Refer to the METAR/TAF Conversion card.
Intensity or Proximity
and WEATHER PHENOMENA
+TSRA= Thunderstorm(s) with heavy rain.
@ Nate, it would do you good to read my referenced guide, the qualifier (- or +) attaches to the form of precipitation not to the Descriptor
Heavy Thunderstorm with rain shower
- means light, + means heavy, and nothing means moderate
TS = thunderstorm and RA = rain
I hope this has helped!