All 4 Uses of

however
in
Flipped, by Wendelin Van Draanen

My father, however, understood that you can't refuse to do your teacher's assignment, and he promised to help.
p. 67.8 *

however = a word used to connect contrasting ideas as when using though, in spite of that, in contrast, nevertheless, etc.

How he knew about incubators, however, was revealed to me while he was drilling a one-inch hole in an old scrap of Plexiglas.
p. 68.0

The tornado, however, was still going strong when I skidded to a halt in our driveway.
p. 111.9

Definitions:

(1) (however as in: However, complications may...)
though (or another expression that connects contrasting ideas)

(Based on idea 1 we might not expect idea 2, but this is a way of saying that even though idea 1 exists, we still have idea 2. Synonyms include in spite of that, despite that, nevertheless, nonetheless, on the other hand, in contrastand but.)
(2) (however as in: However much she tried...)
to whatever degree (regardless of how much; or whatever unspecified amount)
(3) (however as in: However you do it, get it done!)
in whatever way
(4) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely (and arguably incorrectly), however can be used to intensify the word how, as when one says "However did you find her?" Grammarians would suggest using two words for that usage: "How ever did you find her?"