Kolkata: The southwest monsoon set over Kerala on Saturday, eight days ahead of its normal arrival date, bringing hope for the monsoon rain to reach Kolkata. The Met officials, however, said early onset in Kerala did not guarantee its advanced arrival in Kolkata and the rest of Bengal.

Even though a 10-day gap between Kerala and south Bengal onset is considered normal, meteorologists said there were various factors to influence the monsoon's arms touching down here.Under normal conditions, the monsoon should keep its date with the city by June 11, with an error margin of plus or minus four days. In the past 15 years, it arrived on time only on four occasions. In 2024, it hit Kolkata on June 21, 22 days after Kerala.

The gap between Kerala and south Bengal onset has varied between eight and 25 days in the past one and a half decades."Early monsoon onset in Kerala doesn't always translate into early onset in Bengal. There are several dynamic factors we have to consider for the advancement of the SW monsoon over our region, like the strength of monsoon flow and other systems over the Bay of Bengal," said meteorologist HR Biswas, head of weather forecast section at RMC Kolkata.

RMC officials said monsoon arrived in Kerala with a bang, causing heavy rain, and its flow was likely to be active and strong for at least the next one or two days. But despite starting on a dashing note, the monsoon flow often gets into a sluggish phase, refusing to extend its arms further for days. That is how it took 22 days for it to reach Kolkata last year after its arrival in Kerala.The Met officials are, however, pinning hope on a low-pressure area likely to develop over the west-central and adjoining north Bay of Bengal by Wednesday, as this system can influence the SW monsoon's advancement towards Kolkata.

"The position of this likely system, its movement, and intensity will also have a bearing on the monsoon's arrival in south Bengal," added Biswas.While the low-pressure area is expected to trigger widespread pre-monsoon showers from Thursday in Kolkata and other districts, until then, the city can expect light rain. A partly cloudy sky and scattered rain measuring 1.6 mm ensured both the maximum and minimum temperatures remained below the normal mark at 32.6 and 25.8 Celsius, respectively, on Saturday.