More rain for South India; storms return to central region

FROM THE NEWS EDITION: http://www.downtoearth.org.in/news/storms-to-return-to-central-india-rain-to-the-south-51919

(FIRST UPLOAD NOVEMBER 28TH 2015, UPDATED 30TH NOVEMBER 2015)

A new upper air trough has hit India, changing the weather conditions across the central and southern regions of the country

Thunderstorms are set to return in parts of Central India after they brought severe weather a month ago. A new upper air trough (see image below) is set to reach India, November 30 onwards, which will create conditions favourable for outbreak of storms. As the week progresses, this trough and associated thunderstorms will move eastwards, covering states like Rajasthan, Madhya Pradesh, Uttar Pradesh, Chhattisgarh, Jharkhand and possibly Bihar. 

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Map showing winds in upper parts of troposphere on 1st December 2015. The axis of trough is shown as dashed red lines over Western India. (Courtesy- weatheronline.co.uk )

Troughs are elongated low pressure regions in Earth’s troposphere (lowermost part of atmosphere where weather systems exist) that are powerful enough to change a bright sunny morning into a stormy afternoon. 

The round of thunderstorms in Central India will begin from November 30, Monday. These will be experienced in the northern and western parts of Madhya Pradesh and South-eastern Rajasthan (Kota-Sawaimadhopur) for two days.

On December 2, a large region comprising of North-eastern Madhya Pradesh, Southern Uttar Pradesh and parts of Jharkhand and Bihar can get some rain. December 3 onwards, the weather will start normalising in Central India. These thunderstorms would be capable of bringing localised heavy downpours, lightning and some winds.

Possibility of hailstorms

The thunderstorms may turn severe, given the availability of required conditions. The freezing level (pressure level in troposphere with temperature of 0°C) has dropped below normal in Madhya Pradesh which will be ideal for occurrence of hailstorms. Hailstorms are anticipated in south-east Rajasthan (around Kota), Northern Madhya Pradesh (Guna-Gwalior belt) and neighbouring districts of Uttar Pradesh. They are expected to progress towards North-western Madhya Pradesh and adjoining parts of Uttar Pradesh on Wednesday.

As per agricultural experts, this round of rain will be beneficial to Rabi as it stands to improve the soil moisture. However, localised heavy downpours (or hailstorms, if they occur) will have a potential to damage the horticulture and harvested crops in these areas, especially Madhya Pradesh. After December 3, northerly winds will dominate in many parts of India including Central India and enable drop in temperature in these areas, which have been above normal in November.  

Wet week for Southern states

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District rainfall map of Tamil Nadu (1st October to 25th November period) showing districts with normal and excess rainfall. Courtesy- Indian Meteorological Department (Courtesy- Indian Meteorological Department)

Coastal and interior parts of Tamil Nadu recently witnessed heavy north-east monsoon rain which caused massive flooding. North-east monsoon period (October to December) is a major period of rain activity in Southern India and accounts for 48 per cent of Tamil Nadu’s annual rainfall as per a India Meteorological Department report.

Under the influence of a new low pressure system in southern Bay of Bengal, parts of Andhra Pradesh, Pondicherry and Tamil Nadu will witness rain in this week. Places in Tamil Nadu will get occasional moderate to heavy rain in this week that can create fresh water logging in cities like Chennai and add to existing problems due to flooding. There will be flooding potential in coastal areas of Andhra Pradesh as well.

Hailstorm lashes parts of Rajasthan, Madhya Pradesh and Uttar Pradesh

FROM THE NEWS EDITION: http://www.downtoearth.org.in/news/hailstorm-lashes-parts-of-rajasthan-madhya-pradesh-and-uttar-pradesh-51643 (DATED 29TH OCTOBER 2015)

Temperatures dip in a number of places, experts say occurrence good for Rabi crops

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Hailstorm in Jhansi area of Uttar Pradesh. According to weather experts, hailstorm at this time of the year is not a normal phenomenon Credit: Ritesh Garg

An upper air circulation brought on by western disturbance caused hailstorm in parts of eastern Rajasthan, Madhya Pradesh and Uttar Pradesh on Wednesday.

