How can I create an arrow with color gradient scaled by month using geom_curve?

I wish to show a curved arrow whose color gradient changes according to month, superimposed on a map of the eastern seaboard

require(sf); require(maps); require(ggplot2)
usmap <- st_as_sf(map("state", plot = F, fill = TRUE))  #  sf functions & methods that operate on spatial data are prefixed by st_ (spatial type)
seaboard <- c('alabama', 'connecticut', 'georgia', 'maryland', 'mississippi', 'new jersey','new york', 'pennsylvania', 'south carolina', 'florida', 'north carolina', 'delaware','rhode island',
    'massachusetts', 'virginia')
monseq <- c('September','October','November','December')

ggplot(data = usmap[usmap$ID %in% seaboard,]) +
    geom_sf() +                                     # grey default background for states
    theme_bw() +                                    # black grid lines on white background
    geom_curve(
        aes(x = -75, y = 42.5, xend = -85, yend = 30.5, size=3),
            curvature = -0.2, 
            lineend = "round",
            arrow = arrow(length = unit(0.3, "cm"))
    ) +
    scale_colour_gradient(low = "red", high = "blue")

This as far as I've gotten. I also wish to add a circle composed of three black nose-to-tail arrows pointing in a clockwise direction, located above the head of the arrow.