These are draft notes

The painting of the Rising Squall

The painting of 'The Rising Squall' may have been Turner's idea or it may have been a definite commission from Nixon. Either way, the picture was sold or given to Nixon.
Either Turner, Nixon or both would have been influenced by 'Rochester Castle with Fishermen Drawing Boats Ashore In A Gale of Wind' and it is possible that Nixon had seen the already completed watercolor-drawing 'View on the river Avon, near St. Vincent's rock, Bristol' and commissioned a stormy piece based on St. Vincent's Rock.
In the Bristol and Malmesbury Sketchbook there was D00074 but there was no 'feature' on it that could adequately represent 'St. Vincent's Rock'. Research pages by Tate Gallery show D00389 as the precursor for 'The Rising Squall'

At this point the following sketches and watercolour drawings come into play:

comparatives

cf:Fantasy Landscape -> Ibbetson page35 and 262