IPA: //ˌsaʊθˈiːstwərdz//
KK: /sautˈhwestwərdz/
In the direction that is between south and east.
The storm is moving southeastwards, bringing heavy rain to the area.
Southeastwards → It is formed from "south" (from Old English *sūþ*, meaning the direction towards the south) and "east" (from Old English *ēast*, meaning the direction towards the east) combined with "-wards" (meaning in the direction of). The word "southeastwards" means in the direction towards the southeast.
Think of heading towards the 'south' and 'east' — that's why 'southeastwards' means moving in that direction.