a bit elementary compared to some of the P90X series yoga workouts, but it did have a couple twists on some familiar moves.
The last workout of the week was Hard Core Abs. Also around 25 minutes. It's not the hardest abs workout I've done from Beachbody, but it did actually have crunches in it and I definitely felt it afterwards.
They also schedule 45 minute walks on Flow and Hard Core Abs days.
Rest days are irregularly scheduled. The first two weeks include two rest days, afterwards there's one per week and it's not the same day every week. Today (Day 7) was a rest day, but I did PiYo: Sweat instead.
I definitely feel the workouts in my lats, back, legs and shoulders. So far, so good!