1

1

REGIONAL CHARACTERISTICS OF THE

2019 SOUTHWEST MONSOON

Sunitha Devi S., Krishna Mishra, S.P.Singh, Naresh Kumar,

A. Kashyapi & K. Sathi Devi

This chapter discusses the observed features of southwest monsoon 2019 depicting

various synoptic situations during the advance, mature and withdrawal phases and the

salient features of the synoptic scale systems.

1.1 Onset and Advance of Southwest Monsoon 2019

1.1.1 Arrival of Southwest Monsoon Current over the Andaman Sea

During mid-May, gradual development of southerly to southwesterly flow occurred

over southern parts of north Indian Ocean. Within a couple of days, the cross-equatorial flow

strengthened and deepened over the Andaman Sea. This feature along with enhanced

cloudiness and rainfall in association with a cyclonic circulation at mid-tropospheric levels

over Andaman Sea, led to the arrival of southwest monsoon (SWM) over south Andaman

Sea, some parts of South Bay of Bengal and Nicobar Islands on 18th May. Sustained rainfall

activity over Andaman & Nicobar Islands and prevalence of southwesterly winds led to

further advance of SWM into some more parts of southeast Bay of Bengal and north

Andaman Sea, remaining parts of Nicobar Islands and southern parts of Andaman Islands

on 25th May. In association with further deepening of south westerlies in the near equatorial

belt and over south & adjoining east central Bay of Bengal, the SWM further advanced into

southernmost parts of Maldives-Comorin area, some more parts of southwest and southeast

2

Bay of Bengal, some parts of east central Bay of Bengal, remaining parts of Andaman Sea

and Andaman Islands on 30th May.

1.1.2 Monsoon Onset over the Main Land

In view of the enhanced cloudiness, strengthening of westerlies and persistent

cyclonic circulation in lower & mid-tropospheric levels over Lakshadweep area and

neighbourhood, the SWM advanced into some more parts of south Arabian Sea, most parts

of Lakshadweep area, some parts of Kerala & south Tamil Nadu, remaining parts of

Maldives-Comorin area, some more parts of south & east central Bay of Bengal and some

parts of northeast Bay of Bengal on 8th June. Thus the southwest monsoon set in over

Kerala on 08th June 2019with a delay of about 7 days as against the normal date of 1st

June.

Fig.1.1: Percentage of rainfall monitoring stations which rained, wind speed and

INSAT derived OLR values

Out of total 14 rainfall monitoring stations considered for declaring the Monsoon

onset over Kerala, 71%, 57% and 50% stations had reported rainfall of 2.5mm or more for

consecutive days on 6th,7th and 8th June respectively. 57% and 93% stations had reported

rainfall of 2.5mm or more for the subsequent days on 9th and 10th June respectively.

Westerly winds strengthened in the lower levels becoming more than 15 knots from 06th

3

June and deepened with Westerly/ West-southwesterly winds up to 600 hPa over the south

Arabian Sea (equator to Lat. 10ºN and Long. 55ºE to 80ºE) from the morning of 7th June.

Persistent convection (indicated by Outgoing Long-wave Radiation (OLR) values <200 Wm-

2) was noticed over the region from 03rd June. The Satellite (INSAT-3D) derived OLR( in the

box confined by Lat. 5-10ºN, Long. 70-80ºE ) was ≤175 W/m2 from 03rd to 07th June and

196.58 W/m2 on 08th June (Fig. 1.1). Though the rainfall criterion was not getting satisfied in

the strict % figure (falling short by about 10%), the meteorological observations conclusively

indicated that widespread and heavy rains are to commence over Kerala, from 08th June.

That is why the onset over Kerala was declared on 08th June.

1.1.3 Further advance of Monsoon

Subsequent to the onset over the mainland, the onset vortex which was in the form of a

cyclonic circulation off the west coast descended down and developed into Very Severe

Cyclonic Storm (VSCS) ‘VAYU’ over east central Arabian Sea during 10th – 17th June. During

this period, the further advance of SWM remained sluggish. It further advanced into:

remaining parts of south Arabian Sea & Lakshadweep area, most parts of Kerala, some

more parts of Tamil Nadu, some more parts of Bay of Bengal, most parts of Mizoram and

some parts of Manipur on 10th June; some parts of central Arabian Sea, remaining parts of

Kerala, some parts of Karnataka, Tamil Nadu, some more parts of Bay of Bengal and some

more parts of northeast India on 14th June and into most parts of Bay of Bengal, remaining

parts of northeast India and some parts of east India on 16th June.

