Australia's Top End is experiencing a record breaking heatwave, with Darwin sweating through its second-highest temperature on record.

The mercury hit 38.2 degrees in the capital at 12.30pm on Monday, the third time it has topped 38C in almost 40 years.

The hottest ever day recorded in Darwin was 38.9C on October 18, 1982.

October and November are traditionally the hottest months in the Top End, but a heatwave is producing temperatures well above the long-term average of 33.3 degrees in both months.

Other areas in the Top End have posted their hottest days on record in recent days, including 42.7 degrees last Thursday at the Tindal RAAF base near Katherine.

There has been no rain recorded in October; the average for the month is 70mm.

While it is currently the so-called "build up, troppo" period between the Top End's dry and wet seasons, some rain has usually fallen by now.

There has been virtually no rain in the Northern Territory for the last 156 days, since some unseasonal tropical thunderstorms in May.

The longest dry run was 167 days in 2008.

A slight fall in temperatures for the forthcoming weekend and higher humidity might lead to some long awaited relief with some showers, Bureau of Meteorology spokeswoman Jude Scott said.

Like most parts of Australia, the NT is trending hotter.

Last year's wet season was the hottest on record and driest in 27 years, with total rainfall just two-thirds of the average.

The outlook for this wet season is for fewer than average tropical cyclones in the NT, but a good chance of two or three forecast.