A321
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Took Evasive Action
Weather
Weather was all around the area but not on the field. Weather was 10 miles ahead on the departure. We expected deviation around it because it looked severe. After contacting departure in the initial climbout we asked for deviation left or right. The controller said 'unable.' The radar returns were red and looked severe. 'Unable' was not a good enough option. Looking outside the front windscreen we saw black cumulous type thunderstorm clouds to back up the radar. ATC was very busy and too busy to argue. We had to make a decision. We decided; for safety of the aircraft and passengers to deviate slightly to the left to avoid the brunt of the storm. After going about 0.4 or 0.5 miles left we were told by ATC that we looked off course. We acknowledged our deviation; and were told to get ready to copy a number for a possible pilot deviation. We had no ride report information or the ability to get a word in and ask for one. We made a decision based on what we thought was safest; with the information we had at the time. We decided to not put the lives of people at risk flying through a severe storm at a low altitude. We had no TCAS events at all.The event was due to us expecting deviation around weather and not being given enough information to work with. We should have been informed of ride reports and weather ahead. Airborne weather radar does not give reliable enough returns to see the total severity of a storm from the ground.Close the departure; issue vectors; or tell us ride reports or how other aircraft are getting around it before takeoff. These are all things that are provided at other ATC facilities so running a normal departure sequence into weather; we expected to get vectors like all the other aircraft ahead of us.
A321 First Officer reported deviating for weather without ATC clearance.