Vinson Kurian
Thiruvananthapuram, Feb. 8 Northwest India is expecting a fresh western disturbance to impact regional weather for three days from Monday over the hilly region and two days from Tuesday over the plains.
Minimum temperatures have inched up above normal by 2-4 deg Celsius C over parts of Uttarkhand, southeast Rajasthan, west Madhya Pradesh, south Chhattisgarh, Madhya Maharashtra and interior Karnataka in anticipation.
The US-based Centre for Ocean-Land-Atmospheric Studies (COLA) estimates that the mean mercury level would range between 15 and 20 deg Celsius over northwest and central India, and between 25 and 30 deg Celsius over north peninsula during this week. The south peninsula would be comparatively cooler at 20-25 deg Celsius.
The mercury level is expected to come down over northwest and central India during the week starting February 16 presumably following the exit of an intervening western disturbance.
MOISTURE SWEEP International model predictions suggest that a trough in the westerlies would dip down into central India during the next three days and sweep some moisture from the Arabian Sea into the mainland.
Some of these models predicted a narrow streak of moisture arching in a southwest-to-northeast direction from the west coast to straddle the peninsula before heading into the Head Bay of Bengal and later into northeast India. This may cause the humidity levels to rise along this narrow corridor.
India Meteorological Department quoted weather prediction models to suggest that minimum temperatures would fall by 1-2 deg Celsius during the next 24 hours but rise by 2-4 deg Celsius from Thursday onwards over northwest and adjoining central India.
Rain or snow is likely at a few places over Jammu and Kashmir and Himachal Pradesh from Monday onwards. Isolated to scattered rain or snow is likely over the western Himalayan region until Thursday.
The westerlies associated with the system are shown to take the sails away from tropical moisture surge from the east Indian Ocean/southeast Bay of Bengal causing it to die out immediately after impacting Sri Lanka during this week.
WAIT FOR RAINS This would mean that the south extreme peninsula would have to sit out the week to get some anticipated showers, according to COLA.
Sea surface temperatures in the Bay of Bengal continue to be below the threshold level for sparking sustained convection and precipitation, as per the US Naval Coupled Ocean Data Assimilation charts.
Contrastingly, the Arabian Sea is warmer for the most part, which prompts some models to throw up occasional troughs of low pressure along the west coast but largely lacking the depth to trigger precipitation.
The Climate Prediction Centre of the US National Weather Services sees the Inter Tropical Convergence Zone (ITCZ), or the global band of low-pressure that tracks the position of the Sun, toying with the southeast Sri Lanka coast.
The ITCZ, home to constant thunderstorms and precipitation, is currently active to the south of the Equator mainly over the south Pacific and south Indian Ocean. For this reason, it is also called the South Pacific Convergence Zone (SPCZ).
The SPCZ is driving the Australian monsoon and dumping rains over the Maritime continent (group of peninsular or island nations in the Pacific that includes Malaysia, Indonesia and the Philippines).