Count If Measure For Last 3 Months Above Value

I have a table of data that is in the format below:

I need to calculate how many categories have  achieved a % value >= 20% for the last 3 consecutive months rolling. So in the example above for Nov the count should be 1 (category A) as the % value was >= 20% for the last 3 months rolling. 
I'm not sure what the best way is to achieve this? I was thinking if I ended up with something like below than I can just sum the 3rd column for each of the months so for Oct there is 1 category that ended up achieving >= 20% for previous 3 months and for November there is also 1 category that ended up achieving >=20% for previous 3 months. 

But if anyone has any better ideas? The Month value is from a date calendar, so it not initially grouped by month. I need the % value grouped by month before summing them over the 3 months rolling.