SWM 2015 Thread

Lets follow South West Monsoon 2015 in this thread. Strictly no other comment should be posted in this thread. With less than 3.5 months away for the onset over Kerala, lets start the build up from now.

july-5-south-west-monsoon

116 thoughts on “SWM 2015 Thread

  1. really a good move!!. common guys let’s use tis section exclusively for southwest monsoon discussions from origin,regional impact & global influence..

  2. Please stick to topic and do not ask unnecessary/repeated questions. If you break the rule of this thread, your comment may be deleted.

  3. Flash News,

    1. NINO 3.4 is likely to increase upto 1C above normal till May 2015. ELNINO or LANINA conditions are completely wiped off.

    2. IOD to remain neutral till May, expected to turn positive by June, will favour SWM 2015, but precipitation forecast still remains below normal in the entire country, except Andaman Islands, NE States, WB, Odisha, Bihar, East UP and Chattisgarh where the SWM rains will be above normal.

    3. Below normal rainfall expected across country during peak summer.

    4. Temperature over Interior parts of our country to be above normal from March to May, the scenario is already seen, many parts reporting 37C already, also in coastal areas temp likely to be normal this summer.

    Note – However from June to Aug temp is likely to be above normal in entire country.
    Also SWM is expected to be near normal as per the current trend, but we need to wait till April to get clear picture.

    https://a.disquscdn.com/uploads/mediaembed/images/1741/1555/original.jpg?w=600&h
    https://a.disquscdn.com/uploads/mediaembed/images/1741/1556/original.jpg?w=600&h
    https://a.disquscdn.com/uploads/mediaembed/images/1741/1557/original.jpg?w=600&h
    https://a.disquscdn.com/uploads/mediaembed/images/1741/1558/original.jpg?w=600&h

  4. For the first time in a decade, India has experienced deficient rainfall in both the main south-west as well as the north-east monsoon seasons.( for 2014 season)
    According to data from the India Meteorological Department (IMD), the country as a whole received an average rainfall of 85.2 mm during October 1 to December 31, 33 per cent below the “normal” long period average of 127.2 mm for this period. South-west monsoon registered an overall rainfall deficit of 12.3 per cent,
    This is the first time since 2004 that rainfall deficiency has been recorded in both south-west and north-east monsoon seasons.
    source: Financial express

  5. Forecast:
    North India: 16th to 24th February 2015
    Due to dual Western Disturbances during 16th to 24th February there would be rainfall over Jammu & Kashmir, Himachal Pradesh, Uttara Khand, Punjab, Haryana, New Delhi, North Rajasthan during the forecast period on multiple days with heavier precipitation during the latter parts of the forecast period. Some of the hilly regions of North India will get snowfall during this period.
    Private weather forecaster: Ashok Patel

  6. generally swm is not a rainy season for tamilnadu .despite the fact, s.east peninsular india tat includes north tn ,s.ap is seeing some increase in rainfall in recent years or a decade during swm which was expressed in few journals n research papers..

    moving deep into it by analysing the precipitation trend time scale of north tn coast & S.AP(above 10N and below 15N) ,it shows the steep increase in swm precipitation over north,n.central tn and coastal s.ap n interior s.ap in recent years

    http://s9.postimg.org/x9ym8z99b/image.jpg http://s22.postimg.org/cxtq96g1d/image.gif http://s4.postimg.org/s7az0ds7h/image.gif

    data courtesy: IRI

  7. All of you Guys,

    This page is specific to SWM forecast, please post relevant to that scenario.

    Shriraam and Vela, your post is just a forecast for next 3 months and for a week.
    Please take care henceforth and be specific to SWM season.

  8. Dear Selvan,

    Thanks for sharing the trend of SWM rainfall in TN, i do have the rainfall pattern increasing trend for Chennai.

    This is from 1901 to 2011. The SWM rainfall has increased from 39 CM to 47 CM per annum.

    The highest amount of rainfall was recorded in 2011 with 769 MM approx.
    The lowest amount of rainfall was recorded in 1920 with under 190 MM, figure not know exactly.

    Graph Attached.

