Wednesday, August 01, 2012

Parameters that will influence the August Rainfall .. and "Drought" seems to be certain !!.. 

Parameters that will influence the August Rainfall

Parameters that will influence the August Rainfall:
The main and holding parameter is the location of the Monsoon Axis (Trough). Depending on the alighnment of this axis, the following vary and fluctuate: 

1. Systems form The Bay:-
It is the depressions and cyclonic circulations/storms that play an important role in the distribution of rainfall over the Sub-Continent.
This year, we have had BB1 and BB2 and in reality BB1 was as good as a non starter.
It is, therefore, of interest to know to what extent the absence of these synoptic systems causes deficient rainfall during the individual monsoon months. This aspect has been examined by computing the average rainfall of the different meteorological subdivisions of the Indian plains north of 15 degrees N lat. for monsoon months that were free from depressions and cyclonic storms. 

During the period 1891-1980, there have been 25, 13, 7, and 4 occasions of June, July, Aug., and Sept., respectively, when no depressions or cyclonic storms moved through the Indian land area.

A study also shows that the absence of monsoon depressions and cyclonic storms is not the main factor that causes deficient rainfall and consequent drought conditions in India.

Another study had shown that the occurrence of moderate to heavy rainfall mainly depends upon their frequency, life span, track followed and origin of these disturbances provided there are no inhibiting meteorological factors like `break' monsoon situations.

Initially, no system from the Bay is expected in the first week/10 days of August. A system BB3, is possible later. (See below)

Indicator for this August: Overall Favourable. 

2. MJO:-
The MJO wave shows weakness initially till the 12th at least, as it travels Eastwards. Currently it is still "within the weak circle".
While moving eastwards, it can trigger more typhoons in the West Pacific Ocean, and send a couple of more "pulses" into the Bay..around 12th/13th? 
After the 15th of August, forecasts say the MJO picks up again in the Indian Seas.

Indicator for this August: Favourable for 2/3 systems from the Bay in the second half.

3. ENSO:-
The ENSO conditions are likely to run through the Neutral conditions throughout August. As El-Nino is just on the "threshold" it is not expected to establish itself in August.
For most of month of July, the El Niño-Southern Oscillation (ENSO) demonstrated neutral values. The end of July, saw Niño3.4 at just threshold value. Nino 3 is the only sector above El_Nino threshold. 
Suspicion that the episode now developing in the Central Pacific may not be a normal El Niño and instead could be its variant El Niño Modokai (pseudo-El Niño). However, the latter can be confirmed as an episode only in September. 

During an El Niño Modokai episode, seasonally, it is the North-West region of India that usually bear the brunt of drought, followed distantly by peninsular or South India. Interestingly, this is how exactly the deficiency pattern is panning out this monsoon season.
Tropical cyclones formed during the year prior to the El-Nino years [El-Nino (-1) year] are seen crossing mostly (in 79% of cases) either north of 17 degrees N or recurving in northeastward direction. In other years this kind of behavior is not generally observed. 

Indicator for August: Getting Un favourable by the 3rd week of August.

4. SOI
The SOI is showing the latest as +0.9.

Indicator for August: Favourable for just about Normal rains.

4. SST:-
A preliminary study of synoptic sea surface temperature (SST) measurements made by ships plying over the north Indian Ocean has revealed the existence of an interesting ocean-atmosphere interaction. Large-scale monsoon failures over India during 1965 and 1966 caused an increase in SST in the Arabian Sea and Bay of Bengal. The warm seas may have been the cause of a persistent anticyclone that formed in the upper troposphere over the Indian seas immediately after the 1966 monsoon and persisted there until the monsoon of 1967, which was a normal monsoon. 

This is one parameter linked to the IOD and the IOD is predicted to be neutral..or mildly positive at +0.18...SST in the Arabian Seas are high presently, and high in the West/SW of the Bay...

Intensity of upwelling over the coastal waters of Somalia and Arabia (which is apparently regulated by the strength of the monsoon) is a factor with a major role in this interaction. These large-scale changes are found to affect the cyclone tracks also. This mechanism could, therefore, be the cause of the 3-yr oscillation in subtropical westerlies /tropical easterlies over south Asia, Indian monsoon rainfall, and tracks of the post monsoon severe cyclones of the Bay of Bengal observed during the decade 1965-1974 and reported by Joseph (1975, 1976).

