IPA: //saʊθˈwɛrdz//
KK: /sɑʊθˈwɛtərdz/
In the direction that is between south and west.
The storm is moving southwestwards, away from the coast.
Southwestwards is formed from "south" (from Old English *sūþ*, meaning the direction toward the south) and "west" (from Old English *west*, meaning the direction toward the west) combined with "-wards" (meaning in the direction of). The word describes a direction that is toward the southwest.
Think of heading in the direction of 'south' and 'west' together, and remember that 'southwestwards' means moving toward that combined direction.