Neighbors neglecting dog in heat

I am looking for advice. From my rooftop patio I can see into my neighbor’s backyard. Over the last couple weeks I’ve observed that they are regularly leaving their full grown pitbull in a kennel on their patio. I’m not sure how long this has been happening. I’ve only just noticed.

The kennel is very small for the dog. I can’t see any water or food in there with it. The dog is out there for hours at a time. I get home at 3pm and I’ve checked and it’s in there at that time and I check before bed at 9:30 and it’s still in there. The dog looks to be a good size, so not starved. The patio where the kennel is has shade. However, I’m really scared about the heat and the prolonged time they’re leaving the dog.

I am nervous to interface directly with the neighbor because: 1) I would need to admit that I was looking in their private area (even though I have clear view from my own home) 2) They don’t seem like very kind people. I’ve seen them arguing with others before so I’m nervous about a volatile reaction no matter how kindly I bring it up.

I don’t even mean to be hateful to these people. I am just very nervous for the dog. I really strongly don’t believe I’m being a Karen here and there is a real cause for concern.

Do I write an anonymous letter to the neighbor? Do I call the humane society or something?

What do y’all recommend? Please help!