I drew 2 cards, and drew storm first which told me that I would miss my next turn. Does my turn end there or do I encounter Mephistoteles also?

Rulebook, page 7:

Adventure Cards must be dealt with in the order determined
by their encounter number (the number at the bottom right
corner of the card).

The lowest number is tackled first, then the next lowest, and
so on. In the case of a tie, the character encounters Adventure
Cards in the order they were drawn.

It looks like you've got this rule. So, if you've drawn Storm first, it is encountered first and your turn immediately ends.

Consider also what's written on page 16:

Losing a Turn

Any instructions that result in the loss of a turn by the character
encountering them ends the character’s turn immediately.
This counts as a missed turn for that character if there
are other cards to be encountered ; otherwise, he misses his
next turn instead.

You don't encounter Mephistopheles, so this counts as a your missed turn. After other characters have missed their turn according to Storm card instructions, you get to play again.

If the example happens while all characters are in the Outer Region, in this case everybody misses 1 turn and it's your turn again, because you didn't encounter a card (Mephistopheles).