Summer is over, and the speaker seems to be taking its last moments in rather than mourning them. The image of fitting oneself to the white sand "like a lover" is tender and physical. The speaker presses close to the ground, as if holding on to the warmth and the beach for a little longer. The title, "Miss September," adds a playful note. It can suggest missing the month, and perhaps also the idea of a pin-up, which fits the sensual comparison.
In the second stanza, the longing shifts from the beach to indoor life: "a multitude of books and evenings." The speaker is already looking forward to autumn, to quiet reading and the arrival of "amorous rains." Rain is described like a lover too, so the two stanzas echo each other. The mood is wistful but calm and affectionate. Nothing is lost for good here, because one kind of pleasure is simply giving way to another.