The phrase "brewing storm" means that a difficult or dangerous situation is starting to build up, similar to how a storm begins to form and gather strength before it strikes. Full definition
The FBI said Harris swindled local and federal agencies out of «thousands of dollars... (and) at a time when many residents in her district were dealing with the horrific aftermath of Hurricane Sandy, Harris was busy brewing a storm of her own, one that resulted in her receiving significant payouts by the very federal agency charged with helping those truly in need.» (timesunion.com)
«At a time when many residents in her district were dealing with the horrific aftermath of Hurricane Sandy, Harris was busy brewing a storm of her own, one that resulted in her receiving significant payouts by the very federal agency charged with helping those truly in need,» William Sweeney, the FBI's assistant director in charge in New York, said in a statement. (patch.com)
Or are there undeterminable factors constantly at work, likes brewing storm that may or may not get enough moisture to cause rain. (thenextfamily.com)