The loss of a parent is hard, especially if they were important in your life, helping shape you as a child so you would grow into a healthy adult. It is clear he took pride in his work!
Your vivid description of the way you are experiencing 'grief' is almost too real. The word 'howling' is so much more than 'crying' it shows the level of pain - more verging on a mental breakdown. This external 'lament' then internalises to a 'heave' within. Both the internal and external symptoms happen like in an instant, without warning 'Bang' and in the middle of the 'mundane' it hits you hard.
I remember this feeling when I lost my sister. I would be going about my normal business and Pow, I would feel crippled and tears would spring to my eyes.
These moment of 'gut' punching pain will continue to occur and should be embraced. They remind us that our loved ones are never truly gone, they are with us always, mingled in the everyday, there likes, dislikes, aromas and so much more.
I am sure your 'Acha' is hugging you from within, holding your heart, just like you held his and still do. ((hugs))