How do I serialize data in a button's surrounding form?

I have a simple form:

<div id="notify-alert"></div>
<form method="post">
<input type="hidden" name="memberID" value="5">
<input type="hidden" name="requestID" value="23">
<input type="button" name="submitNotify" value="Notify" onclick="SubmitNotification();">
</form>

the SubmitNotification function is as follows:

function SubmitNotification(){
	//these next four lines were to check what was going on
	var thisData = $(this).closest('form').serialize(); 
	console.log('begin');
	console.log(thisData);
	console.log('end');
	$.ajax({
		type: "POST",
		url: "ajax-notify.cfm",
		data: $(this).closest('form').serialize(),
		dataType: "text",
		success: function(data, status) {
			$('#notify-alert').html(data);
		},
		error: function(data, status) {
			$('#notify-alert').html(data);
		}
	});
};

$(this).closest('form').serialize(); is just returning an empty string. I've found several questions about how to serialize the surrounding form of a button and this appears to be to the correct way... where is this going awry? (I've also tried $(this).parent('form') with the same issue. Incidentally, I'm not using an ID for this because there are multiple forms on the page created by a loop.) Thanks!