Its companion piece is called 'Shade and Darkness — the Evening of the Deluge' and is also in the Tate. Both were painted late in Turner's life (around 1842/3) and first exhibited in 1843.
They failed to sell and formed part of the Turner Bequest which was left to the nation in 1856 and is located at Tate Britain. They are not always on display, but you can see them until April 2010 in the Clore Gallery at Tate Britain, where they form part of a display called "Colour and Line - Turner's Experiments". One object in this exhibition is Turner's own, heavily annotated copy of Goethe's 'Theory of Colours', translated by Charles Eastlake and published in 1840. Since the book is on display I wasn't able to inspect it, but the very helpful archivist of the Clore Gallery dug out the photographs of each individual page for me. The book does not form part of the Turner Bequest; it is in a private collection and on temporary loan.
From the Tate online collection: "Turner opposes cool and warm colours, and their contrasting emotional associations, as described by Goethe in his 'Farbenlehre' (Theory of Colours). Turner has chosen the biblical Deluge as the vehicle for these ideas, returning to the Historical Sublime he had mastered in some of his earliest exhibition pictures. Originally painted and framed as octagons, this pair carries two of Turner's last and most inspired statements of the natural vortex, while the allusion to Goethe adds a gloss of recent science and theory to a lifetime's preoccupation with elemental forces
Here is an interesting interpretation of the deluge painting by the artist Paul Pfeiffer:
More on the pair here:
"Idyllic, dream-like landscape, often of Venice, represented one side of Turner's late style. The other was the increasingly direct expression of the destructiveness of nature, apparent particularly in some of his seapieces. The force of wind and water was conveyed both by his open, vigorous brushwork and, in many cases, by a revolving vortex-like composition. In the unexhibited pictures these forces were treated in their own right, but in most of his exhibited works (the distinction lessened in his later years) they were expressed through appropriate subjects such as the Deluge or the Angel of the Apocalypse. In some of these pictures Turner used a colour symbolism, partly deriving from Goethe's theories, as in the pair of pictures 'Shade and Darkness - The Evenening of the Deluge' and 'Light and Colour - the Morning after the Deluge', exhibited in 1843 with a specific reference to Goethe. These pictures are examples of Turner's experiments with square, octagonal or circular formats in which the vortex composition found its most compact and energetic expression." From "Tate Gallery - An Illlustrated Companion", 1990, by Simon Wilson
Here is another example of one of Turner's vortex pictures, 'The Angel Standing in the Sun', also part of the Turner Bequest, first exhibited 1846: