The numbers show the temp of the upper surface of the tyre (not the contact patch). Thus if the wheel rotates it will show different temperatures each time a new section comes into play. But you should have pretty even numbers unless you're locking your brakes - are there bright red 'flashes' as you drive?
Try to lock your wheels less. The 'refresh' rate of the F9 screen is directly proportional to your speed, so the flashing occurs because once every x frames the hotspot on your tyres is as the top of the wheel and briefly displays.