Here's why:
* Predicate: The predicate is the part of the sentence that tells us something about the subject.
* Subject: The subject of this sentence is "storm trackers".
* Verb: The verb "are" connects the subject to the rest of the predicate.
* Predicate Nominative: "reliable information gatherers" is a noun phrase that renames the subject and is the part of the predicate that provides more information about the subject.
Therefore, "are" is the predicate word because it is the verb that connects the subject to the predicate nominative.