Further advance took place after the dissipation of VSCS ‘VAYU’. SWM further

advanced into: some more parts of central Arabian Sea, peninsular India and of Bay of

Bengal, remaining parts of northeastern states and some more parts of West Bengal on 20th

June; some more parts of peninsular India, some parts of south Chhattisgarh & Odisha,

remaining parts of Bay of Bengal, most parts of West Bengal and some parts of Jharkhand

and Bihar on 21st June; some more parts of Maharashtra, remaining parts of Karnataka,

Telangana, Odisha, Jharkhand, Gangetic West Bengal & Bihar, most parts of Chhattisgarh

and some parts of East Uttar Pradesh on 22nd June; some more parts of Maharashtra and

East Uttar Pradesh on 23rd June; some more parts of central Arabian Sea, Konkan, most

parts of interior Maharashtra, some parts of Madhya Pradesh, some more parts of

Chhattisgarh & Uttar Pradesh and some parts of Uttarakhand on 24th June; remaining parts

of central Arabian Sea, Maharashtra, some parts of north Arabian Sea and south Gujarat

and some more parts of Madhya Pradesh on 25th June and into some more parts of north

Arabian Sea, Gujarat &Madhya Pradesh on 28th June.

4

In association with a well marked low pressure area over southeast Jharkhand &

neighbourhood, SWM further advanced into some parts of East Rajasthan, most parts of

Madhya Pradesh, remaining parts of Chhattisgarh, some more parts of Uttar Pradesh, most

parts of Uttarakhand and some parts of Himachal Pradesh and Jammu & Kashmir on 02nd

July. Subsequently, it advanced into: some more parts of Gujarat, Rajasthan, Madhya

Pradesh and Uttar Pradesh on 03rd July; remaining parts of north Arabian Sea, Gujarat,

Madhya Pradesh and some more parts of Rajasthan on 04th July; some more parts of

Rajasthan, remaining parts of Uttar Pradesh, Himachal Pradesh, Uttarakhand and Jammu &

Kashmir and some parts of Punjab, Haryana, Chandigarh and entire Delhi on 05th July;

remaining parts of East Rajasthan & Haryana and some more parts of West Rajasthan &

Punjab on 09th July; most parts of Haryana and Punjab on 15th July and into remaining parts

of Punjab & Haryana and some more parts of West Rajasthan on 17th July. The SWM further

advanced into remaining parts of West Rajasthan and thus covered the on 19th July, with a

delay of 4 days, against normal date of 15th July.

The isochrones of advance of SWM over the country are given Fig.1.2.

Fig.1.2: Isochrones of advance of southwest monsoon 2019.

5

1.2 Semi-Permanent Systems

1.2.1 Heat Low

The progressive development of a shallow Heat Low over central India during early

May and its migration over to central parts of Pakistan in July is a significant factor of the

establishment of monsoon. The intensity of the Heat Low has been correlated with monsoon

activity quite often (Ramage, 1971). Departure of pressure from normal in this region and

gradient of departures are taken into account. Below normal pressures in the Heat Low

region and above normal pressures in the Peninsula are regarded as favoring monsoon

activity over the country. Pressure gradient would then be strong over the Peninsula which is

conducive to monsoon rains. The Heat Low may also strengthen when the ridge aloft

weakens under the influence of westerly troughs moving further north.

This year, the Heat Low gradually strengthened and got established in its near

normal position in the second week of June. It was mostly seen in its near normal position all

through the season with varying intensity. It started gradually filling up from first week of

September and became less marked in the first week of October.

The lowest and the second lowest values of the Heat Low were:

June: 994hPa (on 30) and 996hPa (on 11)

July: 988hPa (on 7,10) and 992 hPa (8)

Aug: 994 hPa (on 1, 2,6,7, 11) and 996 hPa (on 5, 8, 10, 13)

Sept: 998hPa (on 6,7,12), 1000 hPa (9-11)

1.2.2 Monsoon Trough

During the season, from the Heat Low over Pakistan and neighbourhood, a trough

extends southeastwards to Gangetic West Bengal and thence to Head Bay. The trough line

runs at surface from Ganganagar to Kolkata through Allahabad, with west to southwest

winds to the south and easterlies to the north of the trough line. The position of the trough

line varies from day to day and has a vital bearing on the monsoon rains. Position of trough

line close to the foot-hills has been referred as 'break in monsoon' when there is drastic

decrease in rains over the country, though the Himalayan mountain belt experiences heavy

falls which can cause floods in the rivers originating there. The trough sometimes shifts to

the central parts when monsoon depressions from the North Bay move west / west

northwest-wards across the country.

