Giving premonition; serving to warn or notify beforehand.

adjective. Giving previous warning or notice.

adjective. Serving as a warning.

adjective. warning of future misfortune

"Scientists have long known about this so-called premonitory phase, which occurs well before the better-known aura, the flashing lights and wavy lines that about 30% of migraine sufferers see shortly before the headache begins."

prophetic  prophetical  

agonal  aguish  animalistic  anticipatory  atavistic  

augural  foreboding  forerunning  foreshadowing  foreshowing