MUMBAI: The IMD has issued an orange alert for Mumbai, Thane , and Palghar for Sept 25, Wednesday, indicating heavy to very heavy rainfall and thunderstorms with lightning and gusty winds at isolated places being very likely. For Raigad, meanwhile, a red alert has been issued for Sept 25 itself, forecasting extremely heavy rainfall and thunderstorms with lightning and gusty winds at isolated places. Meanwhile, in the early hours of Tuesday, Mumbai recorded its first heavy rain spell for the month of September.

In the 24 hours ending at 8.30am on Sept 24, the IMD Santacruz observatory recorded 75 mm of rain. According to IMD classification, rainfall recorded between 64.

5mm-115.5mm falls in the heavy rain category. An IMD official explained that all the heavy rains recorded were between 2.

30 am-4.30 am on Tuesday; however, this may increase on Wednesday night. "There was thunderstorm activity accompanied by lightning owing to the existing weather conditions, which are very conducive for thunder activity," said the official.

Some city residents said that heavy rains and loud thunder woke them up suddenly. "It started around 3 am and was accompanied by short and heavy spells," said a resident. Adjoining area residents like Kalyan, Dombivli, Thane, and Panvel also experienced similar weather activity.

Thunderstorm activity is mostly restricted to certain areas only and is also a feature of the retreating monsoon. The southwest monsoon has already begun its withdrawal, and on Tuesd.