A September 24 view from India’s INSAT-3DS weather satellite captured a pronounced divide in the country’s weather conditions, with extensive cloud systems covering central, eastern and southern regions while large parts of northwest India appeared comparatively clear, as per a NBT report. The image, recorded in the thermal-infrared channel at 10.83 micrometres, provides a snapshot of the contrasting atmospheric conditions prevailing across India as the southwest monsoon entered its closing phase.
The pattern was linked to an active weather system over the eastern side of the country, where moisture was spreading inland from the Bay of Bengal. At the same time, drier conditions were becoming more evident across parts of the northwest. The India Meteorological Department had reported a deep depression over north coastal Andhra Pradesh and adjoining south Odisha during this period, with the system moving inland and continuing to influence rainfall across central and eastern India.
Cloud bands stretch from central India into the east
The satellite view showed a large concentration of clouds extending across central India and towards the east and northeast. Additional dense cloud cover could be seen over the Bay of Bengal and areas surrounding the eastern coast, highlighting the flow of moisture from the sea towards the mainland.
The contrast with northwestern India was visible from space. Parts of Rajasthan and Gujarat, along with several neighbouring areas, appeared substantially less cloudy. The difference reflected the separate weather influences affecting the two broad regions when INSAT-3DS captured the image.
Rather than marking a permanent divide between rainy and dry parts of India, the satellite picture records where clouds and convective activity were concentrated at that particular time.
Why the brightest patches indicate colder cloud tops
Because the INSAT-3DS image uses thermal-infrared observations, the brightness of the clouds provides information about their temperature. Areas appearing brighter generally represent colder cloud tops, which are often found higher in the atmosphere.
Tall, cold cloud formations can be associated with deep convection. When such clouds develop around an active weather system, they can produce intense showers, thunderstorms and episodes of very heavy rainfall.
Infrared observations are particularly useful to weather forecasters because they allow large cloud systems to be monitored over broad areas, including locations where observations from the ground may be more limited.
Deep depression spreads moisture beyond the east coast
The contrasting satellite pattern developed as a deep depression that had been positioned over north coastal Andhra Pradesh and adjoining south Odisha moved inland. The system had already produced widespread rainfall across Odisha, Chhattisgarh and nearby areas.
The IMD had forecast heavy to very heavy rainfall, including isolated extremely heavy rainfall in parts of central and eastern India. As the system travelled northwestwards and weakened gradually, its circulation continued to draw and transport moisture over land, helping sustain cloud formation farther from the original coastal area.
This explains why the cloud field visible in the satellite image extended deep into central India instead of remaining concentrated around the east coast.
Bay of Bengal remains a major moisture source
The Bay of Bengal was another prominent part of the satellite picture, with extensive clouds visible over the water and extending towards the mainland.
The bay can supply large amounts of moisture to monsoon weather systems. When a depression or low-pressure system develops, moisture from the surrounding ocean can be pulled towards land, supporting cloud development and rainfall.
The September 24 image captured that process, showing bands of cloud stretching from the moisture-rich Bay of Bengal towards parts of central and eastern India.
Why northwest India appears comparatively cloud-free
The relatively open skies over much of northwest India also fit the seasonal transition taking place in late September. The southwest monsoon generally begins withdrawing from northwest India around this time, although the precise timing and progression can vary each year.
As the monsoon retreats, atmospheric conditions over parts of the northwest can become drier, reducing the development of large cloud systems. Meanwhile, weather systems originating or strengthening over the Bay of Bengal can continue to deliver rainfall farther east and south.
This means the transition away from the monsoon does not occur uniformly across the country. While one region can begin moving towards drier conditions, another can remain under the influence of a moisture-rich weather system.
One satellite image captures two seasonal patterns
The INSAT-3DS observation illustrates how different phases of the monsoon transition can exist across India at the same time. The clearer northwest reflected the gradual shift towards drier conditions, while the widespread cloud cover farther east and south showed the continuing influence of an active weather system and moisture from the Bay of Bengal.
Such a pattern can change rapidly as weather systems move and weaken. For meteorologists, satellite observations provide a continuous way to track those shifts, monitor cloud development and follow weather systems across a country where atmospheric conditions can vary sharply over relatively short distances.
