Okay I think I know what you’re saying. Heat index only encompasses temp and dew and those are both measured in full sunshine albeit with proper shielding.
You want something that factors in temp, solar radiation, humidity, and wind. There are equations to calculate that, but you’re not going to get it on an ASOS without a pyranometer to measure the solar rad. Davis uses an equation to calculate THW index or THSW index if you have a solar sensor so I can do that here. But it changes wildly during the day depending on clouds and wind speed.
Here’s my THSW index chart for the day. You can see where the sun started hitting the solar sensor and each cloud we had.