<span style="color: #222222;">The ongoing heat wave spell tightened its grip on parts of Delhi on Sunday, with the mercury breaching the 45-degree Celsius mark in six localities. The Met Office has issued a yellow alert, warning of heat wave conditions at isolated places in Delhi on Monday.<br />''<br />''At the Safdarjung Observatory, the city's base station, the maximum temperature settled at 44.2 degrees Celsius as against 43.9 degrees Celsius on Saturday and 42.9 degrees Celsius on Friday.<br />''<br />''The mercury jumped to 47.3 degrees, seven notches above normal, at Mungeshpur, making it the hottest place in the capital.<br />''<br />''Sports Complex, Pitampura, Najafgarh, Jafarpur and Ridge recorded a high of 46.6 degrees Celsius, 46.2 degrees Celsius, 46.3 degrees Celsius, 45.1 degrees Celsius and 45.7 degrees Celsius respectively.<br />''<br />''The India Meteorological Department uses four colour codes for weather warnings — "green" (no action needed), "yellow" (watch and stay updated), "orange" (be prepared) and "red" (take action).<br />''<br />''A heat wave is declared when the maximum temperature is over 40 degrees Celsius and at least 4.5 notches above normal. A severe heat wave is declared if the departure from normal temperature is by more than 6.4 notches, according to the IMD.<br />''Based on the absolute recorded temperatures, a heat wave is declared when an area logs a maximum temperature of 45 degrees Celsius.<br />''<br />''A severe heat wave is declared if the maximum temperature crosses the 47-degree Celsius mark.</span><br />