Abstract Accelerated land transformation may exacerbate urban heat, however coastal municipalities can benefit from sea-breeze cooling, elevated humidity, and pronounced diurnal temperature variations. This research integrates documented remote-sensing metrics for Mumbai, Kolkata, and Chennai from 2001/2003 to 2023 to assess urban land-cover changes, daily cooling patterns, core-periphery temperature variations, and humid heat. The Centre for Science and Environment's 2024 evaluation obtained source metrics from MODIS land-surface temperature and Landsat land-use/vegetation datasets; this study independently recalculated alterations, rates, and precise small-sample statistics. The accumulated proportion rose throughout all urban areas, from an average of 46.37% in three cities to 68.57%, but the average green share declined from 28.33% to 21.67%. Chennai had the most rapid transformation, with the built-up area increasing by 42.8 percentage points and the green area decreasing by 13.7 points. In 2023, Kolkata retained its status as the most developed city with an 80.1% built-up area. Urban centers at night were warmer than their outskirts in Mumbai (+0.4°C), Kolkata (+1.2°C), and Chennai (+0.9°C), despite Mumbai's core being 3.5°C colder during the day. Documented daily cooling decreased by 24% in Mumbai and 5% in Chennai; the associated reconstructed cooling values from previous periods were 10.26°C and 10.21°C, respectively. Increased humidity contributed an estimated 5.0–6.6°C to perceived heat stress. The limited number of three cities rendered paired and exact permutation tests ineffective; the robust descriptive correlation between the ultimate built-up share and nighttime core heat (r = 0.988) lacked conventional significance. The results indicate that coastal urban heat is a multifaceted, temporally variable occurrence. Planning must emphasise nighttime thermal retention, uninterrupted blue-green infrastructures, cool materials, ventilation pathways, and humidity-sensitive heat management technologies.