Alternative decoder 

my $data = "\x58\x02\x77\x21\x1F";

my $rain_clicks = Int(substr($data, 0, 2));
my $rain_rate   = Int(substr($data, 2, 2));
my $uv_index    = ord(substr($data, 4, 1));

• Could be written as:

my($rain_clicks, $rain_rate, $uv_index) = unpack('SSC', $data);