Arvi Laanemets wrote...
Several ways exist:

Indeed.

1. Convert the month name to date, and calculate month number from it - like
=MONTH(DATEVALUE("01." & A1 & "." & YEAR(TODAY())))
(NB! use valid for your regional settings date string format)
....

As long as the OP's language is English and the month names are spelled
correctly, both

=MONTH("1 "&A1)

and

=MONTH(A1&" 1")

return the month number for A1 no matter what the system date formats
may be.