Lightning due to severe weather claimed six lives in Mathura, Aligarh, Allahabad and left over a dozen injured.

As per initial reports, hailstorm was reported from Bharatpur, Alwar, Jaipur and Sikar in Rajasthan. Available Doppler radar images taken on Wednesday afternoon indicated more incidents of hailstorm in isolated areas of east and north-east Jaipur.

Following hailstorm, temperatures dipped in Jaipur. The pink city recorded 21.7 mm rainfall on Wednesday and the minimum temperature touched 12.6°Celsius, 4°Celsius below normal, on Thursday morning.

The Bundelkhand region of Madhya Pradesh was severely affected. Areas like Ashoknagar, Shivpuri, Khurai, Malthon, Damoh, Chattarpur, Dabra, Gwalior, Anchal Kheda, Sevda and Datia witnessed severe hailstorm on Wednesday. Coin-sized hails fell for a long time in many areas of the state. Here also, temperatures registered a dip.

Jhansi, Mathura, Aligarh and Baghpat districts in Uttar Pradesh witnessed hailstorm mostly on Wednesday afternoon. Heavy rainfall was reported from Jhansi, Lucknow, Kanpur, Farrukhabad and Banda. Strong winds uprooted several trees and electric poles as a result of which telecommunication and power supply were disrupted.

Jhansi's maximum temperature on Wednesday touched 22.1°Ceslius, registering a departure of -10°Celsius from normal.

Was the hailstorm normal?

According to weather experts, hailstorm at this time of the year is not a normal phenomenon. If one looks at the climatological table (1971-2000) of these places, the mean number of days with hailstorm in October is zero.

What is even more striking is that as per climatology, Jhansi never gets hailstorm (the mean number of days with hailstorm is zero for all months).

However, observations clearly suggest that hailstorms are becoming more and more frequent. Since 2011, parts of Rajasthan such as Sikar and nearby areas have been experiencing hailstorm practically every year in the January-April period, but perhaps it is for the first time that it occurred in October.

Some amount of rainfall will be beneficial for Rabi crops at this time. According to Bharatiya Kisan Union general secretary Anil Malik, hailstorm at this time of the year will prove to be beneficial for Rabi crops. "It would have proved disastrous if the hailstorm had occurred during February and March," he said.

N Chattopadhyay, deputy director general of meteorology (agricultural meteorology), India Meteorological Department, said as the Rabi sowing period is going on, Wednesday's rains in parts of Uttar Pradesh and Madhya Pradesh will be beneficial for agriculture. Such rain helps in increasing soil moisture which is very important for proper growth of crops.

However, strong winds and hailstorm have reportedly damaged standing crops and vegetables in Madhya Pradesh and Uttar Pradesh. Some areas in these two states have witnessed back to back hailstorms since the past few years. Several areas of Madhya Pradesh were badly beaten by hailstorm during March-April this year.

Crop damage is a bad news for drought-hit farmers. This year, the south-west monsoon brought scanty rainfall in eastern Madhya Pradesh and Uttar Pradesh. The eastern part of Madhya Pradesh received 29 per cent below normal rainfall this time, eastern Uttar Pradesh received 47 per cent below normal whereas western Uttar Pradesh received 43 per cent below normal rainfall.

Fewer Doppler radars

Doppler radars play a vital role in detecting lightning and hailstorm. Based on these detections, people can be warned well in advance about such occurrences. Hence, for an efficient forecasting, there must be a high coverage of these radars. United States has an extensive grid of about 155 Doppler radars as against just 16 in India.

Out of these 16, three (in Hyderabad, Lucknow and Nagpur) are non-functional at present. Big states such as Madhya Pradesh and Uttar Pradesh have just two radars in Bhopal and Lucknow respectively. These installed (S band) Doppler radars work best only within a radius of 250 km.

As Lucknow's radar was non functioning on Wednesday, most areas in Uttar Pradesh (where both hailstorm and lightning were reported) were out of coverage area. Even Bhopal's radar could not properly track hailstorm beyond its 250-km range. In north-central Madhya Pradesh, large areas were out of coverage because of their distance from Bhopal's radar.

