Date: 201705
Local time of day: 1201-1800
Location: ZMA.ARTCC, FL
Flight conditions: Marginal
Aircraft: Small Transport; Low Wing; 2 Turboprop Eng
Operating under: Part 91
Flight plan: IFR
Flight phase: Descent
Airspace: Class E ZMA
ATC / advisory: Center ZMA
Second aircraft: Large Transport
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Time Pressure
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Airspace Violation All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Company Policy; Airspace Structure; Human Factors; Weather; Procedure
Primary problem: Weather

Narrative: I was plugged in 2:20 hours with no break offer; working combined Sectors 21 and 01. About half of that time I had no Radar Assist. Due to weather over the middle of the state; all departures going to the west coast were re-routed. Then all the arrivals started deviating into my airspace and eventually some were re-routed via my sector. I'm not sure which arrivals since minimal information was given from supervisors. Aircraft that were pointed out were not doing what was coordinated and no re-coordination took place. Aircraft were in my airspace without point outs; just data blocks displayed. Late hand offs on re-routed arrival aircraft at cruise altitude above overflights. Then I was advised we needed 10 miles in trail to FLL. Then a decision was made to split the sector because it was going to get worse. I was not sure it was possible! Aircraft trying to get to LAS and LAX were taking up frequency time asking how long before they can turn west and then complaining about it; regardless as to how fast my speech rate was. I finally got a tracker position for about the last 20 minutes. Actually the whole session should be its own report!The actual event in this report occurred at the end. I had 3 arrivals re-routed which were high so I was hurrying their descent and vectoring them for the 10 miles in trail. The Assist saw Sector 42 was handing off aircraft X routed over MAYKO intersection which they need to cross at 5;000 feet. He called and asked them to take the aircraft over another fix since we had the arrival handing off to them. I am not sure what transpired in the coordination; but they did not re-route aircraft X and they said they would expedite them to 11;000 feet and I told the Assist to tell them 7;000 feet which he did.I originally assigned aircraft Y descent to 10;000 feet. When the coordination began with aircraft X; all I recall seeing was 11;000 feet in the data block so I stopped aircraft Y at 12;000 feet and started the handoff to the next sector. I do not recall the actual altitude aircraft X was out of; I don't think I looked at it at that moment; just saw the 11;000 in the data block and then the 7;000 feet. They took the handoff and I switched aircraft Y. After I switched them I noticed both aircraft were at the same altitude descending; roughly out of 14;000 feet. Then the conflict alert began and I tried to call for aircraft Y on the frequency to see if he was with me and if he was then take action; but he was not with me. I saw the Sector 42 controller turn aircraft X 20 degrees left and separation was never lost. Later the Operations Manager said they ended up with 7 miles. At that point traffic died down and my tracker relieved me.The Sector 42 controller advised their supervisor it was a NMAC; so I spoke with my supervisor and an investigation by the Operations Manager followed. After speaking with the Operations Manager he said since it was not even a Loss of separation he would make a note of the event as an internal Mandatory Occurrence report. Had Sector 42 taken aircraft X to the LAUTH intersection; especially since he was so high; this event would have been prevented.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Two Center Controllers reported working a busy sector with weather deviations and did not notice an aircraft overtaking another aircraft descending to the same altitude.