Onda vs. vaga
While both onda and vaga correspond to the English word "wave" regarding a physical body of water, their figurative usage for sudden rises in activity or intensity differs significantly between Brazil and Portugal. Brazil overwhelmingly favors onda for these contexts, whereas Portugal frequently uses vaga for distinct surges of events.
Onda
A2In Brazil, onda is the universal term for any sudden rise in activity, weather, or trends, covering everything from heat waves to crime waves. In Portugal, onda is also used, particularly for heat (onda de calor) or crime, but it often competes with vaga.
O Brasil está preocupado com uma nova onda de contaminações.
(Brazil is worried about a new wave of contaminations.)
Uma onda de frio intenso chegou ao sul do país ontem.
(A wave of intense cold arrived in the south of the country yesterday.)
Aquela onda de assaltos deixou os moradores assustados.
(That wave of robberies left the residents frightened.)
Eles estão surfando na onda do sucesso da empresa.
(They are riding the wave of the company's success.)
Vaga
B1In Portugal, vaga is commonly used to describe a distinct surge or spell of events, such as a cold snap, a wave of strikes, or the fourth wave of a pandemic. In Brazil, vaga almost exclusively refers to a vacancy (like a job opening or parking spot) and is rarely used to mean a surge of activity.
Portugal enfrentou a terceira vaga da pandemia com novas restrições.
(Portugal faced the third wave of the pandemic with new restrictions.)
Uma vaga de frio polar está prevista para a próxima semana em Lisboa.
(A polar cold wave is forecast for next week in Lisbon.)
A polícia tentou conter a vaga de protestos no centro da cidade.
(The police tried to contain the wave of protests in the city center.)
Esta vaga de despedimentos afetou a economia local.
(This wave of layoffs affected the local economy.)
Summary
Use onda for any type of figurative wave (heat, crime, trend) if you are speaking Brazilian Portuguese. If you are speaking European Portuguese, you should often use vaga for sequential surges (like virus waves or cold snaps), though onda remains correct for heat and general moods. Remember that in Brazil, vaga usually implies an empty space or job vacancy, not a surge of intensity.