The story
From be- + storm. Compare Old English bestyrman (“to agitate”). Cognate with Saterland Frisian bestoarmje (“to storm; besiege”), West Frisian bestoarmje (“to storm; besiege”), Dutch bestormen (“to storm, assault, rush, attack”), German bestürmen (“to storm, besiege, bombard, inundate”), Swedish bestorma (“to besiege, attack, assail”).
Etymology from Wiktionary, CC BY-SA 4.0.