Ten people died during or soon after a thunderstorm asthma event in Melbourne on November 21, 2016.

Deputy chief health officer Allen Cheng noted the freak storm, which prompted an inquest, in his warning to the public on Thursday.

A combination of high pollen levels and strong winds can trigger the phenomenon.

November is usually the peak period for the asthma event, but Dr Cheng said it could take place any time from October to December.

The Bureau of Meteorology confirmed a La Nina over the Pacific Ocean on Tuesday, meaning Australia is likely to have a rainy spring and summer.

There is the possibility of flooding and more severe tropical cyclones than usual.

"This is likely to mean that it is somewhat of a high risk of thunderstorms, although the pollen forecast at this stage is only that it is probably going to be moderate," Dr Cheng told reporters.

Current, former or undiagnosed asthmatics and hay fever sufferers should stay indoors when high-risk epidemic thunderstorm asthma events happen, or they should have good control of their condition.

"If you are in any one of those groups, you should see your GP and make sure that you have an action plan in case something happens," Dr Cheng said.

"There have been a lot of changes to recommendations about medications over the last year.

"Even if you have seen your GP, but haven't seen them for a little while, it may be worth going back to make sure the medication you are on is appropriate."

Dr Cheng said concerned Victorians could check pollen count meters on the VicEmergency app and University of Melbourne website.

He assured the community that systems were ready to issue high pollen warnings and monitor hospital admissions for signs of epidemic thunderstorm asthma.

Australian Associated Press