https://icmglt.org/opinion-this-is-what-its-like-to-witness-a-nuclear-explosion/

"About 30 or 40 seconds after detonation, I took off the goggles and
watched the angry violet-red and brown cloud from the fireball.

As the rising cloud started to form a mushroom cap, I waited for the
shock wave to arrive. In the distance, I could see a long vertical
shadow approaching. I instinctively opened my mouth and moved my jaw
side to side to equalize pressure difference across my eardrums, closed
my eyes and put my hands over my ears.

Pow!

It hit me like a full body slap, knocking me back. I opened my eyes to
see another shadow approaching from a slightly different direction. Over
the next few seconds, I felt several smaller blows created by
reflections of the pressure wave off distant islands.

The fireball kept expanding and climbing at over 200 miles per hour,
reaching an altitude of about 2 miles. The boiling mass 20 miles away
turned into a mixture of white and gray vapor and continued its climb
until it reached somewhere about 100,000 feet.

Meanwhile, the lagoon water had receded like a curtain being pulled
back, and the sea bottom slowly appeared. Shark netting that usually
protected swimmers lay on the bottom.

Finally, the water stopped receding and appeared to form a wall, like
pictures of Moses parting the sea. The wall seemed to remain motionless
before finally roaring back.

The water receded for a second time, then repeatedly in smaller and
smaller waves and finally as minuscule oscillations across the lagoon
surface that lasted all day.
/""

https://www.youtube.com/watch?v=NV9Z6cGER80

Note how the paint peels off first, due to the heat wave -- this
is radiation heat, hence travels very fast. The shock wave (air)
arrives a few seconds later, allowing to estimate that the bus
was somewhat less than a mile from the bomb.