I wish I had better news for you. Right now it looks like the Fourth could be quite stormy with a widespread coverage of showers and storms or even a steady rainfall. Temperatures would be much lower if this does in fact come as a steady shield of rain. Temperatures would probably not get out of the mid 60's, but for now I think there will be some dry periods which will allow the temperature to get into the low 70's. It looks like the rain could be long lasting with the warm front taking a while to get through all of SNE. After the front moves through Wednesday night and into Thursday, the rain will definitely become less widespread and it will become much more showery. Thunderstorms will be more prevalent as well with increasing humidity.
First, tomorrow will be remincent of mid to late September. Early morning temperatures in the suburbs will likely be right around 50 degrees. Highs will only make it to around 70 degrees with abundant sunshine. It will feel crisp and make you think we are heading towards Labor or Columbus Day, not Independence Day. Tuesday will be a tad warmer with highs in the mid to upper 70's before the mess for Wednesday through Thursday. Just throwing it out there, but the rainfall totals could be quite significant.
Right now I would say that in this two day period we could be seeing about 1-3" of rainfall, heaviest in SNE, away from the South Coast, Cape and Islands. If we do see thunderstorm coverage, the rainfall totals could be more significant and 3"+ totals would be localized and localized flooding could become an issue.
I know that you do not want to hear this for your Fourth of July plans, but it is something that looks nearly certain at this time. We will have to make our plans accordingly and outdoor BBQ's could be put in jeopardy. I remember the last real rainy Fourth. I believe it was back in 1996. July 4, 1996 was a miserable day with heavy rains and cool temperatures. It was also the day the movie Independence Day came out and everyone went to go see it that night. The theaters were packed. Another movie Fourth? Maybe, but don't scrap plans just yet. Maybe we can push this whole mess to Thursday.