This may be really easy but I can\'t find a PHP function to do this...
OK so
$dow_numeric = date(\'w\');
gives the numeric day of t
If you need locale support you can use a bit improved function of Hamishs answer:
Example using german weekdays:
setlocale(LC_TIME, 'de_DE');
$dow_numeric = 3;
$dow_text = strftime('%A', strtotime("Sunday +{$dow_numeric} days"));
http://php.net/strftime
If $dow_numeric start on 0 (0 = Monday) you can just change Sunday to Monday or
add $dow_numeric += 1