Date: 201901
Local time of day: 1201-1800
Location: MMUN.Airport, FO
Flight conditions: Marginal
Weather elements / visibility: Thunderstorm; Turbulence
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach; Landing
ATC / advisory: Tower MMUN
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure
Second reporter function: Captain; Pilot Not Flying
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Landing Without Clearance; Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition
Contributing factors: Weather
Primary problem: Weather

Narrative: Flight [to] MMUN; NOSAT 1B arrival. CZM as Alternate. I was pilot flying. Held at LETIS on the arrival for approximately 20 minutes due to weather in MMUN area. Cleared to airport for ILS 12L via Radar Vectors to the North for Weather avoidance. Encountered moderate turbulence during vectoring while avoiding scattered cells. Vectored near the FAF to avoid weather for the ILS. In visual conditions but due to the vectoring altitudes; I was unable to get the airplane fully configured by 1;000; so I initiated a Go-Around. During subsequent vectors to the southwest for another approach to 12L we encountered moderate turbulence again. The Flight Attendants (FA's) called to inform us they had a Pregnant woman who was unconscious and needed immediate medical assistance - requesting Paramedics.I told the Captain that I did not want to attempt another approach under these conditions and that we should divert to CZM. The Captain agreed and asked for vectors clear of weather and to divert to CZM. During the vectoring; which took us out over the water to the East to the airport and clear of the weather; ATC informed us that the airport was now landing to the northwest on Runway 30L and asked if we wanted to fly the RNAV to 30L. The approach corridor to the airport was clear of weather / turbulence and the winds were from the northwest; so we requested the approach for 30L. On the approach; we broke out at approximately 1;000 with good visibility; no precipitation and slowed to follow a Lear Jet ahead of us. Captain asked for landing clearance and was told to continue due to landing traffic. At approximately 500 feet; Captain again asked for landing clearance and Tower instructed a Go-Around. Captain responded that we were unable. The Captain instructed me - if the traffic clears the runway; we are landing.At approximately 300 feet; we could both see the Lear Jet clearing the runway. Tower instructing again for a Go-Around and Captain stated unable; we must land. The Captain said the traffic is clear of the runway - I agreed. He gave me a direct order - Do not Go-Around - Land the Airplane! The traffic had cleared the runway prior to our landing. I assume that the Captain based his decision on several factors:•	Fuel State•	Known weather / turbulence in Missed Approach path•	Unconscious pregnant woman•	Previous approach / missed approach into weather•	I believe Landing was a reasonable exercise of Captain's Authority.Cause: I believe that ATC did not space us correctly with the Lear during a switch to a non-normal traffic flow into MMUN. The Lear was very slow to clear the runway. Suggestions:1.	Divert early2.	[Identify as an] priority to ATC


Second narrative: We had a pregnant woman; unconscious; needing emergency medical care. We broke out of the weather at 900 feet. The preceding aircraft was still on the runway but slowly clearing. Cancun Tower directed a go-around at 500 feet. I directed the copilot to continue and informed tower. The aircraft was completely clear as we passed through 200 feet. We landed and proceeded to the gate with awaiting paramedics. The woman [was] helped and she recovered.We should have immediately [identified as] a medical situation with MMUN to get priority. Time and weather conditions prevented this. The preceding aircraft still on the runway was an unexpected surprise.Safety was never jeopardized. The runway was well clear when we landed.


Synopsis: B737 flight crew reported exercising Captain's authority during landing after tower instructed a go-around.