The Meteorological Centre in Lucknow has issued a red alert for 10 districts in Uttar Pradesh for Friday, warning of "severe" to "very severe" heatwave conditions, and temperatures in more than 15 districts of Tamil Nadu have crossed 39° Celsius.

The red alert in UP has been issued for Banda, Chitrakoot, Kaushambi, Prayagraj, Fatehpur, Pratapgarh, Mirzapur, Varanasi, Bhadohi and Jaunpur districts, where severe heatwave conditions are likely during the day.

An orange alert has been sounded for 34 UP districts, including Baghpat, Meerut, Ghaziabad, Hapur, Gautam Buddh Nagar, Bulandshahr, Aligarh, Mathura, and Agra.

The weather office has also issued a yellow alert for 17 districts, including Deoria, Lakhimpur Kheri, Sitapur, Hardoi, Farrukhabad, Lucknow, Barabanki, and Ayodhya.

The Met department said maximum temperatures are likely to rise gradually by 2-3°Celsius in eastern Uttar Pradesh over the next 48 hours, while no major change is expected elsewhere during the week.

Under the warning classification issued by the weather office, a yellow alert means people should remain updated, as heatwave conditions may persist for two days.

An orange alert advises residents and authorities to remain prepared as severe heatwave conditions may continue for two days or heatwave conditions of varying intensity may persist for four days or more.

A red alert calls for immediate action as severe heatwave conditions are likely to continue for more than two days and pose a serious risk to public health.

An intense heatwave swept Uttar Pradesh on Thursday, with Banda recording the highest maximum temperature in the state at 47.6° Celsius.

Prayagraj recorded 46.6° Celsius, followed by Varanasi (BHU) at 45.6° Celsius, Sultanpur and Hamirpur at 45.2° Celsius each, Fursatganj at 45.1° Celsius and Jhansi at 44.8° Celsius.

Lucknow recorded a maximum temperature of 43.6° Celsius, 3.4° above normal, while the minimum temperature settled at 29° Celsius, 3.5° above normal.

The city reported maximum relative humidity of 59 per cent and minimum humidity of 15 per cent, according to the MeT.

UP chief minister Yogi Adityanath has directed all departments to remain on full alert and ensure measures to prevent heat-related illnesses, while instructing district administrations, hospitals, power and relief departments to maintain adequate stocks of medicines, beds, IV fluids, drinking water and round-the-clock ambulance services, besides ensuring preparedness against fires.

The India Meteorological Department has attributed the prevailing extreme conditions to the absence of any active weather system, clear skies leading to enhanced radiational heating and hot, dry westerly winds.

Chennai has hottest summer day so far

In Tamil Nadu, Chennai recorded the highest of 42° Celsius this summer on Wednesday. The weather office has warned that hot conditions are likely to persist.

A bulletin of the Regional Meteorological Centre on Friday said heatwave conditions are expected to prevail over coastal Tamil Nadu and Puducherry.

High daytime temperature combined with humidity is likely to cause discomfort in these regions till Saturday.

The bulletin has also forecast heavy rain, in isolated places, accompanied by thunderstorm, lightning and gusty winds reaching 40-50 kmph over Tiruvannamalai, Tiruchirappalli, Salem, Namakkal, Vellore, Tirupattur and Dharmapuri districts from Saturday.

During the last 24 hours, Aranthangi in Pudukkottai district recorded maximum rainfall of 5 cm followed by Karaikudi in Sivagangai district, Nagudi in Pudukkottai district, and Neyyoor in Kanyakumari district three each.