Shelley composed the "Ode to the West Wind" while in Florence, Italy in the year 1819. It was published in the year 1820. The gist of the poem is that Shelley considers himself as a poet prophet campaigning for reform and revolution using the "wild west wind" to destroy everything that is old and defunct and plant new and progressive, liberal and democratic ideals in its stead. The poem describes a storm arising in the autumn season in the Mediterranean Sea and being driven towards the land by 'the west wind.'
In Canto 1, Shelley addresses the west wind directly and the sight of it driving away all the fallen leaves is compared to a magician or an enchanter driving away all the evil spirits. At the same time it carries with it the fallen seeds to deposit them in a different place where they will blossom in the spring season after being safely preserved during the cold winter season. The west wind is thus both 'destroyer' and 'preserver.'
In Canto 2 Shelley vividly describes the meteorological process of the gathering storm in the distant horizon of the Mediterranean Sea.
In the first stanza Shelley compares the storm clouds which are being formed at the horizon ("tangled boughs of Heaven and Ocean") and being driven inland by the west wind to decaying leaves shed by the trees during autumn.
In the next two stanzas, the storm clouds are compared to "angels" which carry the rain inland. They announce their arrival by fiery flashes of dazzling lightning which reach up into the sky from the ocean at the horizon. The flashes of lightning are compared to the bright hair of the maenad (the maenad is a frenzied spirit which attends on the Greek God Dionysus.
In Canto 3 Shelley describes the action of the west wind on the Mediterranean Sea and on the Atlantic Ocean. The west wind announces to the Mediterranean Sea that summer is over and autumn has arrived. The clear view on a bright summer day of the under water palaces and towers in Baiae's Bay off the coast of Naples near the island made up of volcanic rock is disturbed by the west wind which blows across it. Similarly the west wind creates deep valleys as it blows across the level Atlantic Ocean and reminds the underwater vegetation deep below that it is autumn and that they too must disintegrate like the vegetation on the earth above.
Canto 4 is an earnest plea by Shelley to the west wind to infuse him with its raw power and liberate him from the bout of depression which has temporarily overwhelmed him - most probably caused by the death of his son William in 1819. Shelley tells the west wind that when he was a boy he was also as "uncontrollable" as the west wind is now, and he would have easily matched the west wind in its speed. But now, he is depressed and weighed down by the cares and anxieties of life and prays to the west wind to liberate him. He pleads with the west wind that just like how it lifts up the leaves on the earth and the clouds on the sky and the waves on the sea it should free him also from the "thorns of life" on which he has fallen.
In Canto 5, Shelley the poet directly and explicitly asks the west wind to make him an instrument and tool of political and moral change: "make me thy lyre" and "drive my dead thoughts over the universe." The poem ends optimistically with Shelley echoing the popular saying "if Winter comes can Spring be far behind?"