Indicator for August: Again, just favourable for the Monsoon to "survive" not really "revive"

5. Jet Streams:-
During 1972, a year of large-scale drought in the Indian summer monsoon rainfall, the mean u-field at 150 mb shows a weaker than normal tropical easterly jet stream over south Asia and a stronger than normal subtropical westerly jet stream over Australia; the mean v-field shows that the cross-equatorial northerlies are weaker and displaced eastward by similar to 20 degrees long.

The two years (1970 and 1975) of highest monsoon rainfall for India of the decade 1970-1979 were compared with the two years (1972 and 1979) of lowest monsoon rainfall in the strength of the subtropical jet stream (STJ) over Australia as seen from an analysis of monthly mean u-fields of July and Aug. It is seen that, during the poor rainfall years, the STJ is similar to 20% stronger than in the good monsoon years.

It will be interesting if we find any similar occurrences this year. As yet the Jet Streams over Australia are much stronger. Easterly Jet Streams in the upper Himalayan regions are also very strong. Could possibly lead to rains in Northern Pakistan, possibly if they slide down a bit.

Indicator for August: Negative for good flow.

Forecast for August:

If we see and study all the factors, it’s quite puzzling and not leaning towards any one side..its something like "yes and No'. But that does not answer our question.

To summarise: 
The negative indicators may just about disrupt an ongoing monsoon process, but the the positive parameters, which may ensue later, may be able to at least keep up with the normal tempo. 
Initially, the Axis mves North, and possibly brings about a "break Monsoon" condition in the 1st week. Excessive rains in the Hill states and Upper UP. But east and west off shore trough becomes weak.
A couple of systems are possible from the Bay after the 12th, due to the MJO moving eastwards into the S.China Sea. 
An eastward propagation may lead the MJO into a weak phase during the first half of the month. The MJO phase, seeing its periodical wave, stands a chance of strenghtening after 15th August.
By end Augaust, El-Nino could rear its head, but meekly. 

Consequently, NW India, Interior Southern Peninsula and Gujarat would get deficit rains in the Month of August. 
Central India and NE would be normal, while West coast, Karnataka and Konkan could end up with slightly deficit rains during the month. 

Northern State of UP and the Himalayan Foothills region may get excessive rains, possibly leading to flooding downstream into Bihar.

Over all, on the ALL India Level, August can just about get the normal August quota. This means, the carry forward deficiency could end up around -17% to-21% level..

Taken from

Why less rains along W,S-W coast of India?

Mascarene High near Mauritius island [Normal position: 30 Deg South / 55 Deg East]which is considered to be the POWER HOUSE of SWM is NOT favorable this time and lies close to 80 Deg East. This inhibits the cross equatorial flow to hit at Kerala, Karnataka, Konkan,Goa & Maharashtra coast. Further the 100 hPa easterly wind normally expected at Chennai latitude [13 Deg North] is not pronounced this time. This may be one among the reasons for the lack of rain in those regions on All India SWM Rainfall Toppers from 01.06.12 to 10.07.12
Special Monsoon Watch for August.. "Drought Alert" .. 
#chennai - NO signs of rain for the past 2 days. Thin high cloud covered day with Humid & Hot.

#chennai , N.Tamilnadu and S.Andhra may get an isolated T.shower tomorrow after 4pm.. Because Vertical.V is high.. 
For next 24hrs, very less rains forecast over Most of India, except over N-E states and entire Himalayan foothills..

By evening of 3-Aug, Heavy & widespread rains will start over entire E,E-central India due to upcoming Circulation..

Showers over E.India on 3-Aug, evening is expected to move W,W-N-W till 6/7-Aug.. and vanish over N.Madhyapradesh..

Showers may push into Haryana, Punjab and #Delhi on 4,5-Aug.

From 4/5-Aug, Showers along S-W coast is expected to be moderate & widespread along Maharastra & Karnataka coast..

Very less or NO rains forecast for #Kerala till 6-Aug.. !!
RT @rushikeshgk: @weatherofindia @shanpati incorrect, light drizzles experienced all throughout in South Bombay 
Surprise!.. a UAC may pop along S.Andhra, #chennai coast on 8-Aug !!
Today, 2 weak UAC can be seen, 1 along N.Maharastra coast and another over Orissa & S.chatisgarh ..

