The ongoing heat wave overseen by a trans-Pacific ‘ridge' (high-pressure region) is a ‘sacrifice' that central and north-west India would need to put up with in the short-term if only to ensure longer-term ‘gains.'
There is no one-to-one relationship with this sacrifice (abnormal heat) and the expected gains (from a monsoon later), says Dr Akhilesh Gupta, leading operational forecaster and Advisor, Department of Science and Technology.
Major enabler
But the heating is a crucial enabler of the temperature gradient (monsoon is derived from the differential heating of sea and land) - which, in turn, sets up the pressure gradient (high in the south to low in the northwest) for rains to canter into the rest of the mainland.
Western disturbance activity and their cooling impact, can, however, interfere with the heating process, and are generally wished away during the pre-monsoon season.
The westerly activity has been subdued over the last week or so, which has helped the accelerated heating of west and north-west India as well. The hot-air spewing ridge is forecast to hold strong during the next week.
The India Meteorological Department (IMD) has indicated the possibility of a feeble western disturbance entering the north-west around Sunday causing rains over Jammu and Kashmir and Himachal Pradesh.
IMD has also held out the possibility of the rains filtering into the adjoining plains, but is not supported by the outlook by international weather models. If the plains were to get rains as forecast by the IMD, the heating process would get impacted.
US forecasts
In fact, the Global Forecast System (GFS) model of the US National Oceanic and Atmospheric Administration (NOAA) does not see any respite from the heat wave for the north-west, except over Jammu and Kashmir and adjoining extreme north India.
This model sees temperature regime of above 40 deg Celsius growing its footprint over the northern three-fourths of the country next week. The top heat is forecast to gradually envelop the southeast peninsula as well (including interior and coastal Tamil Nadu).
The only respite would be brought about by the occasional thundershowers that are forecast to break out around the seasonal trough that will constantly shift its alignment within the larger eastern corridor.
Westerly flows would just add to the volatility by supplying moisture and keeping the trough to the east of the country ‘on the boil.' In fact, thunderstorms over northeast India are forecast to get a fresh lease of life in this manner, during the next week.
On Friday, such a trough ran down from Bihar south-southwest to Lakshadweep area across east Madhya Pradesh, Vidarbha, Telangana and Kerala and featured an embedded cyclonic circulation over Lakshadweep.
A warning issued by the IMD on Friday said that heat wave conditions may continue to hold over Rajasthan, interior Gujarat, north Madhya Pradesh, Chhattisgarh and Vidarbha during the next 24 hours.
Severe heat wave conditions existed over parts of Rajasthan, Gujarat, west Madhya Pradesh, Himachal Pradesh, Uttarakhand and isolated pockets of Chhattisgarh, west Uttar Pradesh and Vidarbha.
Maximum temperatures were above normal by 4 to 7 deg Celsius over many parts of northwest and central India, interior Orissa and Gujarat. The highest maximum temperature of 44.7 deg Celsius was recorded at Akola and Brahmapuri in Maharashtra.
Satellite imagery showed the presence of convective clouds over parts of south Arabian Sea and south Bay of Bengal. Low to medium clouds were traced over northwest, central and peninsular India and the North-Eastern States.
Satellite pictures also showed the entire western India covered by a large sweep of high clouds but apparently no calming influence on ground level temperatures.
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