The rain started in the early hours, with 13.6mm falling at Guernsey Airport between 2.30 and 9.30am, according to a Tweet from the Guernsey Met Office, which warned that there was more to come.
And more there was, with 27.2mm having fallen in total by the time the Met Office tweeted again at 12.45, once more warning that it was not over yet.
By the end of the day, the island had seen a total of 52mm.
While high, this was still below the wettest August day on record, however. That was in 1973 when rainfall of 55.8mm was recorded.
But a Met Office spokesman said that the day was likely to be among the five wettest for the month.
Summerfield Road in the Vale was closed and Iceland, on its corner with Vale Avenue, closed temporarily to avoid flooding, with staff putting sandbags out to keep the water at bay.
A spokesman for franchise holders Sandpiper said that the company would be contacting the authorities to find out what more could be done to stop the build-up of water in the area during periods of heavy rain.
