There is no proper "summer" or "winter" pressure. When the ambient temp is around 55 degrees (U.S. average) and the tires have been sitting for a while OUT of the sunlight, then you should air them to what is on the door jamb. If it says 33 psi...use 33 psi. Then don't worry about it.
'92 YJ - heavily modded
'96 ZJ - heavily modded
'05 KJ CRD Limited - 370 lb./ft. from a 4-cylinder and trail ready. Pure awesomeness.
'11 Mango Tango JKU Sport - Mods
'12 Dozer JKU Sport S - 6-speed - ACE rock rails - Max Tow package - Daystar spacers - 33x12.50 Duratracs