Wednesday, September 16, 2020

MONSOON WITHDRAWAL DELAYED?

 

v  Current weather phenomenon

The monsoon trough lies to the south of its normal position. Its eastern end is very likely to remain to the south of its normal position till 17th September, 2020. An east-west shear zone runs roughly along Latitude 15°N between 3.1 & 5.8 km above mean sea level. It is likely to persist during next 2 days.



v  No indication as yet of monsoon withdrawal from north-west India. Another low-pressure area is likely to develop over the Bay of Bengal around September 17; monsoon forecast need to be assessing further to be certain. Monsoon withdrawal can begin only once anti-cyclonic flow is established and moisture reduces significantly over the region.  

v  The Southwest monsoon stuck deviating significantly from the geographic distribution

Normally, the withdrawal of monsoon is supposed to begin from September 17 when rains begin to reduce across the country until completely withdrawing on October 15. But this year monsoon range extended, forecast shows extensive and heavy rains along the west coast between September 11 and 24 and then until October 1 over several parts of central India.

v  Monsoon overall scenario

The month of June started on the extremely wet note and finished with a surplus of 18%, the best performance in the last 7 years. Peninsular India has recorded 26.3% excess rain this monsoon since June 1 and 78.6% excess rain in September (till September 14). It is expecting more rain due to a well-marked low-pressure area that has developed over the Bay of Bengal. Northwest India has seen 13.5% lower rainfall since June 1.  However, there are parts within this region that have done worse. 

west Uttar Pradesh has seen 30% lower rains; Himachal Pradesh, 18% lower; Uttarakhand, 15% lower; Jammu and Kashmir 27% lower; and Haryana, Chandigarh and Delhi, 6% lower. Rainfall that is between -20% and -59% of the average is termed deficient. West Rajasthan, also in the same region has seen a 30% surplus. North-western region is unlikely to record heavy rain between now and the end of the monsoon. The month of June, July, and August put together have a normal rainfall of 710.5mm (June 166.9 mm, July 285.3 mm, and August 258.3 mm). September holds the key to the overall seasonal performance.

This monsoon has been characterized by several unique features , such as no low-pressure areas forming in July, resulting in the monsoon trough (line of low pressure) oscillating to the Himalayan foothills very frequently bringing rains mainly to the peninsular region and northeast India in July while leaving northwest India dry. Five low pressure systems formed in August which brought excess rains to the central and western region but not much to the north-western region again. Even in this scenario, the Monsoon 2020 is heading towards ‘Above Normal’ status with an outside chance to repeat the performance of 2019 and reach near 110%.

 

v  Five days nationwide forecast

Due to the current existence weather conditions extensive rain in the North East due to the hot & humid southwesterly winds will continue until Thursday.  Rain areas due to low pressure and the monsoon trough will be limited to Maharashtra also the Malabar Coast & southern part of the Konkan Coast, respectively. In addition, heavy rains are possible over the Malabar Coast & southern part of the Konkan Coast on Saturday.
  

16 September (Day 1): Heavy to very heavy rainfall very likely at isolated places over Madhya Maharashtra and North-east India. heavy rainfall at isolated places over southwest Madhya Pradesh, Bihar, Coastal Andhra Pradesh, Telangana, Coastal & North Interior Karnataka, Kerala, and Tamilnadu. Thunderstorm accompanied with lightning likely at isolated places over East Uttar Pradesh and isolated places of Madhya Pradesh.

 

17 September (Day 2): Heavy rainfall likely at isolated places over southwest Madhya Pradesh, Bihar, Madhya Maharashtra and thunderstorm accompanied with lightning expected at isolated places over East Uttar Pradesh Rajasthan, Madhya Pradesh.




18 September (Day 3):  Heavy to very heavy rainfall likely at isolated places over Coastal Karnataka and Kerala. Heavy rainfall at isolated places over southeast Rajasthan, southwest Madhya Pradesh, North-eastern states Gujarat State, Madhya Maharashtra,Coastal Andhra Pradesh, Telangana and Interior Karnataka. Thunderstorm accompanied with lightning likely at isolated places over East Uttar Pradesh, Rajasthan, West Madhya Pradesh, Jharkhand and Odisha.

 


19 September (Day 4):  Heavy to very heavy rainfall likely at isolated places Coastal Karnataka and, Kerala and heavy rainfall at isolated places over southeast Rajasthan, West Madhya Pradesh, Odisha, northeast India, Andhra Pradesh and Interior Karnataka. Thunderstorm accompanied with lightning likely at isolated places over East Uttar Pradesh, East Rajasthan, West Madhya Pradesh, Jharkhand, Odisha and Coastal Andhra Pradesh.



 

20 September (Day 5):  Heavy to very heavy rainfall likely at isolated places over Coastal Karnataka ,Kerala and heavy rainfall at isolated places over Odisha, Nagaland, Manipur, Mizoram & Tripura, Gujarat. Thunderstorm accompanied with lightning likely at isolated places over East Uttar Pradesh and Bihar East Rajasthan, West Madhya Pradesh, Jharkhand, Odisha, Coastal Andhra Pradesh.

 

  


  

 

Forecast for any day is valid from 0830 hours IST of day till 0830 hours IST of next day 

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