Next UAC along Orissa coast is expected to pop on 3-Aug..

The upcoming UAC along Orissa coast on 3-Aug will travel West into N-central.Maharastra on 4/5-Aug..

By 5-Aug, the next UAC is expected to vanish over N-W.Maharastra & S,S-W.Madhyapradesh.
Today the monsoon axis is more along Himalayan foothills ! and will be till 3-Aug.

By 4-Aug, the monsoon axis is expected to shift to it's normal position.

And on 4-Aug, a circulation expected over S-E.Uttarpradesh, Jharkand..

A LOW pressure is also expected over S.Bengal on 4-Aug..

Today, heavy rains all along Himalayan foothills, Nepal, Uttarakand and into Himachal can be seen .. 
Today the offshore trough along S-W coast persists from Maharastra coast to N.Kerala coast..

The present weak offshore trough along S-W coast will persist in same way till 7-Aug

Today, low level circulation can be seen over S-central.Uttarpradesh.. and it's extension can be seen upto S.Bengal..

The present low level circulation over Uttarpradesh will vanish in another 12hrs.
RT @shanpati: @weatherofindia not a single drop of rain today in #Mumbai ... Majje ki baat hai ki ajj chand bhi nikal aya hai! (10:03pm)

Special Monsoon Watch for August:-
Deviating from the routine, This additional MW has become necessary due to the SW Monsoon's poor performance in June and July 2012.

Seasonal Rainfall from 1st June - 31st July 2012;
Indian Regions:
NE  -10%  NW  -36%  Central  -15%   South Peninsula  -23%
India: -19%.
Analysis of India as a whole shows: 89% of India is in the deficient range (deficient range is -1% and above. Not -20% as taken by IMD.).The best performance yet is Sikkim and adjoining W.Bengal at +16%.
11% are in the normal range. (Normal means actually in the positve range).
Most deficient is Saurashtra and Kutch at -79% followed by Punjab at -67%.

What has gone wrong this year?

The reasons for deficient rainfall could be attributed to the late arrival and subsequent weak monsoon conditions over the country, the axis of monsoon trough remaining shifted to the north of its normal position, and non-occurrence of low pressure areas (or land lows) across the country.

Also, uneven spatial and temporal variability within the season may result in deficits in the seasonal mean all-India rainfall (AIR) which can have profound social and economical consequences.

What actually plays an important part for a good Monsoon?

The years 1965 and 1972 were years of severe drought over India and its surrounding area. The dynamical and thermal features of these seasons are contrasted with those of the normal monsoon. The main local abnormality during drought years is the shift of the monsoon trough northwards and the development of anticyclones over central India in the lower troposphere.

Drought years are associated with lower chances of low pressure areas to intensity into depressions, less westward movement, more horizontal extent, intense pressure departure from normal in comparison with flood years. However, more monsoon disturbances tilt significantly during flood years. The rainfall associated with these disturbances is highly variable and does not depend on the intensity, horizontal and vertical extent of the individual system. More number of lows intensify into depressions during strong monsoon conditions compared to those of weak monsoon conditions. Lows and depressions during strong monsoons have more westward movement and longer life period. Generally, very few lows form during break monsoon and none of them intensify into depression.
Hence, the presence of mid-tropospheric heating during strong and weak monsoons is essential for the formation of depression.

Parameters that will influence the August Rainfall:
The main and holding parameter is the location of the Monsoon Axis (Trough). Depending on the alighnment of this axis, the following vary and fluctuate:

Read the full article and the expectations for August on Vagaries.
Compiled by Rajesh and Rajan.
RT @nikhiljoshi1: Rain has really taken a toll this year. August now still no roar from the rain which lashes Mumbai

RT @iamjay_jay: #MyAugustWish Rain Gods, please let it rain.. #kochi #kerala

RT @madhuharidas: No rain in kerala. imminent power cuts expected.  

RT @nihar13: Raining badly in Pune. 19:57. Wind around 60 kmph. Raining since yesterday non-stop. Rivers almost full in 2 days! 31-jul

RT @rajugana: @weatherofindia Bangalore 11.00am, Sunny, hot & humid, no rain for the past two days. (31-July, late update)