    • Increase in Rainfall pattern during SWM is very good for Chennai, as it reduces as much radiation nights and keeps us easy to manage the season

  9. Urban effects of Chennai on sea breeze induced convection and precipitation

    Doppler radar derived wind speed and direction profiles showed a well developed sea breeze circulation over the Chennai, India region on 28 June, 2003. Rainfall totals in excess of 100 mm resulted from convection along the sea breeze front. Inland propagation of the sea breeze front was observed in radar reflectivity imagery. High-resolution MM5 simulations were used to investi-gate the influence of Chennai urban land use on sea breeze initiated convection and precipitation.

    A comparison of observed and simulated 10 m wind speed and direction over Chennai showed that the model was able to simulate the timing and strength of the sea breeze. Urban effects are shown to increase the near surface air temperature over Chennai by 3.0 K during the early morning hours. The larger surface temperature gradient along the coast due to urban effects increased onshore flow by 4.0m s−1. Model sensitivity study revealed that precipitation totals were enhanced by 25 mm over a large region 150 km west of Chennai due to urban effects. Deficiency in model physics related to night-time forecasts are addressed…..

    http://www.ias.ac.in/jess/dec2008/jess175.pdf

  10. A study of the relationship of the southwest and the northeast monsoon season rainfalls over TamilNadu has suggested a tendency for an excess or deficit southwest monsoon rainfall to be associated with the opposite tendency in the subsequent northeast monsoon rainfall.

    Correlation analysis, which revealed a negative correlation, showed that

    • The rainfall distribution during the southwest and the northeast monsoons are not independent.

    • The magnitude of the deviation in the southwest monsoon is directly related to the magnitude of the opposite deviation in the northeast monsoon rainfall. From the foregoing, it thus appears that, the observed southwest monsoon rainfall over Tamil Nadu can be used to provide a forecast of the behavior of the following northeast monsoon season.

  11. Selvan,

    As you have explained about 200 HPA winds Upper Tropospheric Flow, i have looked at it month wise in CPC website.
    Based on the changes of wind direction at this level, we can predict the onset of SWM?
    We usually predict onset of monsoon based on 850 HPA wind direction and its strength above 30 knots, but 200 HPA level winds will react opposite during SWM season i believe.

    Till May the 200 HPA winds direction upto 25N is West to East, whereas by end of May or June beginning the wind direction at this level upto 25N changes to East to West, so that is the time we might be having the SWM onset, is it not?

    Another point is that till April month the wind direction is from south to north over Andamans, but in May the wind changes to perfect East to West direction, that is when the SWM onset happens in Andaman Islands where the monsoon’s first striking place in India.

    Hope this can tell us the onset date of SWM when we track it on daily basis from the beginning of May month.

    Correct me if i am wrong.

    http://www.cpc.ncep.noaa.gov/products/precip/CWlink/climatology/Wind-200.shtml

    • Tropical easterly jets at upper level is one of the characteristic feature of swm.. but it’s complete establishment (placing itself around Tibetan plateau and adjoining latitude) happens after june. So by that time swm onset might have happened in kerala coast n way early in andaman islands. so It won’t hold a key in predicting the onset factor.. as far as bay branch onset is concerned, watchout for bay cyclone and Cross equatorial flow .. low level somalian jet for onset over kerala coast .. sst decreasing sharply along Somalian waters after touching a peak sst in may, decreasing south indian ocean sst & developing mascarene high are the key factors deciding the Arabian sea branch of swm.

      • Perfect selvan, it is exactly opposite now in Indian Ocean as you have said, the Northern Part is cooler and the Southern Part is hotter, during May it will vise-versa.

        i know we have to track low level jets at 850 HPA, but thought of following 200 HPA as well, lets follow the somalian jet and mascarene highs from now on, if possible i will take a pic of MSLP and SST of both part of Indian Oceans.

      • Sst increasing over north indian ocean may attract the itcz line during april end.. by tat time sst shld start go down in s.indian ocean or else it could cause the delay in northerly movement of itcz line and so monsoon gets delayed.

    • System formation in bob during spring happens When upper level divergence from a high pressure area strengthens in bay which normally happens due to wave activity..

  12. Why are south-west monsoons less rainy in Chennai?
    The Eastern Ghats are lower in altitude than the western ghats. This makes the places lying in the Eastern Ghats fall in the rain shadow region. This makes the monsoon rains lose its moisture on the western slopes of the Western Ghats and the rest of the plateau and the eastern ghats
    gets scanty rainfall.
    Because of this Tamil Nadu (Chennai) gets less rain fall during South West Monsoon.