Last year during February-March when severe hailstorms hit many parts of India, more than half of the Doppler radars in India were not working. Some of them were broken like Nagpur's radar and others were undergoing maintenance. Thus, India has a long and unfortunate history of "out of order" radars.

India is not a weather-ready nation. As per records, lightning strikes killed over 2,500 people in India in 2014 as compared to 26 in the US during the same period.

Possibility of severe thunderstorms in parts of India

FROM THE BLOG EDITION : http://www.downtoearth.org.in/blog/possibility-of-severe-thunderstorms-in-parts-of-india-51602 (27TH OCTOBER 2015)

Existing weather system can even cause hailstorms in eastern Rajasthan, northern Madhya Pradesh and parts of Uttar Pradesh

This past weekend, an upper air trough (western disturbance) significantly impacted North India, especially Jammu and Kashmir. As anticipated, maximum temperatures dipped by 12-15°C in most places in the state on Sunday, October 25, due to rain and snow. Jammu-Srinagar highway was closed to traffic due to frequent landslides. Rain caused water logging in Srinagar on Sunday. Thundershowers were also reported in Punjab and Haryana. 

This upper air trough is set to move southwards till central India during this week and set the stage for thunderstorms and rain in parts of eastern Rajasthan, Madhya Pradesh, north-western Chhattisgarh, Uttar Pradesh, Vidarbha, Bihar and Jharkhand till Friday, October 30. 

What does this atmospheric pattern mean? 

 

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GIF showing the approach of 'western disturbance' (represented by the reddish patch) from Pakistan into north-central India between October 27 and 30, 2015 (Courtesy: COLA/IGES)

 

A section in my previous blog explains what upper air troughs are. Usually, such troughs don't dip as low as central India in October. The "unseasonal" rain India saw in February and March this year was also because these troughs were very intense and had dipped more than usual. Such troughs move from west to east and ahead of their arrival, they destabilise the troposphere (part of atmosphere where weather systems exist), creating conditions for thunderstorms. Under ideal conditions, these thunderstorms intensify into severe thunderstorms and are capable of producing heavy rain in a short time, strong lightning, hail and strong winds. 

Associated with such upper air troughs, which are typically observed at around 30,000 feet, are cyclonic circulations or low pressure regions with anticlockwise spin of air in the northern hemisphere, in the lower levels of troposphere (around 20,000 feet). These circulations typically develop because of upper air troughs and they move along with the troughs. The image above shows one such circulation coming from Pakistan to north-central India by October 30. This circulation will reach northern Madhya Pradesh by Wednesday, October 28, and travel south-east near Uttar Pradesh by Thursday, October 29.

What is expected from this setup? 

 

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Area circled in grey has the highest chance of witnessing severe thunderstorms on October 28 and 29

 

Such troughs are known to bring a lot of cold air to the region where they are present from regions which are to their north. Cold air is dense and reduces the height of the freezing level in that region. In the troposphere, the temperature of air decreases with an increase in height. Freezing level is that level in the troposphere which has a temperature of 0°C. Above that level, the temperature of air is negative and towards the Earth's surface, the temperature of air is positive.

If this level is further away from the Earth's surface, hailstones get enough time to melt after they have precipitated from thunder clouds. The positive temperatures between this freezing level and surface of the Earth are responsible for this melting. If this level is nearer the ground, hailstones reach the ground without evaporating much and what we get is hail. 

On Wednesday, October 28, severe thunderstorms capable of producing rain and lightning can be expected in eastern Rajasthan (areas east of Jaipur, Sawaimadhopur), parts of Madhya Pradesh (particularly around Jhansi-Gwalior) and parts of Uttar Pradesh (areas west of Kanpur-Allahabad) adjoining northern Madhya Pradesh and Rajasthan. The freezing level in these areas has reduced below normal and owing to high instability, some  thunderstorms in these regions can even produce hail. 

