なあ

なあ
particle
expresses emotion or emphasis (sentence-final)
informalgrammatical
1. you know; I tell you; how ...! (emotion, reflection, or emphasis)
A casual sentence-final particle that adds feeling to a statement — admiration, longing, mild emphasis, or a wish for the listener's agreement. A lengthened, more emotive form of な.
いい天気(てんき)だなあ。
What lovely weather!
I wish summer vacation would hurry up and come.
Those days really were fun, weren't they.
If only it were a bit cheaper, I'd buy it, you know.

Register: Casual. Common in male speech and in relaxed conversation; it can sound slightly rough, so it is avoided in polite or formal situations.

Nuance: Adds an emotional coloring such as:

Usage: When used to seek the listener's agreement, it overlaps with but feels more inward and reflective. なあ can also begin an utterance as a soft call for attention: なあ、()てる? (Hey, are you listening?).