PHP form only returning empty array - php

Question

I am working on a code segment that is a messaging function next to a list of names. On the page there is an envelope and when you click it a pop-up window appears with a text area inside of it. I would like to be able to fill that textarea with characters and send it as a message using my already functioning sendMessage function. I know my sendMessage function works and I've isolated the issue to the return given by the submit button. How do I get my submit button to POST the textarea to the page (keep in mind there are 2+ forms on this page). The code looks like this:
if (empty($_POST) === false) {
print_r($_POST);
$blah = $_POST;
echo "<script>window.top.location='asd.$blah'</script>";
}
if (empty($_POST['Send']) === false) {
echo "<script>window.top.location='../hidden/PNMasdd.php?gpa=$var1&year=$var2&major=$var3&sport=$var4'</script>";
echo 'YOU ARE IN THE SENDING MESSAGE FIELD';
if( empty ($_POST['message_full']))
{
$errors[] = 'All fields must be filled in!';
//print_r($errors);
}
if(empty($_POST) === false && empty($errors) === true)
{
$receiver_id = $temp_user['id'];
$sender_id = $user_data['id'];
$type = 0;
if(empty($is_Convo))
{
$is_Convo = 0;
}
$blahVar = $user_data['id'] . ',';
$message = str_replace("\r\n", "<br>", $_POST['message_full']);
$message_data = array(
'sender_id' => $user_data['id'],
'receiver_id' => $receiver_id,
'message_full' => $message,
'is_opened' => $blahVar,
'isConvo' => $is_Convo,
'type' => $type
);
//Put data limit code here
send_message($message_data);
$my_exten = "Messages/messages.php";
$noti_data = array(
'id_receive' => $receiver_id,
'id_sent' => $user_data['id'],
'type' => 1,
'exten' => $my_exten
);
notify($noti_data);
echo '<center>';
echo '<div class="alert alert-info">
<strong>It sent!</strong> You have sent a message successfully!
</div>
';
echo '</center>';
}
else{
echo output_errors($errors);
}
}
?>
<form id="wow" name="wow" action="" method="POST">
<div class="row">
</div>
<div class="row">
<div class="form-group">
<div class="col-md-12">
<center>
<textarea maxlength="100000" data-msg-required="Please enter your message." rows="10" cols="100%" class="form-control" name="message_full" id="message_full"></textarea>
</center>
</div>
</div>
</div>
</form>
</div>
<div class="modal-footer">
<table width=90%><td width=45%><button type="button" class="btn btn-default" data-dismiss="modal">Cancel</button></td><td width=45%>
<button type="submit" value="Send Message" name="Send" onclick="document.getElementById('wow').submit()" class="btn btn-primary">Send</button>

Answer 1

As pointed out in the comments, the buttons need to be inside your form.
Your setup is a bit odd for my taste, but try this out.. it will mostlikely need some tweaks and i'm not sure about the cancel button..
<form id="wow" name="wow" action="" method="post" >
<div class="form-group required">
<div class="col-md-12">
<textarea name="message_full" id="message_full" rows="10" cols="100%" class="form-control" maxlength="10000" placeholder="Please enter your message." autocomplete="off"></textarea>
</div>
</div>
<div class="buttons"> <!-- add css for this or change the class to yours.. -->
<input class="btn btn-default" data-dismiss="modal" value="Cancel" />
<input class="btn btn-primary" type="submit" value="Send Message" />
</div>
</form>

Answer 2

As #Barmar just said, you don't have any field named 'Send'. You should change:
if (empty($_POST['Send']) === false)
to:
if (empty($_POST['message_full']) === false)
(Edit)
Only the fields inside your form will get to $_POST superglobal, the submit button will not get there