If you were up half the night in the hot, humid, sticky weather, you were not alone.

Parts of the North Island - and even Christchurch in the south - woke up to 99 per cent humidity this morning.

Temperatures didn't drop below 21C in Auckland and Tauranga last night, with more of the same forecast for the coming days.

Metservice lead meteorologist Mark Todd said the tropical weather was making New Zealand feel "more like the Cook Islands at the moment".

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Humans can adapt to humid weather after just a few weeks, but until that occurred we tend to find it harder to deal with than dry heat.

Humid weather affects our ability to sweat, our natural cooling system, and can affect our ability to sleep.

Drinking plenty of water is a good antidote to the heat, especially during exercise.

During the night, heat can increase how long it takes to get to sleep, and the number of times we wake during the night.

The sleep hormone melatonin helps regulate the sleep cycle by dropping the core body temperature. That process is interrupted when body temperature is too high.

A lack of sleep can affect mood and performance, and leave you feeling like you have a hangover in the morning.

The ideal temperature for sleeping is between 16C and 18C, and the worst temperatures are anything above 22C.

Much of the North Island is in for another hot night tonight, with an overnight low of 21C forecast for Whangarei, Auckland, Tauranga, Hamilton and Napier.

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The South Island should be sleeping alright though, with overnight temperatures as low as 10C tonight in Queenstown, even dropping to a chilly 9C tomorrow night.

To help keep your bedroom cool, stop it from heating up in the day by keeping the windows, doors and curtains closed - keeping the cool air inside - and opening them up in the evening.

Obvious tips include using airconditioning, a fan or a dehumidifier, while the more adventurous types might want to try placing a bowl of ice in front of a fan.

Another less obvious tip is to point a fan out the window, which will blow the hot air out and cool the air coming in.

Keeping the house dry in humid weather could also be a challenge.

Energywise said extractor fans that vented outside the bathroom, kitchen and laundry were useful.

Even though it was wet outside, avoid drying clothes and towels inside. Try and find a covered area outside or in the garage.

Keep furniture away from external walls with at least a 10cm gap - especially if they are uninsulated.

Keep mattresses off the floor and leave wardrobes slightly open for ventilation.

Tips to keep cool

• Keep the cool air inside and sun out by closing doors, shutting windows and pulling curtains during the day.

• Open windows and doors in the evening to let the cool air in.

• Use a fan/air conditioning, even try facing a fan outside the window to blow hot air out.

• Drink plenty of water.