my %h1 = (
    'Jan' => 'a',
    'Feb' => 'b',
    ...
    'Dec' => 'l',
);

my %h2 = (
    'a' => 'Jan',
    'b' => 'Feb',
    ...
    'l' => 'Dec',
);

my @sorted_dates =
    grep { s/^(.)(\d\d)/$e{$1} . ' ' . sprintf("%d",$2)/e }
    sort
    grep { s/^(.{3}) (\d\d?)/$d{$1} . sprintf("%02d",$2)/e; }
    @dates;