IMD Monsoon Prediction System (Geography)
IMD Monsoon Prediction System(Geography)
Why In News:
The India Meteorological Department (IMD) confirmed the onset of the Southwest (SW) Monsoon over Kerala on 4 June 2026.
Monsoon Prediction System:
Statistical model + Dynamical Global Forecast System (GFS) are used by IMD for monsoon prediction.
IMD issues a Long Range Forecast (LRF) in April (Stage 1) and May (Stage 2) every year.
Monsoon onset is declared when: (i) Rainfall is ≥2.5 mm/day for 2 consecutive days; (ii) Outgoing Longwave Radiation (OLR) is <200 W/m²; (iii) Wind speed and direction criteria are met.
Key Facts for Prelims:
El Niño — warming of the Central-Pacific sea surface — is typically associated with a deficient/below-normal monsoon in India.
La Niña — cooling of Central-Pacific — generally associated with above-normal monsoon.
Indian Ocean Dipole (IOD): A positive IOD (warmer western Indian Ocean) can partially offset El Niño effects, boosting the monsoon.
Mascarene High: A high-pressure system near the Mascarene Islands in the southern Indian Ocean; acts as the 'engine' driving SW Monsoon winds northward.
India's NW states (Rajasthan, Gujarat) are last to receive SW Monsoon — typically by mid-July.
Northeast Monsoon (Retreating Monsoon): Brings rainfall to Tamil Nadu, Andhra Pradesh, and Sri Lanka during Oct–Dec as the SW monsoon retreats.