MUMBAI, May 27 -- On Monday, the city woke up to a heavy downpour that caught it completely off guard as the India Meteorological Department (IMD) had issued a yellow alert, the second mildest in its colour code, for the day. IMD maintained the yellow alert till 8.30am. It upgraded it to an orange alert at 9.39am. Less than three hours later, at 12.30pm, it further upgraded the warning to a red alert, indicating extreme rains. An official from IMD Mumbai stated that the yellow alert was upgraded to orange after the Colaba observatory logged more than 79 mm of rainfall. However, Akshay Deoras, research scientist at the National Centre for Atmospheric Science, University of Reading, UK, said this was faulty. "Several weather models and satellite images are observed, and based on the wind patterns and rainfall activity expected, the alerts are issued, not after the rainfall is received," he said. "The current winds are approaching from the northwest, and were expected, so an alert of rain could have been declared a day prior. By 12.30 pm, when IMD issued a red alert, most of the weather activity had already passed." Shubhangi Bhute, director of IMD Mumbai was unavailable for comment. On Monday, the weather alerts also coincided with IMD's Regional Meteorological Centre in Mumbai declaring an early onset of the monsoon, the earliest in the last 35 years in Maharashtra and the last 75 years in Mumbai. "The rainy season approaches Mumbai from Kerala, as the southwest monsoon progresses on the west coast. Usually it takes at least 10-15 days for the southwest winds to reach Mumbai-however, this year they have come early," said Sushma Nair, scientist at IMD Mumbai. However, weather experts argued that the doppler radar of IMD showed different synoptic conditions. The scientist said while there were favourable conditions for the monsoon onset, it was not possible for the winds to travel the west coast in two days. Rajesh Kapadia, author of 'Vagaries of Weather', agreed. "The current rainfall activity does not meet IMD's criteria for announcing the monsoon," he said. "There are several technical criteria, which the current patterns do not fulfil. We are currently experiencing winds from the northwest so the rains will pass in two to three days." Deoras highlighted that IMD would have waited to declare the monsoon, had the current rainfall activity not occurred. "For a layperson, the monsoon is generally about the rains, not wind patterns," he said. "However, to avoid criticism from people, IMD declares the monsoon onset closest to a rainfall activity." Both weather experts said the current rain spell would subside over the next two days, leading to dry weather once again. IMD has maintained a yellow alert till Thursday....