On her first day in post, Meri Huws says her role is about protecting the rights of Welsh speakers.
She says she will use her enforcement powers if necessary, but says her target won't be small businesses in predominantly English-speaking areas, the proverbial 'Chepstow chip shops.'
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The heaviest bursts are expected in the south and east, with some western areas either remaining dry or becoming dry by dawn.
Many places will start dry, but rain in the southeast will spread to most for a time overnight.
The family of Isaac Nash who went missing after being swept out to sea last summer have presented a cheque for £10,000 to the RNLI.