Somehow gentrifying centre of Balham in an alarming way (13)

I believe the answer is:

frighteningly

I'm a little stuck... Click here to teach me more about this clue!

'in an alarming way' is the definition.
I can't tell whether this definition defines the answer.

'somehow gentrifying centre of balham' is the wordplay.
'somehow' is an anagram indicator.
'centre of' indicates the central letters.
The centre of 'balham' is 'lh'.
'gentrifying'+'lh'='gentrifyinglh'
'gentrifyinglh' anagrammed gives 'FRIGHTENINGLY'.

Can you help me to learn more?

I've seen this clue in The Guardian.

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