A heat-wave is a period of abnormally high temperatures, more than the normal maximum temperature.
The India Meteorological Department warned that the average temperatures in most parts of India are expected to be "above normal" between April and June, the period it considers the actual summer season.
The IMD, however, said the temperatures in east, east-central and southern India, which include Odisha, coastal Andhra Pradesh and Telangana, are likely to be lower than the usual, indicating that the onset of monsoon will be on time.
The "above normal" average temperatures prediction suggests that the warming of the summer season in northern and central India would be a continuation of the pattern seen over the past few years.
Last year was recorded as the hottest year so far by the IMD and other meteorological institutes across the country.
The previous year, 2016, was recorded as the hottest year since 1901. That year, Phalodi in Rajasthan had recorded 51 degrees Celsius, the highest-ever recorded in India by then.
The respite, according to the IMD prediction, is that the this year's average temperature, despite being "above normal" in most parts of India, would be slightly lower than 2017.
"Upcoming Hot Weather Season (April to June-AMJ) is expected to have the above normal sub-divisional average seasonal temperatures over most of the meteorological subdivisions of the country except the subdivisions of eastern, east central and southern parts for the country that are likely to experience slightly below normal seasonal temperatures," the IMD said in a bulletin.
It was the second seasonal forecast issued by the IMD for the upcoming summer season.
The mercury has started rocketing, reaching 40 degrees Celsius in parts of India, including in Delhi, in March, which is not considered as the summer season. This had prompted the meteorological department to issue a forecast on February 28.
IMD Director-General K J Ramesh said thunderstorms in east, east-central and southern India will keep these parts generally cooler.
"This is also an indication that the onset of monsoon will be on time," M Rajeevan, secretary, Ministry of Earth Sciences, said.
Severe heat-wave conditions in Odisha, Andhra Pradesh and Telangana have killed thousands of people over the past a few years. According to a government data released last year, 4,624 people died due to heat-wave between 2013 and 2017, of which 92 per cent of casualties were reported from Andhra Pradesh and Telangana.
"The AMJ seasonal average temperatures in most of the meteorological subdivisions are likely to be cooler than that of last year. Normal heatwave conditions are likely over core heat-wave zone of the country," the IMD bulletin added.
This, however, does not mean there will be no heat-waves this year. "Usually, there are three-four heat-waves every year. This year, we expect it to remain the same," Rajeevan added.
Central and northern India are generally considered the core heat-wave zones.
A heat-wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the north-western parts of India, according to information available on the website of the National Disaster Management Authority (NDMA).