This year, a shallow Heat trough was seen over the Indo-Gangetic plains from the

first week till the end of June. With the southwest monsoon covering the entire country, it got

established as the monsoon trough to the south of its normal position on 19th July. The

trough remained in its normal position for most of the days till mid August. Subsequently it

6

remained to the south of normal position till 15th September. Thereafter, it got disorganized

and disappeared from the pressure & wind field from 18th Sept.

1.2.3 Tibetan Anticyclone / High

This year, the Tibetan anticyclone was seen either to the south or to the south-

southeast of its normal position up to mid-June. Then it was seen to the east / southeast of

its normal position and got established in its near normal position on 4th July. Almost all

through the month of July it remained either to the northeast or west of its normal position

and in August it remained to the northeast or east. In September, it remained to the east or

southeast on most of the days in first three weeks. It then shifted south-eastwards, thus

becoming un-important in the third week of October.

1.2.4 Tropical Easterly Jet

The TEJ got established over the southern tip of Peninsular India by 1st June with

Minicoy reporting easterlies of 64 kts at 98 hPa level. A wide latitudinal spread of the

easterly jet speed winds was observed during August and September, while during June and

July; the stations over the Peninsular India only reported jet speed winds. The highest wind

speed of 110 kts at 129 hPa was reported at Amini Divi on 11th July.

Apart from Thiruvananthapuram, Chennai, Amini Divi, Minicoy, Karaikal, Mangaluru

and Port Blair, Jet speed winds were reported over Bengaluru, Hyderabad, Machilipatnam,

Karaikal and Visakhapatnam on a few days during the season.

1.2.5 Mascarene High:

The onset of monsoon is associated with a sudden acceleration of winds from the

southern hemisphere towards India, across the equator. The southern hemispheric

circulation regime along the Indian Ocean longitudinal belt is dominated by an anti cyclonic

circulation, around a region of high pressure centered at 30ºS/ 50ºE, known as Mascarene

High, off the coast of Madagascar. Sikka and Gray (1981) suggested that the Mascarene

High undergoes short period intensity fluctuations due to passage of extra tropical waves of

the southern hemisphere. The intensification of Mascarene High strengthens the cross

equatorial flow in the form of Low Level Jet and the corresponding monsoon current over the

Arabian Sea.

The Mascarene HIGH with its mean position at 30.4ºS / 62.3º E was weaker than

normal by 0.5 hPa during the monsoon period (June to September) 2019. It was above

normal by 0.4 and 1.0hPa in June and July respectively and below normal by 2.7 and 0.5

hPa during the months of August and Sept. 2019 respectively.

7

1.2.6 Somali Low Level Jet

The lower tropospheric monsoon flow is essentially concentrated near the coast of

east Africa in the form of a Low Level Jet (LLJ). Fluctuations in the intensity of this LLJ takes

place in association with the passage of extra-tropical westerly waves of the southern

hemisphere, as mentioned above, as well as the location and intensity of the Heat Low.

Strengthening of the LLJ is associated with increased monsoon activity along the west coast

of India.

It may be noted from Fig.1.3 {This is derived as the square root of twice the domain

mean Kinetic Energy of the 850 hPa horizontal wind in the region (50ºE - 70ºE, 5ºS - 20ºN)

[Boos and Emanuel, (2009)]} that there was a spike in the westerly strength during first week

of June, reached its peak in the mid June which can be accounted for the genesis of

Cyclonic Storm ‘VAYU’ and its intensification into a Very Severe Cyclonic Storm having life

period 10th-17th June over the Arabian Sea. It started decreasing becoming weaker than

normal in the third week of June. During the month of July, LLJ remained stronger than

normal during and above normal for rest half. It remained above normal during entire month

of August except for a week’s period when it was below normal and it was above normal for

entire September except for just 2 days when it was below normal. Thus in short, the LLJ

remained stronger than normal for nearly the entire two months of August and September.

