Widebody Transport
Flight Crew Air Transport Pilot (ATP)
Distraction; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Weather; Human Factors; Aircraft
Uneventful descent into Miami while avoiding thunderstorms. Vectors to intercept final course for RNAV/GPS Rwy 26R. We kept the speed up to get on the ground before a series of thunderstorms got to the airport and received shortened vectors to final inside the NAYIB fix on the approach. On final and after confirming FMS speed; Nav; and profile MDA; while consulting with each other about rain showers close to the airport; we noticed that the airplane was descending below the profile glidepath and I disconnected the Autopilot to arrest the descent. We descended to 1300; below the minimum 1500 ft for that portion of the approach before the Final Approach Fix ZARER. We immediately started a correction back to published altitude. At that point we received a yellow GROUND PROXIMITY alert for several buildings 2 to 3 miles in front and on both sides of the approach course. After confirming we were well clear of all obstacles and still in a safe position for landing we opted to visually continue the approach and landing. Distraction with weather during the approach. Clarify before the approach the duties (i.e. who will be looking at the radar and who will be closely monitoring the instruments).
[Report narrative contained no additional information.]
Air carrier flight crew reported descending below the MIA Runway 26R RNAV Approach profile. The autopilot did not capture the vertical path and the crew did not detect it until they were low causing a GPWS warning.