B737 Undifferentiated or Other Model
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 184; Flight Crew Type 1200
Communication Breakdown; Time Pressure
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Human Factors; Weather
Challenging flight conditions anticipated with thunderstorms in the ZZZ area; ZZZ1 area; as well as along route. Significant turbulence along route; destination short; wet runway; 6000 ft - abrupt braking; terrain; night; challenges with landing performance with required fuel load; cabin discrepancies. Flight was listed to depart out of C gates; travel from B to C gates; flight gate change to XXX; traveled back to B gates. Upon reaching the final gate; XXX. This had everyone; pilots; F/As (Flight Attendant); passengers; moving at a quick pace that needed consideration.Before boarding the aircraft; I indicated to the CSR (Customer Service Representative) agent that I needed 5 minutes to conduct a thorough briefing to all of the flight attendants as this was going to be a challenging flight. I indicated that I would walk back to the CSR podium when we were done. He indicated in the affirmative.I began my briefing to the flight attendants; and less than a minute later; some of the passengers appeared at the cabin door. I terminated my briefing; welcomed the first passengers; and walked back to the CSR podium. There was a CSR Supervisor present; and I asked why boarding had been initiated? The CSR Supervisor indicated that it is their policy to begin boarding as soon as the aircraft is cleaned. I articulated again that I had needed only a few minutes to conduct a safety brief with the flight attendants. She indicated that that was not her problem. I indicated that I am responsible for safety.  The CSR Supervisor indicated that once the cabin door is shut with the passengers boarded; then it is 'your' airplane; but not before.I calmly walked to the podium; utilized the PA (Public Address) system; and indicated to the passengers that we are going to stop boarding until our final Safety Checks are complete. I returned to the aircraft; briefed two flight attendants at a time on the flight deck - two briefs - then returned to the podium and utilized the PA system to announce to the passengers that we were ready to re-initiate boarding.Remainder of flight nominal. I cannot overemphasize the importance of a thorough Flight Attendant briefing when conditions are challenging. Additionally; when the pace has been virtually frantic at the airport; it is imperative that an assessment of the crew and moment to regain full situational awareness is paramount. This was not a flight from ZZZ2 to ZZZ3 in the daytime with no weather - this was extremely challenging; and my critical time with the flight attendants was interrupted. Although I recovered from this interruption by curtailing boarding; compartmentalizing; and individual briefing the flight attendants; a very serious concern is our CSR personnel's lack of awareness of Captain's authority; and their perceived favor of dependability over safety.
B737 Captain reported extreme weather delaying flight and requested passenger boarding to be delayed until briefing was held with cabin crew.