This seems to have significant contribution to the prolonged wet spell leading to flood

situation over Maharashtra, Kerala and Karnataka during the period.

Fig.1.3:Somali jet speed index up to 30th September 2019

8

1.3. Other Features:

1.3.1 Off-shore Trough

Off-shore trough along the west coast remained active for only a few days during

June & September (07-08,12-14 & 20-22 June and 02-09 September). It remained active for

more than two weeks during July & August each (03-04 & 09-25 July, 2019 and 03-19

August, 2019).It is not very common that the off-shore trough remains active for such a long

period during August. Its reason may be sought in around three weeks’ above normal

speeds of LLJ during the month of August.

1.3.2 Australian High (normally centered at 30º S/ 140ºE)

The Australian HIGH centered at 32.2ºE / 135.0ºE was stronger than normal by an

average of about 5.0 hPa during the entire monsoon period June to September 2019. It was

above normal by 2.0 & 4.4hPa in the month of June and July and 6.9 hPa in the month of

August and September 2019 respectively.

1.3.3 Sub-Tropical Westerly Jet (STWJ)

The STWJ started shifting northwards from the last week of June. Srinagar reported

84 knots wind (at 190 hPa) at 00 UTC of 28th June. Subsequently, the core of STWJ shifted

to the north of the Himalayas and was not observed over Indian latitudes from 10th July. It

made occasional re-appearances along the latitude of Srinagar during August. In the last

week of September, it shifted southwards as evidenced by the 70 knots westerly wind

reported over Srinagar at 184 hPa at 0000 UTC of 3rd October.

1.4 Synoptic Disturbances over the Indian Monsoon Region

The season witnessed the formation of 14 monsoon Lows including four intense low

pressure systems, comprising 2 Very Severe Cyclonic Storms (VSCS), one Deep

Depression (DD) and one Depression (D) during the season. Of these, 3 formed over the

Arabian Sea and one over the Bay of Bengal. Based on climatological data, about 6

monsoon depressions develop over the Indian region during the SWM season [June to

September] with a standard deviation of about 2.5. Climatologically, two systems form during

July and August and one each during June& September.

The reduced frequency of monsoon depressions as noticed in recent years are

consistent with some of the latest findings that there is a long-term decrease in the intense

monsoon low pressure systems and a corresponding increase in the frequency of weaker

low pressure systems (Ajayamohan et.al., 2010,Krishanamurti et.al, 2013).

9

1.4.1 Storms and Depressions

This year, June & September witnessed the formation of one VSCS each, while 1 DD

formed during August and 1 D during September. Though the frequency of cyclonic storms

is less during the southwest monsoon period, there had been 3 more such years in the

recent 30 years, viz., 1996 ( 2 CS in June, one each over the Bay of Bengal & the Arabian

Sea),2007 (2 in June, both over the Arabian Sea) and 2015 (1 in June over the Arabian Sea

and the other in July, over the Bay of Bengal). The tracks of these systems are given in Fig.

1.4 and their description below.

Fig.1.4: Tracks of VSCSs & Depressions during SWM 2019

1.4.1.1 Very Severe Cyclonic Storm ‘VAYU’ over East central Arabian Sea (10-17 June

2019)

In the leading edge of the monsoon flow, a cyclonic vortex gradually concentrated

into a D over Southeast Arabian Sea (AS) and adjoining Lakshadweep & Eastcentral ASin

the early morning of 10th June. It gradually intensified into Cyclonic Storm 'VAYU' by late

night of 10th June over eastcentral & adjoining southeast Arabian Sea. It further intensified

into a VSCS by late night of 11th June over Eastcentral Arabian Sea. Skirting Saurashtra

coast during 13-14 June, it started moving away from the coast, weakened into a Severe

Cyclonic Storm on 16th early morning and then into a Cyclonic Storm in the night of 16th

June, over north AS. Then it started recurving eastwards and gradually weakened into a D

by the afternoon of 17th. It weakened further and lay as a Well Marked Low Pressure Area

over Northeast Arabian Sea and adjoining Saurashtra& Kutch in the night of 17th. It further

weakened into a Low Pressure Area and lay over Kutch and adjoing areas in the morning of

18th June.