    • Normal rainfall for June is 76 mm. Three of the last Five years we crossed 100 mm. So definitely we can get evening TS in June

      • after the poor show last year, we should have excess rainfall from this year’s S.W.M as well as N.E.M, near normal or Normal rainfall can’t suffice our needs, I hope and pray for that.

      • if you are talking about Chennai alone, then I would like to share that SWM and NEM was normal. SWM (excess of 16%) and NEM (deficit of 12%)
        Deficit of 12% is not considered a failure.

      • not contesting the official values. but considering our Poor / near normal NEM for the consecutive 4 years, I think we should have excess rainfall this year, we the Chennai city and near by dists. are growing by year and year in Population, and area, and the rainfall which was enough in 80’s and 90’s , can’t be enough today

      • how can you expect rains to increase based on population growth? Our govt should take adequate measures to build reservoirs to hold more rain water for the growing population.

      • yes, for one or other reason we kill nature, and it repays us in a severe manner, can we get at least this current qty, say after 25 or 30 years?

      • A lake is being built in Tiruvallore dt, and it is initial stage, also there is a talk, that, to full fill Chennai water needs, , connecting Mettur dam with Chennai reservoirs like Veeranam project , but the proposal is in initial stage

  13. SWM has been becoming one of the important for tamilnadu especially interiors.
    70% of interiors benefitting from SWM most probably West and NW tamilnadu like krishnagiri, dharmapuri, salem, erode, Coimbatore dist getting much of rains in SWM than NEM.
    Last year there is not even more than 50mm in west and NW tamilnadu in NEM but 700-800mm occured in SWM mainly salem, erode, namakkal, coimbatore, dharmapuri, krishnagiri dist.
    Just 15 days more for western ghats to have TS and some LWD will give plenty of showers over interiors.

  14. partha sir
    you told max rains from swm in chennai has occurred in 2011 but what about June 13 1996 cyclone which gave nearly 70cm to chennai in three days? it was swm season

  15. kea,
    sorry for posting this here..
    pls can u give me the account details to open it again..dont delete this comment as sooon as u give becoz i am going to school..
    this time i will not forgot the password..pls
    or
    i hav to send in mail????

  16. If coming summer is severe (above normal), then the rainfall also will be above average during SWM. As global temperature is shooting up, old rainfall patterns may serve as a guidance and can’t be relied upon.

  17. reason for the poor performance of 2014 swm in june was because of irregular position and lack of strength of the monsoon factors.. mr .ramanan highlighted ” 2014 june ,neither the monsoon trough nor the mascarane high wasn’t seen normal in the month of june.. one or the other fell out of line leading to poor june in terms of rainfall

  18. Has there been an El Niño over the past few months or not?

    Some Californians would like to think their brief but potent bouts of drought-busting storms were brought by what has been a marginal ocean warming of the tropical Pacific.

    But San Francisco still just had its driest January on record.

    And while some global weather patterns have been similar to what would be expected during an El Niño, the main characters of the phenomenon have not really set in.

    This has baffled scientists since computer models had consistently predicted a major El Niño warming event would develop in 2014.

    Australia’s Bureau of Meteorology says that temperatures across the Pacific have recently returned to a “neutral” level between what would be considered an El Niño and a La Niña.

    But the Japan Meteorological Agency says the atmospheric jury is still out.

    It predicts there is a 50 percent chance that El Niño will re-emerge during the Northern Hemisphere summer.

  19. Early prospect regarding SWM-2015 forecast:
    SWM-2015 may progress normal (based on 1st point) but get delayed/with weak intensity (based on 2nd point) if we understand the following 2 points on broader prospective:

    1. Unlike 2014 (no spring at all in USA in 2014) in 2015 spring-fever starting on high note in regular time. Parts of Europe/Eurasia already in spring fever (in 2014 spring fever is weak)

    The good normal spring fever in USA/Europe/Eurasia will reflect on Tibetan monsoonal low (one of the pull engine of SWM-push-pull train), which makes SWM-train to start on normal time line around June 1 (+/-4 days).

