high tide vs the flag is up

high tide

noun
  • Synonym of menstruation 

  • The natural tide at its highest level for a particular tidal cycle at a certain place. 

  • climax, culminating point or phase 

  • The time of day when the sea has risen to its highest level. 

the flag is up

How often have the words high tide and the flag is up occurred in a corpus of books? (source: Google Ngram Viewer )