Andy by coincidence that’s almost exactly the same temp and humidity it was here in Canberra today and I did a 40km (no load) ride with a group. No flats:) But  I did feel the heat more than usual. 
We are experiencing unusually high humidity here. Tropical conditions. 

Other than air temp and humidity, radiant (reflected) heat from local structures can make cycling feel uncomfortably hot. Hotter than the official records indicate. 

Lack of shade, large areas of asphalt and concrete, buildings which absorb, build up and then reflects heat. 

It can replicate pizza oven conditions. I felt this type of heat in Tokyo. And in London in the 2022-23 summer. Indian-Summer conditions. 

Hi Andy,

I've had heat stroke four times in my life two of which were in SE Asia and one in the Himalayas.  One was when I was about 14.  I have determined that I've been extremely lucky to have survived since heat stroke is incredibly dangerous.  I have also determined that I will not survive another episode.

I haven't read every word of the comments on this forum but I sure haven't seen anything about electrolytes yet.  We buy packets of electrolytes at 7-Elevens here in Thailand and since I've been dumping a packet per day in my water bottles I have not been even close to a heat stroke episode.  

If you can't find electrolyte packets then drink the juice of at least one coconut per day because it is also filled with electrolytes.  

Electrolytes are probably the most important thing you can do.  Of course you should also drink lots of water but that won't prevent you from getting heat stroke. 

Besides all of that you should also not be covering up so much.  I use loads of sunscreen with at least 20% zinc.  Zinc pretty much cuts out the sun's rays for me.  Wearing less is better and the clothes I wear are very loose fitting.  Cotton is fine if it's loose.  Clothing with SPF 30 or 40 are great and also have wicking capabilities.

Good luck.   Believe me, you do NOT want to get heat stroke so please be careful.   

Hi Bruce, Coconut water sounds good to me!   I rode from 7am to 4.30pm today, with stops, and coped much better than earlier days.    Thanks for your comments. Andy

I’m going to expand on Bruce’s heat stroke information. I was with him for two of those and it’s very frightening. I’ve approached heat illness myself. If you start feeling dizzy or faint, seek shelter immediately. Cool yourself with a tepid shower and air conditioning. And if it’s getting worse take Tylenol or ibuprofen to cool down your core. 

The heat in SE Asia has been several degrees above normal. We finish riding by noon. Stay safe!