I have tested this on the OS X El Capitan GM and a few of the developer seeds (I can't remember which ones); it probably doesn't work on older versions.
To go in the other direction, see Steven Frank's notes-import script.
--
-- notes-export.scpt
-- Alex Chan <[email protected]>
--
-- Export all the notes from Notes.app into a folder as HTML text.
-- A very basic backup script.
--
-- Usage:
-- * Open this file in Script Editor
-- * Run
-- * Select a folder to export files to
--
-- Output:
-- * A collection of (Latin-1 encoded) HTML files
-- * A list of attachment names for each note.
--
-- Known issues:
-- * Only the names of attachments are exported, not the files
-- themselves. (Look for the files in
-- ~Library/Group Containers/group.com.apple.notes/Media).
-- * Some attachment types (e.g. app links) show up as "Missing value"
-- * Some formatting is lost.
-- * A note with the same title as a previously exported note will be
-- overwritten.
-- * It will exported notes in the "Recently Deleted" folder which
-- haven't been purged from disk yet.
--