    However

    2. If we look into SST & sub-surface SST (even BoM/NOAA warning 50-60% Elnino staying by the time of mid-year that is June in 2015), it looks central pacific again on warming trend. Bur if we consider powerful killer of Elnino i.e. SPRING-barrier, this Elnino-probability may not survive by end of June (If not mid-July).

    The ENSO-factor is one of the main component (apart from mascarene high, IOD) of push-engine of SWM. This mild Elnino factor coupled with -ve IOD will make weak SWM-conditions over major parts of India till June-end. However active/vigorous SWM-2015 conditions will start from starting the JULY month.

    1. normal spring: http://www.weather.com/weather/tenday/l/Hershey+PA+USPA0710:1:US
    2. SST: http://www.bom.gov.au/climate/enso/#tabs=Sea-surface

  20. imd outlook: above normal precipitation expected for most parts of tamilnadu & kerala during march,april,may.. to be more specific, the positive anomalies of precipitation were seen high during the month of may tat makes it difficult to say what is affecting the southern parts.. it could be very unseasonal thunderstorms or early outbreak of swm or even a may tropical cylone

    march-april-may preciptation forecast

  21. CMIP5 MODEL REANALYSIS results shows relation between swm precipitaion and east pacific warming is quite effective in last few decades. interesting part is that the negative correlation between south asian summer monsoon precipitation and SSTAs in the eastern equatorial Pacific will weaken and even reverse to a positive one in the period 2070–2096

  22. ELNINO development during Onset of SWM.

    2015 ELNINO would be only the 06th time in the past 65 years that develops during or before the onset of SWM.

    Previously it was during 1957, 1972, 1987, 1997 & 2002.

    If ELNINO sets in during Northern Hemisphere summer or before onset of SWM season, then the effect is Negative in terms of Rainfall.

    SWM rainfall performance all over India during these 5 years.
    1957 – Actual 898 MM, normal rainfall registered.
    1972 – Actual 697.4 MM, below normal.
    1987 – Actual 774.6 MM, below normal.
    1997 – Actual 927.3 MM, above normal.
    2002 – Actual 737.3 MM, below normal.

    During these ELNINO development before onset of SWM, the most affected regions in India during SWM are

    North West India, South Peninsula and Central India. These regions get below or near normal rainfall.

    Regional Wise Data
    North West India
    1957 – 753 MM, excess
    1972 – 412 MM, deficit
    1987 – 371 MM, deficit
    1997 – 660 MM, normal
    2002 – 434 MM, deficit

    Central India
    1957 – 866 MM, below normal
    1972 – 754 MM, deficit
    1987 – 683 MM, deficit
    1997 – 994 MM, normal
    2002 – 829 MM, below normal

    NE India
    1957 – 1250 MM, normal
    1972 – 1106 MM, below normal
    1987 – 1684 MM, excess
    1997 – 1473 MM, above normal
    2002 – 1353 MM, normal

    South India
    1957 – 732 MM, normal
    1972 – 573 MM, deficit
    1987 – 541 MM, below normal
    1997 – 728 MM, normal
    2002 – 506 MM, deficit

  23. 29th March Models show Elnino and negative IOD..this generally leads to a sluggish SWM in June.
    It also forecasts Elnino and positive IOD during our NEM period which could see a bountiful NEM ( we should take it with a pinch of salt as it is too long term)

  24. ELNINO & SWM Relationship.

    ELNINO and SWM has met 14 times since 1951. Out of these 14 times, 6 times SWM were successful and 8 times failed.
    ELNINO is not the only relationship have to be seen for failure, but IOD is also the another factor which can influence the South West Monsoon Rainfall.

    So we need to take ENSO and IOD factors to compare it with SWM rainfall success rate.

    SWM failed in following years:
    1951, 1965, 1972, 1982, 1987, 2002, 2004, 2009.

    In the above 8 years
    ELNINO with Neutral IOD combo was with 5 years (1951, 1965, 2002, 2004 & 2009)
    ELNINO with Positive IOD combo was with 3 years.(1972, 1982, 1987).

    SWM was successful in following years:
    1953, 1957, 1963, 1969, 1991 & 1997.
    In these 6 years ELNINO with Neutral IOD combo was with 3 years (1953, 1957, 1969).
    ELNINO with Positive IOD combe was with 3 years (1969, 1991 & 1997).

