The usual definition of eccentricity of a vertex $v$ in an **unweighted** graph $G$ is the maximum over all distance from $v$ to vertices $w\in G$. You can use literally exactly the same definition for a weighted graph.
More explicitly, for a connected undirected weighted graph $G=(V,E,w)$ where $w:E\to \mathbb R^{\geq 0}$ is a weight function, define the distance between vertices $v,w$ to be $$d_G(v,w)=\min_P \sum_{e\in P}w(e) $$ where the minimum is over all paths $P$ connecting $v$ and $w$.
Now define the eccentricity of a vertex $v$ as $$e_G(v)=\max_w d_G(v,w).$$
Not sure how widespread the use of this definition is but it seems to be a pretty natural generalization.