Unseasonably warm weather is affecting some northern parts of WA this week.

A ridge of high pressure over southern and central Australia is allowing a warm air mass to linger over the nation's northwest.

In Broome, warm southeasterly winds flowing off the land pushed the mercury up to 36.5 degrees at 2:30pm on Monday. This was their highest temperature this late in the season for 21 years.

Monday was also Broome's 6th consecutive day over 35 degrees, which is an unprecedented feat this far into May.

Broome's average maximum temperature at this time of year is 31.6 degrees, although every day this week is forecast to reach between 34 and 36 degrees.