    1. Lets take Positive IOD years first:
    There have 3 successful and 3 failures. When it fails and When it is successful?

    During ELNINO Years, when IOD becomes positive before SWM season then it fails to trigger normal rainfall. If the Positive IOD develops after the onset by June or July then it helps the SWM to become normal to excess.

    In 1972 & 1982 positive IOD developed before May month itself and in 1987 the Positive IOD developed in late August, hence it could not trigger precipitation. Whereas in 1969, 1991 & 1997 the Positive IOD developed in July, so it could trigger more rainfall and season ended in Normal.

    2. Now Lets see the Neutral IOD with ELNINO:
    There have been 8 years with this combo, 1951, 1953, 1957, 1965, 1969, 2002, 2004 & 2009.
    SWM could succeed in 1953 1957 & 1969. 5 times failed 1951, 1965, 2002, 2004 & 2009.

    Successful Years – In 1953 & 1969 ELNINO developed later in August, hence SWM could manage to end in Normal mode, whereas 1957 was exceptional, even though ELNINO were strong enough and IOD Neutral it could manage to end in normal mode. Failures does not need an explanations since ELNINO impact is clear.

    Finally to summarise:

    ELNINO might impact SWM to some extent, whereas the IOD can support the SWM to finish it in Normal style.
    SWM will be successful during ELNINO years when Positive IOD develops after SWM onset and before first half of July.

    Presently the IOD is neutral, it should become Positive before July to get SWM successful.

    ELNINO with Neutral IOD also has some normal years, but it is unpredictable. If we get the support of MJO, then we can overcome the shortfall.

    Note – ELNINO can disturb SWM, but Local Factors like IOD plays major role.

  25. Updated – SWM and NEM Rainfall in Chennai during ELNINO coupled with IOD Years.

    1. South West Monsoon:

    During 14 ELNINO Years, SWM failed 9 times and succeeded 5 times.

    We all know SWM will fail during ELNINO years; it has succeeded 5 times 1957, 1965, 1982, 1991 & 2004.

    A. In 1957 & 1965 ELNINO developed before March itself,hence SWM was not affected much. In 1982, 1991 & 2004
    ELNINO were weak and ENSO values around 0.7 and 0.8 hence not affected the SWM rainfall in Chennai.

    B. SWM Failed in 1951, 1953, 1969, 1972, 1987, 1997, 2002 & 2009.
    Except 1972, 1987 & 1997, all other years ELNINO was at developing stage like 2014, these unsettled condition impacted SWM performance. These years there was a strong ELNINO developed before May itself, even though 1972 was positive IOD year could not help SWM.

    2. North East Monsoon:

    During 14 ELNINO years, NEM failed 8 times and succeeded 6 times.

    A. The success was in 1969, 1972, 1987, 1997, 2002 & 2009. ELNINO were strong. All years IOD & ELNINO were settled
    by August or September and continued with same value till the onset of NEM.

    B. The failure years 1951, 1953, 1957, 1963, 1965, 1982, 1991 & 2004. These years IOD were inconsistent and Neutral during August and September, hence NEM failed. Except 1982 all other years IOD was neutral. In 1982 ELNINO formed in July itself.

    To Summarise SWM:

    1. If ELNINO developed before SWM and Positive IODdevelops after onset then SWM will succeed
    (E.G. 1963, 1982, 1991), Positive IOD should set in between Jun-July,not early or late, even if it sets in August
    will derail SWM performance, (E.G.1987).

    2. If ELNINO developing during SWM then Positive IOD developed after onset can support SWM.
    3. If ELNINO and Positive IOD both developed before onset of SWM, then SWM will fail.

    To Summarise NEM:

    1. If ELNINO & Positive IOD formed before August and continued till NEM, then NEM does not succeed.
    (E.G. 1963, 1982 & 1991)
    2. If ELNINO formed earlier and Positive IOD gets settled by September, then we will get good NEM.
    (E.G. 1972, 1987, 1997 & 2002).
    3. If ELNINO formed in August and settled in September, then even if IOD is neutral till September, then also NEM successful. (E.G.1969 & 2009).