On Thursday, October 29, the region of thunderstorms and rain will shift slightly eastwards. Eastern Madhya Pradesh, north-western Chhattisgarh, eastern Uttar Pradesh (around Allahabad), and parts of Bihar and Jharkhand will get rain. Some areas may also get hail. People living in these areas must remain alert. 

Climatologically speaking (based on 1971-2000 data), these areas had not seen a single day of hail. Hence, if the anticipated hail arrives, it will be considered a bit unusual. 

Update on low pressure systems

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Approximate positions of low pressure systems (denoted by 'L') in the Arabian Sea and the Bay of Bengal according to a satellite image as of the afternoon on October 27 (Courtesy: India Meteorological Department)

According to IMD's update on Tuesday afternoon, the Arabian Sea low pressure has become a "well-marked low pressure" system. Data from the Thai Meteorological Department suggests that this system has a mean sea level pressure of 1006mb while the system in the Bay of Bengal has mean sea level pressure of 1008mb. But, as per present weather models, the low pressure in the Bay of Bengal isn't expected to intensify much due to unfavourable conditions. It will lead to the onset of northeast monsoon in parts of South India on October 28 and won't cause any threat to India. 

However, due to marginally favourable conditions, the Arabian Sea low pressure can intensify slightly as it moves towards Gulf of Aden. Present weather models don't expect this low pressure to track towards India and hence, it isn't expected to threaten India.

Rainfall, snow expected in northern India over weekend

From the blog edition: http://www.downtoearth.org.in/blog/rainfall-snow-expected-in-northern-india-over-weekend-51565

A variety of weather events will be witnessed in India in the coming week 

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The satellite image taken on October 23 shows the position of the western disturbance (circled in red) and the low pressure system (denoted by L) in the Bay of Bengal Credit: IMD

A powerful upper air trough (popularly called western disturbance by the India Meteorological Department) is all set to hit northern India by this weekend.

As a result of it, the hilly areas of Jammu and Kashmir, Himachal Pradesh and Uttarakhand will receive snowfall from Saturday (October 24) till Wednesday (October 28). 

The maximum amount of rainfall (to be witnessed in the low-altitude areas of these three states) and snowfall will be witnessed from Saturday to Monday. During this period, landslides will be witnessed on the Jammu-Srinagar highway, which will likely to remain shut for a few days.

Temperatures in much of the Kashmir Valley (including Srinagar) are already above the freezing point. Hence, the expected rainfall may create water logging and flooding. Travellers should remain cautious.

Along with rainfall and snowfall, thundershowers are also expected in Punjab, Chandigarh, parts of Haryana, Delhi and the National Capital Region from Sunday to Tuesday.

Arrival of winter

Winter has gradually started arriving in the hilly areas of north India. From Saturday onwards, maximum temperatures will decrease by an average 2-3° Celsius in Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana and Chandigarh due to rainfall.

Rainfall will bring about a temporary rise in the minimum temperatures till October 26, but after that, minimum temperatures will significantly fall in these areas bringing colder nights.

Already several places in northern India are experiencing chilly conditions. Leh in Jammu and Kashmir recorded a minimum temperature of -1.9°Celsius on Friday morning.

Other places such as Gulmarg (J&K) recorded a minimum temperature of -1.4°Celsius (3° Celsius below normal), Srinagar recorded 5.5° Celsius, Pahalgam and Keylong (Himachal Pradesh) recorded 0.6° Celsius and Manali stood at 4.6° Celsius.

Not to be outdone, the plains in north India have also started witnessing mild winter conditions. Places in Punjab and Haryana are witnessing minimum temperatures in the range of 14-17°Celsius. Even Safdarjung in Delhi recorded a minimum temperature of 17.3°C on Friday morning.

Southern story

However, south tells a different story. If one travels a bit southwards, a contrast in the weather will be observed.

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The image shows maximum temperatures in several places across India on October 19, 2015. Red patches indicate maximum temperatures above 35°Celsius. Credit: RMC Delhi/IMD

The maximum temperatures in the past 15 days have been consistently in the range of 35-40°Celsius in states such as Maharashtra, parts of Karnataka, Telangana and Andhra Pradesh.

