The Southwest Monsoon officially arrived in Kerala on Thursday, a few days after the India Meteorological Department (IMD) had forecast its arrival. The onset was delayed by around three days compared to its normal arrival date.After making landfall in Kerala, the monsoon typically progresses northward in phases, covering most parts of the country by mid-July.After making landfall in Kerala, the monsoon typically progresses northward in phases, covering most parts of the country by mid-July.Its arrival is closely watched because of its importance to India's agriculture-dependent economy. According to agriculture ministry, nearly 51% of the country's cultivated land relies on rainfall, contributing about 40% of agricultural production. With almost half of India's population dependent on farming for their livelihood, a healthy monsoon season is considered crucial for rural incomes and overall economic activity.Also read | Monsoon likely to arrive in Kerala three days behind schedule around Jun 4: IMDEarlier, the IMD had said conditions were becoming favourable for the monsoon to advance into additional areas of the Arabian Sea, Bay of Bengal, Lakshadweep, Kerala, Tamil Nadu and adjoining regions.Heavy rainfall across KeralaThe weather agency has also forecast isolated heavy to very heavy rainfall across Kerala over the next several days, while parts of Tamil Nadu and Karnataka are expected to receive heavy showers. Also read | 80% chance of El Nino forming between June and August, warns World Meteorological OrganisationThunderstorms accompanied by strong winds are also likely over several regions of north-west, central, eastern and southern India.Meteorologists had linked the delayed onset to a developing typhoon over the western Pacific, which drew moisture away from the Arabian Sea and Bay of Bengal, along with a cyclonic circulation near the Lakshadweep region. These factors are believed to have slowed the monsoon's progress and weakened its initial advance into Kerala.80% chance of El Nino forming between June and AugustIn India, an El Nino is associated with a weaker monsoon and harsher summer.The El Nino which is currently taking shape will be moderate and could even be strong, said the update, a possibility that will raise alarm bells in India, which is already staring at a weak monsoon.The possibility that El Nino conditions will develop until at least November is “near or above 90%”, said the agency.(With inputs from Jayashree Nandi)