My dictionaries and references define, and I've always thought of, one of the functions of the word whatever as a "relative determiner."
In a sentence like, "I will help you in whatever way is possible," inserting the relative pronoun "that" between "way" and "is", or replacing "whatever" with "the" - a pure, non-relative determiner - (I reckon) renders it ungrammatical:
*I will help you in whatever way that is possible.
*I will help you in the way is possible.
However, I do often encounter utterances like the first one above, such as:
My hope and intent is to contribute in whatever way that I can.
I wish to be of service to the local communities in whatever way that is possible.
where "that" is used, and thus "whatever" can be replaced by "the" without making the sentences ungrammatical (if they are grammatical to begin with):
My hope and intent is to contribute in the way that I can.
I wish to be of service to the local communities in the way that is possible.
Is this usage of "that" with "whatever" wrong, though colloquial?