Facet_grid w/ Dates Oct thru Sept - r

Question

I'm working with a dataset that is typically analyzed using start and end dates that differ from a typical calendar year (water years run October 1 to Sept 30). I have no problem plotting the data in ggplot but as soon as I try to use facet_grid to break up the years, the data get misrepresented.
#Create data set
WY18to21 <- as.data.frame(seq(as.Date("2017-10-01"), as.Date("2021-09-30"), "days"))
names(WY18to21) <- c("Date")
WY18to21$Year <- year(WY18to21$Date)
WY18to21$Temp <- c(rep(seq(1,25, by=0.1), times=6), 1:15)
#Create "yearless" date for facet plot
WY18to21$Date_md <- WY18to21$Date
year(WY18to21$Date_md) <- 2000
#Set Water Year (WY)
WY18to21$WY <- "NA"
WY18to21$WY <- ifelse(WY18to21$Date >= as.Date("2017-10-01") &
WY18to21$Date <= as.Date("2018-09-30"), "WY18",WY18to21$WY)
WY18to21$WY <- ifelse(WY18to21$Date >= as.Date("2018-10-01") &
WY18to21$Date <= as.Date("2019-09-30"), "WY19",WY18to21$WY)
WY18to21$WY <- ifelse(WY18to21$Date >= as.Date("2019-10-01") &
WY18to21$Date <= as.Date("2020-09-30"), "WY20",WY18to21$WY)
WY18to21$WY <- ifelse(WY18to21$Date >= as.Date("2020-10-01") &
WY18to21$Date <= as.Date("2021-09-30"), "WY21",WY18to21$WY)
#Plot - regular ggplot
x <- ggplot(WY18to21) +
geom_line(aes(Date, Temp)) +
xlab("") + ylab("[°C]") +
ylim(0,26) +
theme_bw() +
scale_x_date(date_labels = "%b")
x
This looks okay, but I find the aesthetic of facet plots easier to interpret
x <- ggplot(WY18to21) +
geom_line(aes(Date_md, Temp)) +
xlab("") + ylab("[°C]") +
ylim(0,26) +
theme_bw() +
scale_x_date(date_labels = "%b")
x_facet <- x + facet_grid(. ~ WY)
x_facet
It looks like the facet_grid function first splits the data by water year (WY) and then orders the data by the "yearless" date. In practice this means the beginning of the next water year gets moved to the beginning of the current water year.
What I need to do is figure out either:
(a) how do I use facet_grid with dates without removing the year OR
(b) how do I redefine the order dates are plotted so that the year begins on October 1.
Attempts at problem solving: I think the solution has something to do with the mutate function but I have yet to successfully figure that out. I also tried searching under "fiscal year" since often they are also different than calendar years. But no luck. Thanks for the help!