I took my special needs son to dinner via our boat crossing Lake Pontchartrain from Mandeville, Louisiana  to New Orleans, a 1.5 hour trip one way. On our way back I was aware of a storm that was developing to our north east but on the radar it was not in the lake yet, and future cast radar feature showed it would not interfere with our return trip. The radar location of the storm was wrong as was the future cast. By the time we reached the middle of the lake heading back at sunset this storm was on top of us. Wind was gusting 40 plus mph, rain was pounding, very strong waves were building, lightning all around us, and then the sun set completely putting us in complete darkness. My visibility was limited to my control panel lights, other than during the lightning flashes where I could see waves bigger than our 22 foot boat. I feared for our lives and was sure I could not keep us afloat much longer in the storm, so I activated our EPIRB and made a Mayday call over the radio. The Coast Guard responded, and thanks to our EPIRB was able to pinpoint our location and send rescue. It did take almost 2 hours for them to reach us because they were already responding to 5 others boaters in the same situation before us.