The best time to visit is the cool, dry winter from November to February, with pleasant days around 20 to 30 degrees ideal for sightseeing. March to May grows hot and very humid, and the southwest monsoon from June to September brings heavy rain and occasional flooding that can snarl traffic and trains, though the green, storm-washed city has its own dramatic appeal.
During the monsoon from June to September, heavy downpours can flood low-lying roads and railway tracks within hours, stranding traffic and suspending local trains. Check the forecast, avoid underpasses in heavy rain, allow extra time, and keep some cash and a charged phone for disruptions.
Mumbai is dense and its traffic is relentless, with informal crossings and bikes weaving through gaps, so cross with locals and stay alert. Petty theft and pickpocketing occur in crowds, on packed trains and around tourist sights, so keep bags zipped and in front and phones secure.
Street food is a highlight but can upset an unaccustomed stomach, so choose busy stalls with fresh, hot, high-turnover food and build up gradually. Drink bottled or filtered water, skip ice and raw salads if unsure, and carry basic stomach remedies and hand sanitiser.