Chennai (Madras) weather in September

Regulars call September the better half of a two-month stretch, more pleasant than August though still hot and humid, with the southwest monsoon rain arriving as sporadic few-minute showers rather than the continuous rain of a proper wet month. Our row backs the transitional read - 34.7C reading as a real 40C at 75.5 percent humidity, with 104.5mm across 16.6 days - frequent but each fall brief. The month that actually soaks this coast has not started yet: the northeast monsoon, which brings most of Tamil Nadu's annual rain, sets in around the 20th of October and intensifies from there. The sea is 29.5C. The record: 8.8 hours of sun, a 17.2 kph wind and AQI 66.

Regulars are specific about timing within the month: the northeast monsoon generally sets in around the 20th and intensifies toward month's end, so early October can stay relatively dry while the back third turns genuinely wet, arriving in spells of three to four days followed by roughly a week of calm rather than continuous rain. Our row backs the wet second-half reality, a striking 167.8mm of rain across 18.9 days, alongside intense heat, 33.6C reading as a severe 39C at 80 percent humidity, over 24.9C nights. Regulars call the mornings and evenings genuinely pleasant from here through February, a real improvement over the pre-monsoon months even with the rain risk factored in. The sea holds a warm 30C. The record: 9.2 hours of sun, a 15.1 kph wind and AQI 80.

The north-east monsoon runs from about the 20th of October to the middle of December here, and regulars describe its rhythm rather than its total: two or three days of rain followed by a week or more of nothing. That is how to read our 150.9mm falling across 10.3 days. Opinion splits accordingly - some call December blissful and the best month of the Chennai year, cool by local standards; others report solid rain and suggest January instead. Both are describing the same month from different weeks of it. Heat is moderate for here at 30.3C reading as 33C. The record: 22.3C nights, 9.1 hours of sun, a 27.3C sea and AQI 73.

March is the last month of the Tamil Nadu season and it does not last the whole month. Regulars put the good window at November to March and then qualify it: mid to late March is mostly sunny with highs in the mid to high 30s and lows in the mid 20s, and it starts getting hotter after the middle of the month. Our row's 34.7C average high reads as 39C once the coastal humidity is counted, at 74 percent. Their warning about what follows is blunt - April, May and June are hot and humid enough that people describe struggling to leave the room or the car - and the alternative they recommend for comfort is late November or December. The record: 24C nights, 1.6 precipitation days carrying 7.2mm, 11 hours of sun and a 28.8C sea.

Chennai forum threads consistently name January as one of the more pleasant months to visit, part of a genuinely comfortable October-through-February stretch by the city's own hot-year-round standards, and posters were clear this is real winter here mostly in a relative sense - mornings and evenings noticeably cooler, without daytime rain interrupting plans. Late January was specifically flagged as good weather-wise, coinciding with the Pongal harvest festival around January 14th, when attractions see especially large crowds on the designated outing day, and Mahabalipuram hosts a dance festival around the third week of the month. Posters were consistent that Chennai stays genuinely hot year-round at its core, with January just the gentlest stretch of that heat.