West Bengal spans from the Bay of Bengal coast and Sundarbans delta to the sub-Himalayan foothills (Darjeeling, Kalimpong) — rainfall varies from 1,400 mm in the south to 3,500+ mm in the north. The Bay of Bengal branch is less suppressed by El Niño than the Arabian Sea branch, supporting a near-normal 2026 outlook. For live maps, open VayuMet.
| District / City | Day 1–2 (mm) | Day 3–4 (mm) | Day 5–7 (mm) | Confidence |
|---|---|---|---|---|
| Kolkata | 8–25 | 15–40 | 25–65 | Moderate |
| Siliguri (Darjeeling) | 15–40 | 30–75 | 50–120 | Low–Moderate |
| Asansol (Paschim Bardhaman) | 5–18 | 10–30 | 18–50 | Moderate |
| Bardhaman | 5–20 | 12–35 | 20–55 | Moderate |
| Malda | 8–25 | 15–40 | 25–65 | Moderate |
| Cooch Behar | 10–30 | 20–55 | 35–90 | Low–Moderate |
| Sundarbans (South 24 Parganas) | 8–22 | 15–38 | 22–58 | Moderate |
| Midnapore (Paschim) | 5–18 | 12–32 | 20–50 | Moderate |
Note: GFS significantly underestimates sub-Himalayan rainfall over Darjeeling, Kalimpong, and Jalpaiguri due to steep orographic gradients. Actual observed rainfall in the hills can be 2–3× GFS values during active monsoon.
The sub-Himalayan districts receive some of India's highest rainfall — Darjeeling averages ~3,000 mm and Jalpaiguri ~3,500 mm annually. The monsoon arrives early, around 5–8 June, and is driven by orographic uplift over the Himalayan foothills. This zone is least El Niño-sensitive in WB — 2026 outlook is near-normal to above-normal for sub-Himalayan WB.
The Gangetic plains of WB receive onset around 8–12 June and average 1,400–1,600 mm annually. Bay of Bengal depressions are the key rainfall drivers — these form frequently in the monsoon season and track northwest across Odisha and WB. The BoB branch is relatively less suppressed by El Niño — WB's 2026 outlook is near-normal.
The Sundarbans mangrove delta is one of the world's most cyclone-vulnerable regions — Cyclone Amphan (2020, Super Cyclonic Storm) and Yaas (2021) caused catastrophic storm surge damage. The monsoon onset here is also among India's earliest at ~8 June. Flooding from both river discharge and storm surge is a compounding hazard.