B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 120; Flight Crew Type 1050
Situational Awareness; Communication Breakdown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification
Weather; Procedure; Airspace Structure
Level at 21;000 feet on the arrival; Aircraft X took a 125 degree heading to deviate for weather. We were shooting a narrow gap between two radar returns. We had been on this heading approximately 20 miles; and were just penetrating the gap; when ARTCC issued a turn 30 degrees to the right; without explanation. We replied; 'Unable'; as to make that turn at that point would put us directly into the cell on our right that we were avoiding. At this time; we also observed traffic on our TCAS; approximately 10 miles distance at our 11 o'clock; 200 feet below our altitude and descending. Approximately 30 seconds elapsed; as we watched the TCAS traffic descend below our altitude. The next transmission we received from ARTCC was; 'I know you're deviating for weather; but when I tell you to turn; it's important.' We chose not to engage in further discussion of this matter over the radio. Clearing the weather; we proceeded direct to [fix]; and completed the rest of the arrival; approach and landing normally.
Aircraft deviating for weather was issued a right turn. The pilot had to refuse the clearance due to weather. The pilot observed traffic on their TCAS descending below them.