I'd like to stretch below tabular to a width of 15 cm width which is wider than the original table.
\documentclass{article}
\usepackage[landscape]{geometry}
\begin{document}
\begin{tabular}{|l|r|r|r|r|r|r|r|r|r|r|r|r|}
\hline
& Jan & Feb & Mar & Apr & May & Jun & Jul & Aug & Sep & Oct & Nov & Dec\\
\hline
2016 & 2.5 & 1.3 & & & & & & & & & &\\
\hline
2015 & & 0.6 & 5.2 & 8.5 & 0.3 & 1.4 & 0.5 & 3.9 & 7.1 & 2.4 & 2.3 & -999.9\\
\hline
\end{tabular}
\end{document}
I use the tabu environment as shown below. While this produces a table with desired width, long cells now contain a line break (see cell for Dec 2015).
\documentclass{article}
\usepackage{tabu}
\usepackage[landscape]{geometry}
\begin{document}
\begin{tabu} to 15cm {|X[l]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|X[r]|}
\hline
& Jan & Feb & Mar & Apr & May & Jun & Jul & Aug & Sep & Oct & Nov & Dec\\
\hline
2016 & 2.5 & 1.3 & & & & & & & & & &\\
\hline
2015 & & 0.6 & 5.2 & 8.5 & 0.3 & 1.4 & 0.5 & 3.9 & 7.1 & 2.4 & 2.3 & -999.9\\
\hline
\end{tabu}
\end{document}
How can I stretch the table to fill the available width without breaking cell content in two lines?