The downpour started just after 4.30am, according to Guernsey Met Office.
'It didn't let up – it was either moderate or heavy – until just after noon,' a spokesman said.
'In that time there was 25mm of rain.
'That's almost as much rain as the entire month of December, when there was 27.5mm.'
The 30-year average for March is 67mm.
The wet weather resulted in a number of roads being flooded.
