Heres how I fixed it:
I created an empty div on the page with the id of error-dialog
and gave it css display: none;
.
Then I changed my code to this:
$('#error-dialog').html('The following are required:<br /><br /><i>'+$errors+'</i><br />Please complete these in order to continue.');
$('#error-dialog').dialog({
modal: true,
title: "Error",
buttons: {
Ok: function () {
$(this).dialog("close");
}
}
});
Now it is populating the dialog with content before display it, therefore allowing it to center itself properly.