It was worst of all in the summer...

The situation is not being compared with other situations. It is compared with itself. That's why the definite article cannot be used. There is an alternative, though: The situation was [at its] worst during the summer as the power outage was rampant.

Other examples:
He is [at his] happiest in the mornings.
The lake is [at its] deepest here.

Thanks for the reply, Cool Breeze.

So, the use of the definite article will be wrong in all these examples?

The situation was the worst during the summer as the power outage was rampant.
He is the happiest in the mornings.
The lake is the deepest here.

Tom

Right you are! Wrong it is!

CB

Mr. TomCould you please tell me why there is no article before "worst"? Also, is it some kind of grammar rule?It was worst of all during the summer as the power outage was rampant.

I don't think I can explain it. "the worst of all" seems fine to me. I haven't really thought about it, but it seems to me that "the" is usually optional in these constructions.

Mr. TomThe situation was the worst during the summer as the power outage was rampant.He is the happiest in the mornings.The lake is the deepest here.

For some reason, these don't bother me as much as they do CB, though I prefer them without "the".

CJ

Mr. TomThanks for the reply, Cool Breeze.So, the use of the definite article will be wrong in all these examples?The situation was the worst during the summer as the power outage was rampant.He is the happiest in the mornings.The lake is the deepest here.Tom

Reading those, I'm beginning to think you have take each case as it comes.

The last one change

It occurs to me that there is one "rule", or at least I think it's a rule with very few, if any, exceptions, and that is that you have to use "the" with a superlative if there is an in-phrase (or equivalent) that tells the group from which the comparison is drawn.

(She is) the richest in the room. (person)
(It is) the most beautiful in the world. (gem)
(It is) the longest

Thanks a lot for the valuable input.

The in-phrase does not work with one of the sentences Cool Breeze wrote, CJ.

He is happiest in the mornings.
[Is it because he is being compared to himself?]

Or am I missing something?

Tom

Mr. TomThe in-phrase does not work with one of the sentences Cool Breeze wrote, CJ.He is happiest in the mornings. [Is it because he is being compared to himself?]Or am I missing something?

Yes, you're missing the fact that the universe of comparison is not mornings! It makes no sense to think that the sentence is selecting "he" (him) from among all mornings