10

1.4.1.2 Deep Depression over northwest Bay of Bengal off north Odisha-West Bengal

coasts (6-9 August, 2019)

A low pressure area concentrated into a D over northwest Bay of Bengal (BoB) off

north Odisha - West Bengal coasts in the morning of 6th August. It intensified into a Deep

Depression over the same region in the early morning of 7th and crossed north Odisha-West

Bengal coasts close to north of Balasore in the afternoon of 7th. It weakened into a D over

northeast Chhattisgarh & neighbourhoodin the early morning of 8th August, further into a

well marked low pressure area over southeast Rajasthan & neighbourhood in the evening of

9th August and into a low pressure area over northwest Arabian Sea and neighbourhood in

the evening of 12th.

1.4.1.3 Very Severe Cyclonic Storm ‘HIKAA’ over the Arabian Sea (22-25September

2019)

A Depression formed over Eastcentral and adjoining Northeast Arabian Sea off

Gujarat coast on 22nd September. Moving nearly westwards, it gradually intensified into

Cyclonic Storm 'HIKAA' over Northeast and adjoining Eastcentral Arabian Sea on 23rd early

morning and into a Severe Cyclonic Storm over Northeast and adjoining Northwest and

Central Arabian Sea by the afternoon of the same day. Moving nearly westwards further, it

rapidly intensified into a VSCS in the early morning hours of 24th over Northwest and

adjoining Westcentral Arabian Sea. Moving west-southwestwards, it crossed Oman coast

close to north of Duqm between 1930 and 2030 hours IST of 24th September as a VSCS.

After crossing the coast it moved westwards further and weakened rapidly.

1.4.1.4 Depression over Gulf of Kutch and adjoining areas (29 September-01 October,

2019)

A low pressure area formed over northeast Arabian Sea & adjoining coastal areas of

Saurashtra & Kutch on 28th September. It concentrated into a Depression over Gulf of Kutch

and neighbourhood in the evening of 29th, close to Kandla (Gujarat). It moved east-

northeastwards and weakened into a well marked low pressure area over southeast

Rajasthan & neighbourhood in the morning of 01st October.

1.4.2 Low Pressure Areas/Well Marked Low Pressure Areas

Apart from the above depicted intense monsoon Lows, 10 more low pressure areas

(LPA) formed during the season. Their monthly distribution had been 1 each in June &

September and 4 each in July & August. Out of these 10 LPAs two became well marked.

Approximate track followed by these systems are given in Fig.1.5.

11

Fig.1.5: Tracks of low / well marked low pressure areas 2019

Apart from VSCS VAYU, one more low pressure area formed in the month of June

over northeast BoB during 20th -22nd June. Moving inland, it became less marked over

interior Odisha and adjoining areas of Jharkhand & Chhattisgarh. The next one formed on

30thJune over northwest Bay of Bengal & adjoining areas of north Odisha, West Bengal and

Bangladesh. It became well marked on 1 July over the northwest Bay of Bengal and

adjoining areas of West Bengal and Odisha coast. It lay as a low pressure area over central

parts of Uttar Pradesh and adjoining Madhya Pradesh on 5 July and became less marked on

6th July.

The third low pressure area formed in the evening of 6th July, over western parts of

Bihar and adjoining Jharkhand. It became well marked on 9 and became less marked on

11th July. The fourth low pressure area formed over northwest Bay of Bengal and adjoining

coastal areas of west Bengal on 26th July. It became less marked on 27th July. Fifth pressure

area also formed over land, ie, over east Madhya Pradesh and adjoining Chhattisgarh on

30th July. This low pressure area became less marked on 31st July.

Besides the DD in August, four more low pressure areas formed during the month.

Three low pressure areas formed over Bay of Bengal during the period (12-18 Aug), (24-25

Aug) and (29-30Aug). Out of these three low pressure areas, one became well marked low

pressure area. Fourth low pressure area formed over land (central parts of Gangetic West

Bengal and Jharkhand) during (18 - 22Aug).

.

12

Apart from VSCS HIKAA and another short lived D, one more low pressure area

formed during September. It formed over northwest Bay of Bengal & neighbourhood on 2nd

September, moved west-northwestwards upto north Madhya Pradesh before becoming in-

significant on 16th September.

The number of Low Pressure System (LPS) days [low pressure areas and

Depressions combined] had been 4 in June, 15 in July, 21 in August and 17 in September

against a normal of 11, 14, 17 & 16 during the respective months. The total number of LPS

days had been 57 as against the normal of 57 (Mohapatra, 2008). The VSCS days are not

counted as their direct contribution to the rainfall had been nominal.

