Why is it cooler when the sun just comes out and hotter at noon?

Surface heat comes from solar radiation, but directly from ground radiation. At night, ground radiation is the source of surface temperature, but it will be gradually lost without the supplement of solar radiation. When the sun comes out in the morning, the ground radiation is not fully supplemented, and it is cooler every morning.

By noon, especially at 12 local time, the solar altitude angle is the largest, the solar radiation is the strongest, and the ground radiation is the biggest supplement. By 2 pm, the ground radiation released a lot of heat, so the local time 14 was the hottest.