Mumbai: The city witnessed an exceptionally wet May this year, with south Mumbai recording its highest rainfall for the month in over a century.While the IMD’s Colaba observatory broke the all-time rainfall record for May by logging 503 mm — surpassing the previous record of 279.4 mm set in May 1918 — area-specific data from the city’s automatic weather stations paints a more detailed picture. Nariman Point recorded 499.7 mm of rainfall, followed by Grant Road (491 mm), Reay Road (457 mm), Colaba (449 mm), and Marine Lines (444 mm). In contrast, suburban areas such as Mulund (146 mm), Trombay (165 mm), Malad (154 mm), Bhandup (154 mm), and Borivli (177 mm) received less than half these amounts.Independent weather enthusiasts attribute the extreme May rainfall to the remnants of a depression from the Arabian Sea (see graphic). “A lot of the spatial variations had to do with the wind direction and the landfall location of the depression. The northerly component to the winds helped keep most of the heavy rain towards (the southern Mumbai region). Instead of crossing over at Ratnagiri, had it crossed over in Raigad, the area of influence and convergence zone would have been more northwards,” said Athreya Shetty, a weather enthusiast.Shetty said that in the monsoon, the offshore trough and strength of westerly winds dictates rainfall distribution. “If the offshore trough is active towards northern MMR, then the suburbs, Thane, Navi Mumbai and Palghar will bear the brunt of heavy rain driven in by strong westerlies. In such cases the island city scores less, being a thin strip of land. But in a few instances, the offshore trough is active only till north Raigad, in which case intense rain bands tend to form near the Alibaug-Uran side, leading to the island city scoring more than the suburbs,” he explained.Meanwhile, IMD has issued a yellow alert for Mumbai, Thane and Raigad, indicating thunderstorms accompanied with lightning for Thursday.