In western India, a few places in the Kutch area of Gujarat recorded maximum temperatures above 40°Celsius.

Mumbai is also "boiling" as was expected (read http://www.downtoearth.org.in/blog/tropical-depression-forms-in-the-arabian-sea-51447).

On October 16, a 43-year-old record was broken in Mumbai. The day was the hottest in October in Santa Cruz area. On this day, the maximum temperature stood at 38.6°Celsius, which was 5.2°C above normal. Earlier, 37.9°Celsius was recorded on October 23, 1972.

Generally, Mumbai is not known for so much heat, but the maximum temperatures have remained above 35°Celsius for several days. Places in Vidarbha are witnessing maximum temperatures in the range of 35-40°Celsius.

Such high temperatures are affecting Maharashtra's agriculture. The state's water stock is at its lowest in the past five years due to poor monsoon this year. 

Weather conditions will continue to stay hot in western and central India, as no significant change in weather conditions is anticipated in the remaining days of October.

The temperature contrast between north and south India is a typical feature the country witnesses every year in October after the south-west monsoon withdraws.

This year, the south-west monsoon withdrew from entire India on October 19, as per the IMD. Dry, northerly winds in north India are keeping the skies clear. This, in turn, is causing radiative cooling (a process in which heat from the Earth's surface is radiated back to the space). Central and western India witness high temperatures in October due to the prevalence of dry winds. The lack of any rain-bearing system during this period is also responsible for this situation. But, this time the duration of such high temperatures is more than normal.

Strong low-pressure system possible in the Bay of Bengal

At present, there are two low-pressure systems in the north Indian Ocean. One is in the Arabian Sea, off the shore of Lakshadweep and another is in the Bay of Bengal, off the shore of Sri Lanka.

Weather models suggest intensification of this system in the Bay of Bengal early next week. If we believe in the present forecast, the system will reach near the Tamil Nadu coast by Wednesday. It may bring heavy rainfall in the coastal areas of Tamil Nadu and Andhra Pradesh. With this, the much awaited north-east monsoon is anticipated to commence in southern India.

The southern peninsula (particularly the eastern coastal areas of South India) gets a large percentage of its annual rains because of the North-East Monsoon. Tamil Nadu is known to receive about 48 per cent of its annual rainfall between October and December, which is known as the North-East Monsoon period. There are several criteria for declaring the onset of the North-East Monsoon. IMD usually declares this around October 20, mainly after an increase in rainfall activity in the coastal areas of Tamil Nadu and Andhra Pradesh.

Also, we cannot rule out the possibility of the low pressure intensifying into a tropical depression or even a tropical storm. Hence, it will be monitored closely and an update will be given, if at all, it poses any significant risk for the south-east coastal areas of India.

El Niño not solely responsible for poor monsoon

FROM BLOG EDITION: http://www.downtoearth.org.in/blog/el-ni-o-not-solely-responsible-for-poor-monsoon-51201

This season, parts of India witnessed one of the driest monsoon spells

India's crucial south-west monsoon season is coming to an end. With less than ten days to go in the official wind up of the season, India is all set to witness another year of below normal rain. All India seasonal rainfall departure will set close to -15 per cent (with slight variance possible). A departure of -15 per cent means rain has been 15 per cent below normal. As per India Meteorological Department (IMD), a departure of -15 per cent comes under a broad "normal" rain category which runs from +19 per cent to -19 per cent. However, things aren't that normal in most of the 16 (out of 36) meteorological subdivisions which till date have recorded "deficient" rain. With a departure of -46 per cent between June 1 and September 20, Eastern Uttar Pradesh tops the list. It is followed by Western Uttar Pradesh at -44 per cent, Punjab at -41 per cent and Haryana at -39 per cent.

