The script bellow works on the latest MacOS and you can use it to open your Markdown editor and start writting:
set theResponse to display dialog "Post Title:" default answer "" buttons {"Cancel", "New Post"} default button 2 with title "New Post"
set title to (text returned of theResponse)
set slug to do shell script "echo `date '+%F'`'-" & (title & "' | tr '[:upper:]' '[:lower:]' | sed 's/ /-/g'")
set workingDir to "/Users/CHANGETHIS"
set postPath to "/content"
set postSlug to "/post/" & slug & "/index.md"
set postPathSlug to workingDir & postPath & postSlug
set shellScript to "export TITLE='" & title & "' ; cd " & workingDir & "; /usr/local/bin/hugo new " & postSlug & "; open " & postPathSlug
do shell script shellScript