1.4.3 Upper Air Cyclonic Circulations

There were 137 upper air cyclonic circulations (in lower, mid and uppertropospheric

levels) which formed during the season. The month wise distribution of these is: 36, 32,

34&35during June, July, August and September respectively.

1.4.4 Eastward Moving Cyclonic Circulations/Western Disturbances

During the month of June, about 6 (six) western disturbances (WDs) affected

northwest India during 1st & 2nd June, 3rd – 8th June, 11th – 14th June, 13th – 17th June,

23rd – 27th June and the 6th one from 29th June – 2nd July 2019. Out of these, three WDs

caused fairly widespread to widespread rainfall/thunderstorms over Western Himalayan

Region and isolated to scattered rainfall/thunderstorm activity over adjoining plains.

During the month of July,4WDs affected northwest India during 4th – 5th July, June,

7th – 9th July, 12th – 18th July, 25th – 30th July. Out of these, three of them caused fairly

widespread to widespread rainfall/thunderstorms over Western Himalayan Region upon their

interaction with the monsoon flow.

In total, there were 21 eastward moving systems as upper air cyclonic circulations

and troughs. The month wise distribution is 6 in June, 5 in July, 7 in August and 4 in

September.

1.5 Significant weather events during the season

Fig. 1.6 depicts the met. Sub-divisions or parts thereof, which experienced high

impact weather events like, floods, landslides, Thunderstorms & Lightning, Dust storms and

Heat waves during the southwest monsoon season (June- September) along with the dates.

Fig.1.6 also indicates areas that experienced isolated extremely heavy rainfall (Rainfall

amount ≥20 cm reported during the 24 hours ending at 0300 UTC) events during the

season.

13

Fig.1.6: High Impact Weather Events pertaining to events & dates as per legends

The season witnessed a very large number of ‘High Impact weather events, of which

‘floods’ remained to be the most frequent and widespread phenomenon. It may be noted

that, almost all meteorological sub-divisions experienced one or other category of severe

weather event during the season. Incessant rainfall associated with the formation and

14

movement of the monsoon low pressure systems in the presence of strong cross equatorial

flow often caused flood situations over various areas during different parts of the season

Maharashtra experienced one of the worst flood situations during past 50 years, due to

frequent heavy rain spells and several extremely heavy rain events, especially during August

& September.

Several record-breaking extreme rainfall and resultant Flood events caused human

casualty and property damage in states including Maharashtra, Karnataka, Kerala, West

Bengal, Odisha, Uttar Pradesh and Madhya Pradesh during later part of July to September.

Localised and brief flood events occurred due to record breaking rain events in Jammu &

Kashmir on 30th& 31st July and in Gujarat on 1st August.

1.6. Low Pressure Systems over West Pacific Ocean/ South China Sea/South Indian

Ocean

1.6.1 West Pacific Ocean/South China Sea

There were, in all, 19 low pressure systems (reaching the intensity of Tropical

depression and above) in the northwest Pacific Ocean / South China Sea during June –

September 2019. On an average, about 2 systems form during June, 4 in July and 5 each in

August & September. The month wise break-up of this year is given below:

Low Pressure Systems June July August September TOTAL

Tropical Depression (T.D.) 01 01 00 01 03

Tropical Storm (T.S.) 01 03 03 02 09

Typhoon/Super Typhoon 00 00 03 04 07

TOTAL 02 04 06 07 19

1.6.2 South Indian Ocean

No low pressure system (having intensity more than D) was reported in south Indian

Ocean during June- September 2019.

1.7 Withdrawal of Southwest Monsoon

The isochrones of withdrawal of monsoon are given in Fig.1.7. Due to the prevalence

of an active Inter Tropical Convergence Zone, across central India, north Indian Ocean,

extending upto western north Pacific Ocean, the withdrawal of southwest monsoon was

delayed upto the 1st week of October. Anti cyclonic circulation in lower levels over Rajasthan

could only be established after 05th October. This led to the most delayed commencement of

withdrawal since 1961. Against normal date of withdrawal of SWM 01st September, the

15

Monsoon Withdrawal commenced only on 09th October.In 1961 it was 01st October followed

by 30th September in 2007.

Fig.1.7: Isochrones of withdrawal of South West Monsoon 2019.

