Gulfstream V / G500 / G550
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 11000; Flight Crew Type 500
Conflict NMAC; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Airspace Structure; Human Factors; Weather
After leveling on the departure procedure at 1;700 feet MSL; we turned to a heading of 113 and initiated a climb per the departure procedure. Immediately after climb initiation we simultaneously received a TA then immediately switching to a level RA and also a traffic advisory from Tower. There was a VFR target at 12 o'clock and approximately a mile +300 feet (~2;100 MSL) that was initially a TA then a RA. After initiating a level off the TCAS switched to a climb RA which was then followed.We were not warned by Tower until the beginning of the TA/RA event. I visually picked up the PA28 in a steep left hand turn at 1/2 mile and 1 o'clock. The aircraft passed approximately 300 feet off the right wing. After passing the traffic at 2;100 feet we were immediately IMC. There was no possibility of the PA28 being 500 feet below the overcast base as VFR rules dictate. I did call the Tower for feedback after landing at destination; but was informed the supervisor was investigating and would return my call in the future. The VFR traffic was inbound from the south and was attempting to enter a left downwind I would guess. We were then transferred to departure control and the remainder of the flight was uneventful. It was difficult to visually acquire the PA28 due to rain and low ceilings.
G-550 Captain reported a TCAS RA and NMAC with a PA28 in marginal VFR conditions.