Being the state's most populous district and criss-crossed by rivers and canals, humidity stays high here all year round. Nor'westers (March–May) strike this district first as storms move up from the south, so keeping an eye on thunderstorm forecasts matters.
Usually between March and May, in the afternoon or evening. During this window, watch the live card for the day's rain chance and wind speed.
Not fundamentally, but the southern belt toward the Sundarbans is more humid, and this district usually sees the first rain when a Bay of Bengal low pressure forms.
If a storm is forecast, avoid standing in open fields or under trees, and unplug electronic appliances from the power supply.