The mercury hasn’t dropped below the 40°C mark since June 1 and chances that it would do so in the next one week are remote. This is the longest spell of temperature remaining above 40°C during the first 10 days of June, at least this decade. Since 2011, while in all other years Delhi received at least a day of rain in the first 10 days of June, there has been none so far this month. Delhi last got rain on May 15.The India Meteorological Department (IMD) has, however, forecast that there could be some respite from Tuesday as there are chances of dust storm and thunderstorm and may bring down temperatures by two degrees. “No rain almost over the past month in the national capital and extremely high temperature across northwest India is helping heat build up in Delhi and NCR,” said a senior official of the regional weather forecasting centre (RWFC) in Delhi.The temperature at the Safdarjung observatory, which is taken to be a representative of Delhi, was recorded at 45.6°C, six degrees above normal. Also read: Mercury rises again; thunderstorm likely to hit Gurugram tomorrowIt was the highest temperature recorded in the month of June since 2003. At Palam the maximum temperature was recorded 48°C on Monday. It was the second highest temperature ever recorded in Palam. “The highest temperature ever recorded in Palam was on May 26, 1998. It was 48.4°C,” said an official of the RWFC. “While Safdarjung, where the temperature was at least six degrees above normal, registered a heat wave, at Palam where the temperature was eight degrees above normal, we have declared a severe heat wave,” said an IMD official. The IMD declares a heatwave when the maximum temperature in an area hovers above 40°C and it is at least 4.5°C above normal. If the temperature is 45°C or more, then the meteorological department declares it as a heat wave straightway. A “severe heat wave” is a condition when the maximum temperature in a location hits 47°C. Senior officials said that even though monsoon usually arrives in Delhi around June 29, this year it is expected only in the first week of July.