Not safe to even consider going out!*
Scroll the time selection on the link below ( move the rectangle box at the bottom) to 12:30 and see what’s coming!
https://www.metoffice.gov.uk/weather/maps-and-charts/rainfall-radar-forecast-map* …….or probably even being under the trees in the boat park.
Is it worth checking covers and boats on moorings earlier in the morning???