  26. Flash News,

    Jamstec Forecast

    Below Normal Jun to Aug Rainfall,
    Excess Rainfall during NEM 2015 over TN likely

    1. SWM likely to be below normal across the country.
    1a. Kerala, Coastal KTK, Madhya Pradesh, Bihar, Jharkhand, Odisha, West Bengal, NE States likely to get normal to above normal rainfall.
    1b. Tamilnadu, Andhra Pradesh, Interior KTK, Maharashtra, Goa, Gujarat, Rajasthan, Punjab, Haryana, Himachal Pradesh will get below normal rainfall.

    2. IOD & IO Subtropical Dipole Index likely to remain neutral during entire 2015. This may not favour SWM rainfall.

    3. ELNINO likely to emerge by first half of May 2015.

    4. Excess Rainfall during NEM 2015, precipitation expected to be above normal during NEM in Tamilnadu.

  27. ELNINO during SWM Onset and Chennai Rainfall in SWM and NEM season.

    As i said below, 2015 is 07th time since 1951 that ELNINO setting in during SWM onset.
    Lets see the impact over Chennai Rainfall during June to September and October to December.

    Even though Positive IOD was present in 1972, 1987 and 1991 SWM was Below Normal to Normal these years, since Positive IOD was emerging before the onset that is before May, but in 1997 has given more quantum of rainfall for entire country, whereas for Chennai it was contrary, in 1997 we have registered below normal rainfall, during 1991 alone we have registered Normal rainfall.

    Overall Chennai is getting impacted by ELNINO directly even though we had Positive IOD years in the past.

    The 1997 situation is once again repeated this year, hence Chennai is likely to get below normal to normal rainfall.

    1957 – Actual 402MM, Normal
    1972 – Actual 328MM, Below Normal, Positive IOD
    1987 – Actual 278MM, Below Normal, Positive IOD
    1991 – Actual 405MM, Normal, Positive IOD
    1997 – Actual 282MM, Below Normal, Positive IOD
    2002 – Actual 351MM, Below Normal, Neutral IOD

  28. How SWM was successful in 1997 even when the Strongest ELNINO of history emerged.

    In 1997, the central to east pacific was hotter and the above normal sst was
    prevailing. Since the the descending air flow was shifted away from the Indian subcontinent the monsoon was unaffected.

    During the 2002 event, however, the warming was concentrated in the central Pacific. With the warming in the middle of the Pacific, the descending air flow reached much farther west, closer to the Indian subcontinent. The result was drought.

    Hence the heating portion of NINO regions are important.

    ELNINO values alone not the deciding factor for influencing SWM.

    So far the above normal SST was prevailing across the Pacific from East to West, but latest SST anomaly suggests that the SST will decrease over West Pacific, hence the air will not descend over Indian Ocean, this is good news…

    https://www.climate.gov/news-features/featured-images/will-el-ni%C3%B1o-dry-out-indian-monsoon-well-it%E2%80%99s-complicated

  29. SWM onset

    ————-

    For the first time, both GFS and ECMWF are agreeing on the same onset date. Both the models are expecting monsoon onset by 30th/31st as expected earlier. The onset this time from ECMWF’s perspective is going to be bountiful for Kerala and parts of Coastal Karnataka, but a rather tame onset for other coastal areas and in comparison with other onsets. This is because an UAC is going to form off Kerala coast embedded in an off-shore trough. This will enhance rains in Kerala making the onset ordinary from sub-par for those regions.

    We could see 1 or 2 places notch 10 cm+ in 24 hrs in the days of the onset in Kerala due to the UAC. It is going to help monsoonal flow, but if it intensifies to a cyclone and moves north, monsoon rains will be delayed even more for west coast even though it would pull the SWM ARB current northwards.

    South Karnataka could see decent rains around the time of onset. From central coastal KTK, the rains start to become very tame compared to other SWM onsets. A below normal June is expected in general with an above normal July. Let’s track the SWM onset with it’s northern limit day by day.

    Here is the ECMWF wind chart indicating onset by 30th into southern Kerala helped by upper air trough.

    To conclude, pre monsoon showers from 28th, patchy heavy rains in Kerala and Central to south coastal KTK from 30th/31st. North coastal KTK and Goa will have to wait for heavier rains. But could face some moderate showers

  30. Pre monsoon showers likely pickup in Kerala from 28th. UAC development will enhance rainfall and bring in moist air from SLLJ to Kerala coast which should trigger onset when I’m there hopefully!

