the pawn storm attack to open pathways to the enemy king is the whole point of opposite side castling. if you want a more positional game then just castle on the same side. the one exception to this is main line Najdorfs with opposite side castling, where positional understanding plays a huge role alongside the base race.
Is a pawn storm necessary after opposite-side castling.

Ah, the dreaded pawn storms.
"...The very moment you have castled, the opponent's pawns vehemently and vigorously lurch in your newly-castled king's general direction. You immediately and instantly lose whatever initiative you might have had, have to drop whatever you were doing or planning to do, and can only hope that you might just possibly manage to exchange your castle pawns for the stormers once they arrive, rather than just losing them and seeing your king be cooked like an egg on a frying pan, if the storming pawns manage to receive enough support from their allied pieces..."
...brrr.

A pawn storm isn't always necessary or even correct. It's a very patzerish way to think. Just search a database for GM games with opposite side castling and you will see that they are not always races between attacks on different sides. Even in an opening like the Yugoslav Attack of the Dragon Sicilian there are some typical positional ideas often featuring exchange of queens.
On the other hand, there are also lots of positions where a pawn storm against the opponents king is clearly the correct plan. In particular, it's rarely possible to stay passive and try to hold the position if the opponent launches such an attack. You will need counterplay. Usually either in the center or in the form of your own attack. If the centre is closed then a pawn storm may be all you are left with. Also, in some closed positions with opposite side castling it is more natural to attack on the same wing where your king is located (this is quite typical in KID).

You are an spaghetti, yellow as my hair.
Why are you worried about chess?
And no, there is no way to play in opposite side castlings without pawn storms as the goal of the game is to checkmate the enemy king.


It is perhaps more usual but in structures where black e5 and white d5 is played it sometimes happens that because of the black space advantage on the kingside it's difficult for white to play there and vice versa on the queenside. The next example may not be the best but it nevertheless illustrates this theme. White lands the final blow on the kingside but this is only after most black pieces have been tied to the defence of the queenside.
Opposite-side castling without any obvious (semi) open files always seems to turn into a race on both sides of the board for me.
But is this always necessary? Shouldn't there be some reliable way to hold the position without launching into an equally aggressive and sharp counterplay with pawns at the other side?