Is it possible for topical preaching to be expository?

Yes, answers Timothy S. Warren, in chapter 112 of The Art and Craft of Biblical Preaching (eds Robinson & Larson).

Topical preaching is popular.  Hearers appreciate preaching that addresses their immediate interests and concerns.

Topical preaching is biblical.  With the exception of Ezra (in Nehemiah 8) and our Lord himself (in Luke 4), no other preacher in the Bible began with a text.  Peter (in Acts 2) and Paul (in Acts 13) wove multiple texts into a single message.

Textual expository preaching finds its message in a single verse or sentence.

Consecutive expository preaching finds its message in a literary unit, while moving through a book of the Bible (or substantial part of it).

Topical expository preaching ‘finds its message in two or more different texts or units in their individual contexts that share a common subject.’

In common with all expository preaching, topical expository preaching proceeds through four movements:

1. Exegetical.  A historical/contextual, grammatical/syntactical, normal/literal, literary/rhetorical hermeneutic is used to distill the essential meaning of the passage.
2. Theological.  This seeks to move from the particulars of the text’s essential meaning to its timeless truth.  The progress of revelation (culminating in Christ) must be taken into account, and also the controls imposed by systematic theology.
3. Homiletical.  The theological proposition is interrogated with the audience in mind: What will this mean to them?  Will they believe it?  What difference will it make in their lives?
4. Applicatory.  ‘I will not have completed the full expositional process until I and my listeners follow the demands of the text in our own thinking, feeling, and doing.’