The central image of the first section of this poem is death. The section talks about ghosts and graves and corpses and pestilence. The wind is like death, sweeping away all life. To me, at least, this evokes negative feelings -- disgust, and a bit of fear.
The second section or stanza is more supernatural. It talks about angels and maenads (from Greek mythology). This is less gruesome but more wild (that was the main characteristic of maenads). It feels uncontrolled to me.
In the third section, the theme is of things being awakened. It seems much more peaceful until the last couple of lines, which are much more fearful.
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 as the "breath of autumn's being" 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.
In the first canto the image of the west wind is that of both a 'destroyer' and a '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.
The central image of canto 2 is that of the "fierce Maenad" which conveys the fury and the violence of the west wind.
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.
The central image in canto 3 is the "voice" of the west wind which announces to the underwater vegetation in the depths of the ocean that it is time for them to "despoil themselves."