Chennai, located on the thermal equator along the Bay of Bengal, features a tropical savanna climate characterized by high year-round temperatures and a unique dual-monsoon cycle. Unlike much of India, Chennai receives the bulk of its rainfall during the retreating Northeast monsoon rather than the Southwest monsoon.
Typical Weather Patterns
The city’s weather is defined by three distinct phases: a scorching summer (March to June), a humid transitional monsoon period (July to September), and the primary rainy season followed by a mild winter (October to February). Because of its coastal position, temperatures rarely drop below 20°C (68°F), but the interplay between land heat and sea moisture creates a high heat index that dominates daily life.
Seasonal Trends
- Summer (March – June): This is the most intense period, locally known as Kathiri Veyyil or Agni Nakshatram ("Fiery Star") in May. Temperatures often exceed 38°C (100°F), and when combined with 70%+ humidity, the "feels like" temperature can soar above 45°C (113°F).
- Southwest Monsoon (July – September): While the rest of India experiences heavy rain, Chennai remains relatively dry due to the rain-shadow effect of the Western Ghats. This period is marked by high humidity, overcast skies, and occasional evening thunderstorms that provide brief relief from the heat.
- Northeast Monsoon (October – December): This is Chennai's primary rainy season. It brings heavy, often torrential downpours and is the peak time for tropical cyclones. Over 60% of the annual rainfall occurs now, frequently causing localized flooding in low-lying areas.
- Winter (January – February): The most pleasant time of year. Temperatures range from 20°C to 30°C (68°F–86°F) with lower humidity and clear blue skies. High-pressure systems often bring cool northeasterly breezes.
The Daily Climate Cycle: The Sea Breeze
The most critical daily phenomenon in Chennai is the Sea Breeze. Around mid-morning (usually between 11:30 AM and 1:00 PM), cooler air from the Bay of Bengal begins to move inland.
- The Onset: When the sea breeze sets in, there is a noticeable 2°C–3°C drop in temperature and a corresponding rise in humidity. residents often wait for this "natural air conditioning" to make the outdoors tolerable.
- The Delay: In peak summer, strong westerly winds from the interior can delay the sea breeze until late afternoon, leading to dangerously high temperatures and stagnant, stifling heat in the city center.
Regional Variations and Microclimates
- Coastal vs. Inland: Neighborhoods like Besant Nagar and Marina Beach stay significantly cooler (by 2°C–4°C) due to direct exposure to the sea. Inland areas like Tambaram or Porur experience higher daytime peaks and less immediate relief from the sea breeze.
- Urban Heat Island: Rapid urbanization has led to a "concrete jungle" effect where central districts like T. Nagar trap heat during the day and release it at night, resulting in nighttime temperatures that are 1.5°C higher than historical averages.
Historical Context & Local Adaptation
Historically, Chennai has swung between extreme water scarcity and devastating floods (notably in 2015 and 2023). Locals have adapted by shifting their routines: heavy outdoor activity is traditionally concentrated in the early morning (pre-9:00 AM) or late evening (post-5:00 PM). During the Kathiri Veyyil, it is common for the city to slow down significantly during the "silent hours" of 1:00 PM to 4:00 PM.
What the Weather "Feels Like"
In Chennai, the thermometer is often misleading. Even on a "cool" 30°C day, the high moisture content in the air prevents sweat from evaporating, making it feel "sticky" or "oppressive." Conversely, during the winter months, a slight drop to 22°C combined with the coastal wind can feel surprisingly chilly to locals accustomed to the heat, leading to the rare appearance of light sweaters.