This year's monsoon has been dicey and full of ups and downs. Speculations about El Niño affecting India's monsoon were there since early 2015. But the first blow to the chances of a good monsoon came on April 22, when the IMD issued the first part of Long Range Forecast (LRF) of monsoon. This suggested that India would get 93 per cent of normal rain of 89cm (with a variance of plus minus 5 per cent). On June 2, in the second part of LRF, IMD downgraded their previous forecast. The updated forecast suggested that India would get 88 per cent of normal rain in the monsoon period (variance of plus minus 4 per cent). But, to everyone's surprise, the monsoon's mood remained very good during the onset phase (i.e in June). In this month, India received 16 per cent above normal rain. Thirteen subdivisions recorded excess rain, 20 recorded normal rain and only 3 recorded deficient rain. Performance of rain was impressive in Jammu and Kashmir, Rajasthan, Western Madhya Pradesh and other parts of Central India. This was welcoming news for the citizens and it even brought back their hopes of a normal monsoon. Already debt-ridden but encouraged by good rain, farmers in drought-prone areas of Maharashtra like Marathwada took fresh loans and invested heavily in their fields in June hoping for a good harvest. The situation was similar in other parts of India too. No one even imagined what was in the offing.

 

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IMAGE 1- All India rainfall in the month of June '15. Courtesy IMD

Come the fourth week of June, things started changing. Central India witnessed a big dry spell of the monsoon which lasted for around one month. Such dry and wet spells are regular features during the season. Their intensity, frequency and time of occurrence play a very vital role in monsoon's performance, which in turn, influences the agricultural productivity. But, the one month long dry spell which Maharashtra, Gujarat and Madhya Pradesh witnessed was very severe. It severely damaged the kharif crops and even led to their complete destruction at many places in Marathwada and western Maharashtra (Madhya Maharashtra) where irrigated area is too low. It also kicked off drought conditions and agrarian crisis in these areas, leading to acute shortage of drinking water and fodder for thousands of cattle. For the first time in the history of Maharashtra, cattle shelters were set up in the month of August in Marathwada. At the end of July, India's seasonal rain which was 16 per cent above normal in June came down to 5 per cent below normal. The trend continued in August, due to which the amount of seasonal rain further came down to 11 per cent below normal. And on September 20, we are at 14 per cent below normal. This is how June's rain fooled the farmers in suicide-prone areas of Maharashtra. The farmers wouldn't have gone for early sowing had June's rain been scanty and in such a case, the loss certainly would have been lesser than what it is right now.

The overall poor performance of the monsoon confirms the influence of suppressing factors like El Niño. But why was June an exception? Where was El Niño in June? Was it absent?

 

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IMAGE 2- Schematic representation of wet phase of MJO over India. This is reflected by stormy and wet weather over India. Courtesy: Climate.gov/Fiona Martin

El Niño was very much present in the month of June! It was trying its best to suppress India's monsoon but it was the Madden-Julian Oscillation (MJO) which gave it a "fight". MJO was discovered by two atmospheric researchers—Roland Madden and Paul Julian in the early 1970s. Simply put, MJO is an atmospheric disturbance which travels around the world in the tropical regions over an average period of 30-60 days. This disturbance propagates eastwards with time and with a varying intensity. The most important property of MJO is that it influences the clouds/rain i.e the process of convection in the areas it travels through. It has two "faces". One face or phase boosts the process of clouds/rain (called the wet phase) while the other one suppresses it (called the dry phase). India's monsoon gets benefitted whenever there are wet phases over the nation. This is because such a phase helps in the rising motion of moist air, which is necessary for cloud formation. The more intense it is, the more rain that particular region gets. In a sense, it counters the negative effects of El Niño for a certain period of time. But when a dry phase enters, it suppresses the rainfall and under the prevailing El Niño conditions, the suppression factor is pretty strong. MJO has dipole nature as can be seen from the above image. Over India, there is a wet phase, but over the Pacific there is dry phase at the same time. This is because the warm moist air that rises over India diverges and cools at upper levels of the atmosphere. This cool and dry air then sinks over the Pacific (see the arrow) causing lack of clouds/rain there.

MJO became active in early June of this year and the Indian subcontinent was blessed by one such wet phase. It continued its presence till the middle of the month which helped the monsoon onset and also gave bountiful rain. But shortly after this, a strong dry phase entered the subcontinent and maintained its presence till mid-July. This dry phase was likely the strongest one seen over India since the last few years. This was the reason why central and other parts of India witnessed such a big dry spell between June-end and July-end. MJO activity has been weak since July due to which the El Niño has maintained its hold over India's monsoon.

