Bureau duty forecaster Helen Kirkup said the worst of the storms was expected to hit west of Canberra but urged residents be aware if conditions changed.

The system is unlikely to bring a deluge of rain, with the chance of up to 8mm on Thursday.

Ms Kirkup said if storms hit the ACT, the dry air mass would bring damaging winds.

The trough will move east on Friday with storms expected to hit the South Coast, however Ms Kirkup said it wasn't out of the question the ACT would see more storm action.

ACT Health has warned asthma sufferers to stay alert as it warned of a "thunderstorm asthma event" on Thursday and Friday.

"Thunderstorm asthma" is the triggering of an asthma attack by a thunderstorm.

The storm can act on pollen to make particles smaller and so, easier to breathe, and that increases the risk of asthma attacks.

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"Thunderstorm asthma can be triggered by a combination of high grass pollen levels and a particular type of thunderstorm, which causes some people to develop severe asthma symptoms over a short period of time," a statement from ACT Health said.

"Where possible avoid being outside during a thunderstorm - especially in the wind gusts that come before the storm. Go inside and close your doors and windows. If you have your air conditioning on, turn it onto recirculate.

"If you develop asthma symptoms, follow your asthma action plan. If you experience asthma symptoms that are not relieved by your usual asthma treatment, you should seek further urgent medical advice. In the event of a medical emergency you should call 000."

Sunny days will return by the weekend with a clear day and top of 23 expected on Saturday.

Sunday is set to be very warm, with a sunny top of 28 degrees forecast and a low of 8.