Corporate jet Captain reported being established on the RNAV GPS to Runway 28L at HWD Airport but received a TA from a VFR general aviation aircraft that was not in communication with ATC. The reporter stated that this was a common problem as VFR traffic use this corridor to avoid controlled airspace and terrain.

Narrative

We were established on the RNAV GPS to HWD 28L. IMC on the final approach course and LPV path; but observed TCAS traffic ahead about 3 NM and 1000 feet below. While IMC ATC advised us of the traffic; and advised they were not talking to them. We broke out at approximately 3900 MSL and acquired the VFR Aircraft Y at about 2 NM on a converging course; but below. Advised ATC that we had the traffic at 11 o'clock and converging in sight; and the airport. ATC cleared us for the visual 28L. About 2 seconds later we got a TA; followed by a TCAS RA about 3 seconds later. We had the traffic in sight; without conflict but still complied with the RA. The VFR traffic passed under our nose about 300 feet below. Once clear of the conflict we continued the visual approach.This is a common problem at this location. VFR traffic use this corridor to avoid Class B; C; and D airspace; as well as local terrain; often with minimal cloud clearance. The airspace design funnels VFR aircraft to this point; and they rarely are in radio communication with anyone. If on the approach IMC to HWD it is not uncommon for ATC to cancel your approach clearance and vector you back around for another. If on the approach and you break out it is immediately a priority to scan for VFR traffic. RAs happen regularly; especially on the weekends during daylight hours.