El Niño to strengthen further in the coming months

 

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IMAGE 3: Representation of Sea Surface Temperature anomalies in the Pacific Ocean between 31st August and 6th September 2015. Red colour depicts above normal temperatures and blue colour depicts below normal temperatures. Courtesy: NOAA

 

El Niño is pretty strong now and the Oceanic Nino Index for June-July-August is 1.22°C in the Niño 3.4 region. The Niño 3.4 region (situated at 5°N-5°S, 120°-170°W) is very important as it is that part of the Pacific Ocean whose sea surface temperature anomaly (difference between the observed value and the average value) will reveal if there is an El Niño or not. This means that the average of sea surface temperature between June and August is 1.2°C above normal. This is the third highest value since the year 1950 (we have records from 1950), with the highest being 1.42°C in 1997 (the strongest known El Niño). The latest weekly departure in the Niño 3.4 region is 2.3°C, which suggests a strong departure. The big red patch across the equatorial Pacific Ocean in the above image clearly reflects the strength of El Niño.

El Niño isn't just about warmer sea surface temperatures. The atmospheric circulations too demonstrate changes during it. Weakening or reversal of trade winds is one of the important atmospheric indicators of an El Niño. Gradually, a coupling between the Pacific Ocean and the atmosphere above it is observed and at present we have that! It is because of this coupling that the ocean and the atmosphere are able to influence each other. As per the Bureau of Meteorology, Australia (which independently monitors the Pacific Ocean), these present oceanic and atmospheric indicators are at record levels. El Niño isn't going to end soon! As per the latest advisory from Climate Prediction Centre, there is approximately a 95 per cent chance of it continuing through this winter of the Northern Hemisphere. In fact, these models suggest that El Niño will strengthen around the Northern Hemisphere's winter and it would be a strong one. El Niño's influence will likely be witnessed on India's winter also as it tends to bring warmer than normal winter in India.

 

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IMAGE 4: El Niño's impact during the winter Courtesy: CPC/NCEP

 Monsoon's withdrawal to resume in north India after some rain

The withdrawal of the south-west monsoon commenced on September 4 from western Rajasthan. After that, the monsoon withdrew from some parts of Punjab and Haryana but the process has been stalled since then. IMD has three criteria for declaring the monsoon's withdrawal. Out of them, two state that rainfall must cease in a particular region for (at least) five days and there must be considerable reduction in the moisture content. However, widespread rainfall is expected in the whole of North India and Rajasthan till Wednesday, September 23 due to the combined effect of a low pressure area and a western disturbance. Jammu and Kashmir will get light to moderate rain in this period due to which there will be a possibility of landslides and some water logging in areas like Srinagar. Rainfall amount will be higher on Tuesday, September 22 in North India. Delhi NCR has been severely hit by dengue. As light rain will continue in Delhi till Wednesday and this will be followed by clearing of weather, there will be a possibility of further increase in dengue cases in the remaining days of September if things aren't handled properly.

The monsoon's withdrawal would stay suspended in this week. But, starting from next week (September 28 onwards), the process of monsoon withdrawal will resume in North India as the rain will cease and humidity will considerably fall.

 

Southwest monsoon reaches Kerala

FROM BLOG EDITION - http://www.downtoearth.org.in/content/southwest-monsoon-reaches-kerala

As of now, conditions are favourable for its progress

Progress of southwest monsoon over India (Courtesy: IMD)
 

After a delay of four days, the southwest monsoon finally arrived in Kerala on Friday, June 5. According to a press release by India Meteorological Department (IMD), the southwest monsoon has advanced over the entire south Arabian Sea, some parts of central Arabian Sea, Lakshadweep, Kerala, parts of coastal and south interior Karnataka, Tamil Nadu and some parts of Bay of Bengal.

