IMD scientist explains why Bengaluru faces strong Aashada winds in July

Strong, gusty winds known locally as 'Aashada gaali' have swept across Bengaluru this July, bringing persistent cloudy weather and wind speeds of approximately 35 kilometres per hour to the city. Latha Sridhar, a scientist at the India Meteorological Department (IMD) in Bengaluru, explained that the weather pattern is caused by the strengthening of southwesterly monsoon winds over the Indian peninsula.

According to Sridhar, 'Aashada gaali' is not a separate meteorological phenomenon but has been recognised in local weather lore for centuries. The traditional term refers to the characteristic strong, persistent winds of the Hindu month of Aashada, which roughly coincides with July. Sridhar highlighted a traditional Kannada saying, "Aashada gaalige aane kocchi hoyitu," which translates to "even elephants are swept away" during these winds.

The scientific explanation behind the winds lies in the prevailing South Westerlies that bring monsoon rains to Karnataka. Sridhar explained that a strong pressure gradient is established during this period, featuring high pressure over the southern Indian Ocean and low pressure over northwest India and Pakistan. This causes an intensified flow of moisture-laden air from the Arabian Sea towards the west coast and the interior regions of Karnataka.

These winds are part of a low jet stream, also known as the Somali Jet or Findlater Jet. This jet stream forms between 1 and 1.5 kilometres above sea level, which is much lower than other high-altitude jet streams like the Subtropical Westerly Jet or the Tropical Easterly Jet. The winds travel at high speeds of 37 to 74 kilometres per hour over the Arabian Sea, maintaining similar or slightly reduced speeds as they flow through the gaps and terrain of the Western Ghats before reaching Bengaluru.

Unlike short-lived thunderstorm winds that typically dissipate within half an hour, the Aashada winds are continuous. They are accompanied by intensive cloud cover that persists over days or weeks.

The weather pattern has different impacts across the region. In agrarian communities, farmers associate these winds with good soil moisture and view it as the season to sow kharif crops. Conversely, in coastal areas, the winds cause very rough sea conditions, impacting local fishermen.