Tamil Nadu is the clearest exception to India's southwest-monsoon-dominated climate: most of the state receives more rain from the northeast monsoon (October-December) than from the southwest monsoon (June-September), because the Western Ghats along its western border block the southwest monsoon while its long Bay of Bengal coastline is fully exposed to the northeast monsoon and its cyclones. For live interactive rainfall, wind and satellite maps over Tamil Nadu, open VayuMet.
The Coromandel coast runs the length of Tamil Nadu's eastern border on the Bay of Bengal, backed by coastal plains and the Cauvery delta, one of India's most important rice-growing regions. The Western Ghats — including the Nilgiris, Anamalai and Palani hills — form the western border and rise over 2,000 m in places; because the state lies on their leeward (eastern) side for the southwest monsoon, most of the interior sees far less rain in that season than the coast does in the northeast monsoon.
Winter (January-February) is mild and mostly dry statewide. Summer (March-May) is hot, especially in the interior plains around Madurai and Tiruchirappalli. The southwest monsoon (June-September) is comparatively weak over most of the state because of the Ghats rain shadow, though the Ghats-facing western fringe (Nilgiris, Coimbatore) still receives meaningful orographic rain. The northeast monsoon (October-December) is Tamil Nadu's principal rainy season, fed by the Bay of Bengal and its depressions and cyclones.
Most of Tamil Nadu's annual rainfall arrives in this window, driven by the northeast monsoon current and the depressions and cyclones that regularly form in or cross the Bay of Bengal at this time of year.
The Tamil Nadu coast, particularly around Chennai, Cuddalore and Nagapattinam, sees direct cyclone landfall or close-passage impact from the Bay of Bengal on a fairly regular multi-year basis.
Because the Western Ghats block most southwest monsoon moisture, this season is comparatively dry for most of Tamil Nadu except the immediate Ghats-facing western districts.
Pre-monsoon heating produces scattered but sometimes intense thunderstorm activity across the interior plains.
Frequencies cited from published IMD/IITM climatology where a source is named inline; day-count figures in the table below are computed directly from the 1951–2025 IMD daily archive.
The table below is a state-wide average across Tamil Nadu's 38 districts, built from IMD's real 1991-2020 gridded rainfall/temperature normals and 1951-2025 daily archives (not a forecast). The Nilgiris and other Ghats-facing districts differ substantially from this average, as do the northeast-monsoon-heavy coastal districts — use the district climatology tool linked below for any single district's own figures.
| Season | Rainfall (mm) | Rain days | Mean Max / Min (°C) | Typical Hottest / Coldest (°C) | Sky (Sunny·Partly·Overcast days) |
|---|---|---|---|---|---|
| Winter Jan–Feb | 23.0 | 5.5 | 30.3 / 20.6 | 32.3 / 19.7 | 10.4·47.7·0.9 |
| Pre-Monsoon (Summer) Mar–May | 139.2 | 21.9 | 34.6 / 24.6 | 36.2 / 21.6 | 11.6·75.6·4.8 |
| Monsoon (SW) Jun–Sep | 396.4 | 57.0 | 33.1 / 24.5 | 35.3 / 23.6 | 0.0·54.9·67.1 |
| Post-Monsoon Oct–Dec | 502.9 | 46.3 | 29.6 / 22.1 | 32.0 / 19.8 | 3.0·78.4·10.6 |
State figures are a simple average across 38 member districts (IMD Pune 1991–2020 normal; day-count and sky figures from real 1951–2025 daily archives — see District Climatology tool for any single district's own numbers, which can differ substantially from this state average).
Computed directly from the real IMD 1951–2025 daily gridded archive — not a forecast, and not the same as a single-station record. IMD's gridded temperature is 1°×1° (~111 km/cell) and rainfall is 0.25°×0.25° (~25 km/cell); both are spatial analyses of many station observations; a famous single-station record (e.g. a specific town's all-time hottest day) will typically read higher than the grid-cell value shown here, since one station reading isn't smoothed over a ~25–111 km box. "Place" is the nearest district to the grid cell where the extreme occurred, not necessarily the exact spot.
Post-monsoon (Oct-Dec), also pre-monsoon. Coastal districts from Chennai to the far south face recurring cyclone landfall or close-passage risk from the Bay of Bengal.
Northeast monsoon (Oct-Dec). Intense northeast monsoon rainfall has caused severe urban flooding in Chennai (notably 2015) and river flooding along the Cauvery, Vaigai and other systems.
Monsoon-shortfall years. The interior plains, especially the Cauvery-dependent delta and upstream districts, are vulnerable to drought in years both monsoons underperform, with added strain from interstate river-water disputes.
Summer (Mar-May). Interior districts such as Madurai, Tiruchirappalli and Vellore see periodic heatwave conditions ahead of the weak southwest monsoon.
Click a district on the District Climatology tool or search it on the 10-day forecast page for its own normals — the grid below is the full current list (India's Local Government Directory codes, cross-checked against the latest state reorganisation).