Air Tour pilot reported entering IMC on a VFR flight. Contacted ATC for vectors back to VFR conditions.

Narrative

As a single pilot flying a tour in with 6 passengers; I took off in VFR conditions and proceeded to do my standard tour route around the island. Prior to takeoff; I had checked the weather and radar reports. The weather was not perfect VFR conditions as usual around the island. However; the visibility was above VFR minimums and the ceiling was high enough to clear terrain with more than 1;000 feet of clearance around the island and my planned route of flight. There was some rain and cloud cover but nothing that indicated rapidly deteriorating conditions.After completing about 80% of my tour along the coast; the weather closed in quickly and I suddenly found myself in hard IMC. The coast of the island is nearly always clear so I had not expected to be enveloped in clouds so completely.I checked the ATIS and got the current weather at ZZZ about 5 minutes earlier. I then contacted the Tower saying my position was approximately 10 miles North of the airport and was currently in hard IMC. I asked for vectors to final but the Tower was unable to guide me to the airport. They instructed me to contact ZZZ Center which I did. ZZZ Center could not give me vectors either because I was at 4;000 feet MSL and they needed me to be at a minimum of 7;000 feet MSL. I was close to the field and wanted to maintain positive control of the airplane so I decided it would not be ideal to start a 3;000 feet climb at that time.My instrument flying skills were invaluable in maintaining control of the airplane. Focusing on the airspeed indicator and attitude indicator where the keys to maintaining altitude and avoiding a stall or spin.After weighing my options and hearing another pilot on the radio suggest it; I decided to advise ATC. ZZZ Center then instructed me to contact ZZZ Tower again.The Tower Controller gave me vectors towards the airport. After about 5 minutes; I was on the left downwind for Runway XX and could see the runway clearly. The Tower then gave me a clearance to land. Upon landing uneventfully; there were no injuries or damage to the aircraft or property.In hindsight; I should have canceled the flight as the weather was changing so rapidly. I learned a valuable lesson regarding the unique weather characteristics of flying around an island with weather conditions that change by the minute.I hesitated to advise ATC because I did not think I was in an [urgent] situation. In addition; I did not want my passengers to panic. They all heard my radio communications and despite advising ATC; all of them remained calm. I explained to them that we had plenty of fuel and there was nothing mechanically wrong with the airplane. After some deliberation; advising ATC was the only way for me to get back to the airport safely.