 Cloud often forms inland , especially near hills , and reduce the amount of sunshine that reaches the park . The average annual sunshine is about 1 @,@ 600 hours . Rainfall tends to be associated with Atlantic depressions or with convection . In summer , convection , caused by the sun heating the land surface more than the sea , sometimes forms rain clouds and at that time of year a large proportion of the rainfall comes from showers and thunderstorms . Annual precipitation varies from 800 mm ( 31 in ) in the east of the park to over 2 @,@ 000 mm ( 79 in ) at The Chains . However , in the 24 hours of 16 August 1952 , more than 225 mm ( 8 @.@ 9 in ) of rain fell at The Chains . This rainfall , which followed an exceptionally wet summer , led to disastrous flooding in Lynmouth with 34 dead and extensive damage to the small town . 
