R/get_met_forecast_nam.R

In rich-iannone/SplitR: Use the HYSPLIT model from inside R

#' Read NAM meteorological forecast data files
#'
#' This function downloads NAM meteorology forecast data files from the NOAA FTP
#' server and saves them to a specified folder.
#' 
#' @inheritParams get_met_gdas1
#' 
#' @export
get_met_forecast_nam <- function(path_met_files) {
  
  # Establish which forecast dirs are currently 
  # available on the server
  forecast_dirs <-
    grep(
      "^[0-9].*$",
      unlist(
        strsplit(
          RCurl::getURL(
            "ftp://arlftp.arlhq.noaa.gov/forecast/",
            dirlistonly = TRUE),
          "\n")
      ), 
      value = TRUE
    )
  
  # Get today's date and write in format equivalent
  # to FTP directories 
  today <- gsub("-", "", Sys.Date())
  
  # Download today's `namf` file
  # -- CONUS, 12 km, 3 hrly, pressure levels, 48 h forecast
  
  if (today %in% forecast_dirs) {
    
    downloader::download(
      url = paste0(
        "ftp://arlftp.arlhq.noaa.gov/forecast/",
        today, "/hysplit.t00z.namf"),
      destfile = paste0(path_met_files, paste0(today, ".t00z.namf")),
      method = "auto",
      quiet = FALSE,
      mode = "w",
      cacheOK = TRUE
    )
  } 
}