  31. My LRF SWM 2015

    I was always saying that there is a difference between summer & winter ELNINO.
    We had 14 ELNINO years in the past since 1950, but only few of them were summer ELNINO’s.

    2015 ELNINO has been summer ELNINO. If ELNINO emerged in summer along with that Positive IOD, then we should get normal SWM. However IOD should become Positive before August, otherwise it will be too late.

    Summer ELNINO 1972, 1982, 1991, 1997, 2002, 2004, 2009 & 2015.

    1972 – Positive IOD developed before May. Deficit SWM
    1982 – Positive IOD. developed before May. Deficit SWM
    1991 – Positive IOD. developed before May. Below Normal SWM.
    1997 – Positive IOD in June. Excess SWM
    2002 – Positive IOD in August end. Deficit SWM
    2004 – Negative IOD. Deficit SWM. Conditions like 2014.
    2009 – Neutral IOD but ELNINO emerged late in August. Deficit

    Another factor is ENSO values can show positive and it will be declared ELNINO, but which part of Pacific has above normal SST, that has to be checked.

    Find the link below, how SWM had overcome 1997 ELNINO and how it failed in 2002. Even though you can say that Positive IOD developed on time in 1997 and was late in 2002, it was influenced by Pacific ENSO.

    Still Positive IOD has to emerge between May and July during Summer ELNINO years for successful SWM.

    Since West Pacific SST was near Normal in 1997, Positive IOD emerged. In 2002 West to East Pacific SST was above normal and East Pacific was hotter than West hence ELNINO formed, since West Pacific SST was above normal, Positive IOD could develop only by August. This is why SWM failed.

    This time in 2015, ELNINO declared in May, Positive IOD expected in a weeks time, SST over West Pacific cooling off.

    Almost everytime NW India is affected during ELNINO years, irrespective of Positive IOD, once again NW India might get affected.

    Central and NE India will survive, in some of the ELNINO years they got excess rainfall too.

    North and South India will be near normal this time. Except Tamilnadu, will surely face deficit.

    Hence SWM will succeed this year if strong Positive IOD emerges and should remain strong or if increase in values, then 2015 will become a repeat of 1997. If Positive not strong or does not sustain then SWM will fail in 2015.

    If IOD remains Neutral or Inconsistently Positive or Weakly Positive then Chennai has every chance that it will get Normal rainfall during this SWM season.

    https://www.climate.gov/news-f

  32. Observation on SWM 2015 and Tropical Waves this Season.

    When a monsoon season has more Kelvin or Rossby Waves, then monsoon in that season will fail. The upcoming SWM season also likely to see frequent Rossby and Kelvin Waves and MJO might not be frequent as it was in previous times.

    The reason is ELNINO. this phenomenon suppresses moisture in Indian Ocean in the long run and the Pacific Ocean keeps MJO with itself for most of the time.

    Kelvin Wave likely to help monsoon to some extent but the reflective of Rossby might not. This Rossby wave will help the Upper Level moisture to get developed, this will bring occassional thunder storms and suppresses the lower level moisture and the lower level steering winds will not get the required moisture for monsoonal rains.

    This is when the Positive IOD will help the lower level winds to get moisture during SWM. This time we might get Positive IOD but not going to sustain and will be back to Neutral. The unsettled IOD during this season might fail the SWM 2015.

    There is an advantage for Chennai. During ELNINO when there is no Positive IOD, then those years Chennai got Normal Rainfall during June to September, since upper level gets more active, by nature Chennai gets TS during this season, it helps Chennai to get normal rainfall during SWM season, this is due to failure of Positive IOD establishment.

    Hence we will see more Rossby Wave and Less MJO this season.
    Also IMD has pulled the right string and Chennai might get normal rainfall during SWM. This is just my assessment based on some logic, correct me if i am wrong…

  33. Flash…deluge alert for Chennai in 2nd half of July when MJO enters IO:

    The much awaited wide-spread high energetic VS-TS (might be hybrid) will be awaiting for whole Chennai when MJO entering IO at phases 1/2/3.

    This wide-spread VS-TS might be the part of oceanic tropical convergence zone (OTCZ, supports both Arabian & BOB SWM wings) as part of monsoon intra-seasonal oscillation (MISO)

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