Today likely marks the 38th 90 degree day of the year in Philadelphia. While it's quite likely we do not match the same number of 90 degree days set in the summer of 2010, we are likely just two 90 degree days from hitting 40 for the second summer in three years. In terms of 90 degree days, this year will nudge to a tie for 10th on the list of most 90 degree days in a year with 1953.
Above 1953 is 1941 (not listed), a year that had 39 90 degree days. It's possible that we tie 1941 tomorrow if we hit 90 again.
In terms of heat in "patterns", between 1988 and 1995 we had four years of 40 or more 90 degree days and one other with more than 30 (1994). We didn't approach 1995's total of 90 degree days again until 2002, with 1998 (31) and 1999 (35) flirting in the ballpark for 90 degree days. After 2002, we didn't exceed 30 90 degree days in a calendar year again until 2010 and now have exceeded 30 90 degree days each of the past three years. We're likely in another "cycle" of heat similar to that of the late 80's and the first half of the 1990's, with years where we will get plenty of hot days in the summer.
We probably get to 40 90 degree days before year's end -- we still have a month of potential 90 degree weather ahead of us and historically we average two 90 degree days after September 1st -- but it does rather likely that a top five summer in numbers of 90 degree days is not likely...and I think we can safely assume that we won't cross the 50 barrier as well. If you hate heat, at least you can take comfort in that fact.