Heavy rain warning was first introduced in April 1967 together with thunderstorm warning by the Royal Observatory of Hong Kong as a result of the three rainstorms in 1966 which claimed 86 lives. The heavy rain warning was issued when an hourly rainfall of more than 50 mm (2 inches before metrication) was expected in six hours. Both heavy rain and thunderstorm warnings were issued to the public through press release, radio broadcast and telephone calling service to subscribers. In 1983, the heavy rain warning was replaced by flood and landslip warnings.