The Met office said the unrelenting heat wave - that swept through Patna and most parts of Bihar for the sixth day on Thursday, worsened with a surge in relative humidity - would continue for another three days, with little chance of thundershowers to bring respite.

The Telegraph highlights how the current spell is different from a normal Patna summer and why people need to be wary.

How hot was Patna on Thursday?

The maximum temperature witnessed a surge of 0.3ºC in the past 24 hours as the patches of clouds seen above the on Wednesday cleared at night. Tuesday was the hottest April day in Patna in a decade with the maximum temperature at 44.1ºC; on Wednesday it was 43.6ºC - still seven notches higher than normal.

Why has Patna become abnormally hot?

Gradual warming of the central parts of the country is causing the neighbouring region, including Bihar, to heat up excessively. On a larger perspective, the higher sea surface temperature in the Indian Ocean - two-three degrees higher than normal - is still to cool down completely. This has led to 1.5-2° Celsius higher seasonal temperature in eastern and central India this summer.

How does Patna compare with other cities known for high temperatures?

In Chennai, the temperature was 35.9°C at 2pm but the RealFeel index went up to 45 degrees because of high humidity. Bhubaneswar touched 45.3ºC at noon, breaking its all-time record of 45ºC for highest maximum temperature in April. Calcutta was a tad cooler as the maximum temperature stood at 37.1ºC. Even the desert cities of Abu Dhabi (38ºC at 1pm with a RealFeel of 42°C) and Jaisalmer (42°C at 3pm with a RealFeel of 45°C) were cooler.

What is the weather forecast till the weekend?

All of Bihar will reel from heat wave conditions. "Central and western Bihar would face severe heat wave," said Ashish Sen, director, Patna Meteorological Centre.

"Rest of the state would brave a moderate heat wave." According to the revised rules of India Meteorological Department, "severe" heat wave is declared when the temperature of a place is 6.4°C above normal.

Can residents expect some showers?

R.K. Giri, senior meteorologist at Patna Meteorological Centre, said showers are expected around May 4.

"A western disturbance is expected to reach Jammu and Kashmir on May 1 and move towards Nepal thereafter. This would lead to moisture incursion in Bihar as well, which may translate into light rainfall, primarily in the western parts of the state," said Giri. All of Bihar is expected to witness partly cloudy conditions under the influence of the upcoming weather system, which would drag down the temperature but the discomfort level due will rise due to rise in humidity level.

Why is it still comfortable indoors?

Higher the temperature, the more the people sweat; but humidity is quite low in Patna (between 5-25 per cent). So, residents - especially those avoiding direct sunlight, staying indoors or under a shade - are not feeling too uncomfortable. Wednesday could have been slightly uncomfortable because the relative humidity was comparatively higher - up to 33 per cent.

What causes heat stroke?

Heat stroke occurs when the portion of the brain that regulates body temperature begins to malfunction because of excessive heat. The enzymes of the central nervous system are programmed to work within a certain temperature range. Once that range is crossed, the enzymes malfunction. The body temperature keeps mounting along with fluid loss, and can lead to cardiovascular collapse, multi-organ failure and even death. The elderly and children are especially susceptible to heat stroke.

What are the symptoms?

When body temperature shoots up beyond 104°F, a person experiences headache and nausea. Heartbeat increases, breathing is rapid and flushing occurs. The patient also becomes incoherent. Immediate hospitalisation is advised.

What precautions should you take?

Doctors advise spending some time in room temperature before turning the AC on, wearing light-coloured cotton clothes and covering as much skin as possible. Have light meals and watery fruits. Use sunscreen, wear shades and protect the head from direct sunlight.