West Bengal spans an extraordinary range in a small area — from the Himalayan hill stations of Darjeeling and Kalimpong in the north to the low-lying, cyclone-exposed Sundarbans delta in the south — and is home to the Kalbaisakhi, the severe pre-monsoon thunderstorm squalls unique to eastern India's early-summer weather. For live interactive rainfall, wind and satellite maps over West Bengal, open VayuMet.
The north of the state rises quickly into the Himalayan foothills around Darjeeling and Kalimpong, dropping to the Terai and Dooars plains before flattening into the vast Ganga-Brahmaputra delta that dominates the rest of the state. The southern delta, including the Sundarbans — the world's largest mangrove forest — is low-lying, criss-crossed by tidal rivers, and directly exposed to the Bay of Bengal.
Winter (December-February) is brief and mild. Pre-monsoon summer (March-May) is marked by Kalbaisakhi — sudden, severe thunderstorm squalls with damaging winds and hail. The monsoon (June-September) arrives comparatively early via the Bay of Bengal branch and is the main rain source. Post-monsoon (October-November) is West Bengal's peak cyclone risk window, when the Bay of Bengal is most active.
Intense, fast-developing thunderstorm squalls sweep in from the northwest in late afternoon, bringing damaging winds, hail and lightning — a defining and locally named feature of eastern India's pre-monsoon weather.
The low-lying, densely populated Sundarbans and coastal West Bengal have been struck by major cyclones including Aila (2009) and the supercyclone Amphan (2020), which caused catastrophic damage in and around Kolkata.
Depressions forming in or crossing the Bay of Bengal bring heavy rain spells and occasional river flooding across the Gangetic delta region.
West Bengal, via the Bay of Bengal branch, is typically among the earliest parts of mainland India to receive monsoon rainfall each year.
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 West Bengal's 23 districts, built from IMD's real 1991-2020 gridded rainfall/temperature normals and 1951-2025 daily archives (not a forecast). The Himalayan north and the delta south differ enormously from this average — 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 | 26.0 | 6.6 | 25.5 / 13.2 | 29.1 / 10.8 | 34.3·24.7·0.0 |
| Pre-Monsoon (Summer) Mar–May | 218.0 | 33.2 | 33.4 / 22.3 | 35.1 / 16.8 | 28.8·62.7·0.6 |
| Monsoon (SW) Jun–Sep | 1101.8 | 102.6 | 32.3 / 25.5 | 34.9 / 24.3 | 1.0·88.3·32.7 |
| Post-Monsoon Oct–Dec | 128.1 | 16.9 | 28.4 / 17.8 | 32.5 / 11.1 | 48.8·43.2·0.0 |
State figures are a simple average across 23 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-Nov), also pre-monsoon (May). The Sundarbans and coastal West Bengal are among the most cyclone-exposed regions in India, compounded by low elevation and dense population.
Monsoon (Jun-Sep). The Ganga-Damodar system in the south and Himalaya-fed rivers in the north (Teesta and others) both produce significant, but climatically distinct, flood risk.
Pre-monsoon (Mar-May). Damaging winds, hail and lightning from nor'wester squalls pose a recurring structural and agricultural hazard.
Monsoon (Jun-Sep). The Darjeeling and Kalimpong hills are prone to monsoon-triggered landslides on steep terrain.
Long-term, Sundarbans. The low-lying Sundarbans delta faces a longer-term hazard from sea level rise and increasing salinity intrusion into agricultural land.
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).