Mumbai smiled as heavy showers lashed the city since midnight and continued till Friday morning, signalling the onset of the monsoon and leaving a minor girl dead. Train services were affected, officials said.Sonali H. Chavan, a resident of Patilari village in Wada, Palghar district died when she was buried under a collapsed wall following heavy rains in the morning.Friday's rain - the first steady downpour after stray unseasonal showers earlier this week - hit the Central Railway suburban section where a signal failure delayed morning peak hour services.Road traffic on both the Eastern Express and Western Express highways as well as other north-south and arterial roads was slowed due to reduced visibility and minor water-logging in some parts of the city.The temperature here dropped to 25.5 degrees Celsius due to the rain, according to the weather department.The weatherman has forecast rain or thundershowers in Mumbai and other coastal areas over the weekend.Monsoon has already set in the coastal Konkan region comprising Sindhudurg, Ratnagiri, Raigad, Thane and Palghar districts with reports of heavy rainfall there.