As of Friday afternoon, the Northern Limit of Monsoon (NLM) or its northern boundary was passing through Mangaluru (Mangalore) and Mysuru (Mysore) in Karnataka and Salem and Cuddalore in Tamil Nadu. The onset of monsoon was delayed in Kerala and southern India by five days even last year. 

This year, the monsoon reached the Andaman and Nicobar Islands region on time, but lost its momentum and lingered around Sri Lanka for more than a week. Thus, it missed both its normal onset date and the date forecast by IMD (May 30). 

It is also running late in the North East and eastern India as the Bay of Bengal branch of the monsoon hasn't made any significant progress when compared to the Arabian Sea branch. 

Despite this delay, India is seeing a "good opening" of the summer monsoon season. From June 1 to 5, rainfall in India was 4 per cent more than normal, thanks to a combination of a western disturbance in the north, pre-monsoon showers in the south, monsoon showers in the Andaman and Nicobar Islands and multiple localised thunderstorms in other parts of India. 

The monsoon has another 118 days (till September 30) to perform in India. Factors such as the state of El Niño Southern Oscillation, Indian Ocean Dipole and frequency of monsoon depressions will influence its performance. 

Arabian Sea low pressure to boost monsoon's progress

Monsoon could regain its lost momentum because of a low pressure system in the Arabian Sea. For the onset of the monsoon in Kerala, it's important for a few atmospheric parameters such as rainfall and wind to achieve threshold values. This low pressure helped build clouds near Kerala which brought widespread rains to the region. Plus, its presence influenced the wind speed and direction and made them favourable. In this way, the low pressure helped pull the monsoon that was stuck over Sri Lanka to southern India. As of the afternoon of June 5, this low pressure system was situated off the west coast of Kerala-Karnataka and had lowest mean sea level pressure of 1004mb. 

Initially, multiple weather models showed that this system would intensify into a tropical cyclone and move parallel to the western coast of India. This could have led to a June 2014-like situation of monsoon's bizarre progress due to Cyclone Nanauk. But as per the present weather model runs, this system would marginally intensify and head almost northwards in a curved path. As of now, the probability of formation of a cyclone like Nanauk is very low. This system would dissipate in the northern Arabian Sea by June 11 and, hence, there is no threat to India. 

To some extent, monsoon is expected to progress faster along the west coast as compared to the interior areas of southern India till June 10. In this period, the western coast (including Mumbai, Pune) will witness rainfall with windy weather due to this system. The Arabian Sea will see rough conditions due to the low pressure. It is expected that the monsoon will arrive in more parts of Karnataka, remaining parts of Tamil Nadu and, possibly, southern parts of Andhra Pradesh by June 8. Mostly dry and hot weather will be witnessed in northern India during this period. 

IMD forecasts deficient monsoon

IMD downgraded the monsoon forecast, from 93 per cent to 88 per cent, dashing hopes of relief from drought in many parts of India. Thus, the forecast is now of deficient rainfall instead of below normal rainfall. (Note that the error range for these estimates is +/- 4 per cent.)

IMD also gave a region-wise forecast in this update. It said that northwest India will receive 85 per cent of LPA (LPA stands for Long Period Average or the average rainfall recorded from 1951 to 2000). Central India will receive 90 per cent of LPA, south peninsula will receive 92 per cent of LPA and northeast India will receive 90 per cent of LPA. All these figures are subject to an error of +/- 8 per cent. 

A decrease of 5 per cent in the rainfall forecast is significant. Monsoon rainfall in India exhibits a large spatial variation and, hence, this 5 per cent decrease can bring a significant decrease in rainfall at many places in India. For example, in 2014, IMD had forecast a rainfall of 94 per cent of LPA for central India. The observed rainfall was 90 per cent of LPA, but the monsoon rainfall in places like Marathwada in Maharashtra was 42 per cent below normal. 

Likewise, rainfall in north-west India was forecast at 85 per cent of LPA. The observed rainfall was 79 per cent of LPA, but a strong rainfall deficiency was seen in the region. Haryana-Chandigarh-Delhi and western Uttar Pradesh recorded 56 per cent below normal rainfall. This is why IMD's downgraded forecast