What does %base_stat contain before entering the first iteration of the loop? If %base_stat contains nothing, your first iteration of the loop will be performing operations on @temp_array when it too contains nothing. Perl is warning you that you're making a mistake. See the following snippet that should clarify for you.

use 5.012.02;
use strict;
use warnings;

my %basestat;
my @temparray;
my $basecount = 1;

@temparray = $basestat{$basecount};
say "\$temparray[0] is ", defined( $temparray[0] ) ? "defined." : "und
+efined.";
say "\@temparray has ", scalar(@temparray), " elements.";
say "\$temparray[0] = $temparray[0]";
say "\@temparray = @temparray";
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And the output:

Use of uninitialized value $temparray[0] in concatenation (.) or strin
+g at test.pl line 14.
Use of uninitialized value $temparray[0] in join or string at test.pl 
+line 15.
$temparray[0] is undefined.
@temparray has 1 elements.
$temparray[0] = 
@temparray =
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This snippet more or less constructs the state your code experiences on the first iteration of the loop. I'm surprised you're not getting a warning two lines later in the script too, where you wrap @temparray in quotes. On your subsequent loop iterations %basestat and @temparray contain values, and so you no longer are attempting to use the values of uninitialized variables, so your warnings go away.

I think if you dig a little deeper you'll find that there's a better way to do what you're trying to do.