The dry season is finally arriving in the Top End after the equal hottest May nights on record, the Bureau of Meteorology says.

May has been unseasonally wet and humid but a cool dry change this morning saw the temperature drop to 22 degrees.

The bureau's Todd Smith says it will be even colder tonight.

"In fact, tonight we're going for the first minimum to dip below 20 degrees for the year," he said.

"That's always a good sign that the dry season is arriving and people need to air out their doonas to cope with the 19 degree temperature."

Mr Smith says even with the cool change, May will equal the warmest on record.

"In terms of night-time temperatures, it's been equal warmest ever, he said.

The last time we averaged 24.3 overnight was May 1978.

In terms of rainfall, it's been the wettest May since 1997 so it's been quite unusual in terms of humidity.

It's been the most humid May since 1968.