Kerala is the gateway of the Indian monsoon. India's southwest monsoon makes its first landfall over Kerala's Western Ghats coast, normally on 1 June (±7 days). IMD's official 2026 forecast: ~26 May — approximately five days early. However, IMD's April 2026 Long-Range Forecast projects below-normal seasonal rainfall at 92% of LPA nationally — early onset does not guarantee a good season.
| District / City | Day 1–2 (mm) | Day 3–4 (mm) | Day 5–7 (mm) | Confidence |
|---|---|---|---|---|
| Thiruvananthapuram | 5–15 | 10–30 | 15–45 | Moderate |
| Kollam | 5–18 | 12–35 | 15–50 | Moderate |
| Alappuzha | 4–14 | 10–30 | 15–40 | Moderate |
| Kottayam | 5–20 | 12–35 | 20–55 | Moderate |
| Ernakulam (Kochi) | 5–18 | 10–30 | 15–45 | Moderate |
| Idukki | 10–30 | 20–55 | 30–80 | Low–Moderate |
| Thrissur | 4–15 | 10–28 | 15–40 | Moderate |
| Palakkad | 2–8 | 5–15 | 8–25 | Moderate |
| Kozhikode (Calicut) | 5–20 | 15–40 | 20–55 | Moderate |
| Malappuram | 4–15 | 10–30 | 15–45 | Moderate |
| Wayanad | 10–30 | 20–55 | 30–75 | Low–Moderate |
| Kannur | 5–20 | 15–40 | 20–55 | Moderate |
| Kasaragod | 5–18 | 12–35 | 15–45 | Moderate |
| Pathanamthitta | 5–20 | 12–35 | 20–55 | Moderate |
Note: GFS at 0.25° significantly underestimates orographic rainfall over the Western Ghats. Idukki and Wayanad can receive 2–4× the GFS-indicated values during active monsoon. Use VayuMet maps for spatial pattern guidance, not point-precise values.
The normal southwest monsoon onset over Kerala is 1 June, with a standard deviation of about ±7 days. Onset is declared by IMD when the low-level westerly jet strengthens over the Arabian Sea, cloudiness deepens, and widespread rainfall stations in southern Kerala report ≥2.5 mm on two consecutive days.
IMD's official 2026 forecast (issued April 2026) places Kerala onset at ~26 May — approximately five days ahead of the climatological normal. A Bay of Bengal low-pressure system in mid-May 2026 accelerated the northward advance of the ITCZ, priming the onset earlier than usual. The ±4-day uncertainty range means the actual onset could fall between 22–30 May.
Despite the early onset, IMD's April 2026 Long-Range Forecast projects below-normal seasonal (JJAS) rainfall at 92% of LPA for the country as a whole, with a 35% probability of deficient rainfall. An El Niño event is developing (98% probability, NOAA/IRI), which historically suppresses rainfall over south and central India during June–August. Kerala's high-elevation districts (Idukki, Wayanad) benefit from orographic enhancement and may see near-normal totals even in weak national seasons, but the broader Kerala coastal outlook leans below-normal. Refer to the India Monsoon 2026 article for the full state-by-state breakdown.