It withdrew from some parts of Haryana, Punjab and north Rajasthan on 09th

October. With the increase in dominance of mid-latitude circulation regime over the northern

half of India and consequent reduction in moisture led to further withdrawal of southwest

monsoon from entire Northwest India, some parts of West Bengal, Bihar, Jharkhand,

Chhattisgarh, Madhya Pradesh, Gujarat and north Arabian Sea during 10th -12th October;

from entire north Bay of Bengal, some parts of central Bay of Bengal, entire Odisha,

Chhattisgarh, some parts of Coastal Andhra Pradesh, some parts of Telangana, most parts

of Maharashtra, some parts of North Interior Karnataka, entire north Arabian Sea and some

parts of central Arabian Sea during 13th-15th October. Thus in a rapid phase, the Southwest

Monsoon withdrew from the entire country), giving way to simultaneous commencement of

northeast monsoon rains on 16th October, 2019.

16

1.8 Concluding remarks.

The cumulative seasonal rainfall over the country as a whole was 110% of its Long

Period Average (LPA).

Southwest monsoon set in over Kerala on 8th June, with a delay of 7 days. Further

progress over south peninsular & central India was also on a sluggish phase mainly

due to the formation of very severe cyclonic storm ‘Vayu’ over the Arabian Sea

during 10th -17th June. It covered the entire country on 19th July, with a delay of 4

days from normal.

Delay in the advance of monsoon over major parts of central and adjoining south

Peninsular India resulted in large rainfall deficiency in the month of June, which was

33 % less than its LPA.

This year, June & September witnessed the formation of one VSCS each, while 1 DD

formed during August and 1 D during September. Though the frequency of cyclonic

storms is less during the southwest monsoon period, there had been 3 more such

years in the recent 30 years, viz., 1996 (2 in June, one each over the Bay of Bengal

& the Arabian Sea), 2007 (2 in June over the Arabian Sea) and 2015 (1 in June over

the Arabian Sea and the other in July, over the Bay of Bengal).

The reduced frequency of monsoon depressions as noticed in recent years (with

exception of years like 2007) are consistent with some of the latest findings that there

is a long term decrease in the intense monsoon low pressure systems and a

corresponding increase in the frequency of weaker low pressure systems.

Due to the prevalence of an active Inter Tropical Convergence Zone, across central

India, north Indian Ocean, extending upto western north Pacific Ocean, the

withdrawal of southwest monsoon was delayed upto the 1st week of October. Though

the withdrawal commenced from northwest India on 9th October as against the

normal date of 1st September, it withdrew on a rapid phase from the entire country by

16th October (against the normal date of 15th October), giving way to simultaneous

commencement of northeast monsoon rains.

Several record breaking extreme rainfall and resultant Flood events caused human

casualty and property damage in states including Maharashtra, Karnataka, Kerala,

West Bengal, Odisha, Uttar Pradesh and Madhya Pradesh during later part of July to

September.

References :

17

Ajayamohan R.S., Merryfield W.J., &Kharin V.V., 2010, ‘Increasing trend of synoptic activity & its relationship with extreme rain events over central India’, Jl. of Climate, 23, 1004 – 1013.

Boos, W.R and Emanuel, K.A., 2009: ‘Annual intensification of the Somali Jet in a

quasi-equilibrium framework: Observational composites’, Quart. J.R. Met. Soc, 135, 319-335.

Krishnamurti, T.N., Martin, A.,Krishnamurti, R., Simon, A, Thomas,A., Kumar,V., 2013 ‘Impacts of enhanced CCN on the organization of convection and recent reduced count of monsoon depressions’, Clim. Dyn. 41, 117-134.

Mohapatra, M., 2008: ‘Sub-divisional summer monsoon rainfall over India, in relation

to low pressure systems over the Bay of Bengal and adjoining land regions during 1982-1999’, Mausam, 59,3, pp. 327-338.

Ramage,C.S., 1971: ‘Monsoon Meteorology’ Academic Press, New York and

London, 296 pp. Ramaswamy, C., 1965: ‘On synoptic methods of forecasting the vageries of

southwest monsoon over India and neighbouring countries’, Proc. Symp. Meteor. Results IIOE, Bombay, pp. 317-349.

Sikka, D.R., and W.M.Gray, 1981: ‘Cross-hemispheric actions and the onset of summer monsoon over India’, International conference on Sci. Results of monsoon experiments, Bali, Indonesia, 26-30 Oct., 1981, pp. 3-74 to 3-78.