It happens every year.. ...... I HAVE to start my tomatoes early so they will have time to make fruit before the big heat wave comes in.  Tomatoes will not pollinate very well in the heat and humidity.  This year I tried very hard to hold back so that if we needed to cover the plants they  would not be HUGE like last year.  When I woke to check them the temp was 40.. currently it is 36.  I think we will be just fine!  Last year I had ALL my plants out and we had a 3 day frost.  I considered standing outside with my hairdryer   It was not good for my nerves.  I only lost 1 plant.  I did not see that the tarp had curled on the edge and it was on the perimeter.  They had a HUGE TENT tarp over them and a heater for 3 days!  I fretted and paced and fretted..but in the end I had a bumper crop of tomatoes.