Kolkata: The IMD on Monday said the southwest monsoon is likely to arrive in West Bengal's sub-Himalayan districts like Darjeeling, Kalimpong and Jalpaiguri within the next three to four days.The northern districts of the state are already experiencing pre-monsoon rain with heavy downpour predicted over the next few days.The conditions are favourable for advancement of southwest monsoon into some parts of sub-Himalayan West Bengal within the next three to four days, missing the normal entry date of June 6, the India Meteorological Department said in a bulletin.The weather, however, remained humid in south Bengal despite rain in some places.Also Read: Inflation poses bigger risk than growth this fiscal as monsoon and crude weigh on rural demand: NuvamaHeavy rainfall is likely over the next two days in the sub-Himalayan districts of Darjeeling, Kalimpong, Jalpaiguri, Alipurduar and Cooch Behar, the bulletin stated.It said light to moderate rain is likely to occur in the southern districts of the state during the next two days.Alipurduar, bordering Assam, received the highest amount of rainfall in West Bengal in the past 24 hours till 8.30 am on Monday at 133 mm, the IMD said.Also Read: Heat, humidity of India's monsoon could extend summer heat stress as climate warms: Recent StudyJalpaiguri (53 mm), Cooch Behar (18 mm), Darjeeling (7.8 mm) and Kalimpong (19 mm) received light to moderate rainfall during the period, it said.