UAC weakens and moves north, However Chennai to get Rains

The UAC has moved north and got weakened all these activity happened suddenly in the evening and this shift means the heavy rains expected in Chennai will not be as heavy as envisaged previously. There is good chance for moderate rains in Chennai. The weakened UAC seen below –

weak UAC

UAC expected to move South / East
The UAC will not fizzle out as expected by many including ECMWF. Instead it detaches from the steering of the HPA in BoB and is steered back to East / South AP by tomorrow night under the influence of North westerly – Southerly direction.

Chennai Rains : Its been one of the tricky system. Everyone had forecasted rains including IMD, other blogs, ECMWF for tomorrow. Now most of them dont expect the UAC to be steerdown back to South AP / North TN coast and therby taken the rains forecasted in Chennai. ECMWF takes it to north AP and it makes the UAC fizzles out.

Our view : Let us stick to what we believe and it will rain in Chennai tomorrow with UAC expected to shift back again near South AP coast. If not there is something called “Tomorrow”.

Note: This forecast may completely fail, in case the UAC moves directly up into North AP Coast as predicted by ECMWF.

1,442 thoughts on “UAC weakens and moves north, However Chennai to get Rains

  1. UAC and the nature has;the final calll – it is really depressing – the relentless assessment by the various experts has gone for a toss – Cheer up guys – rao,GTS, selvan,susa, ameen – it is difficult to post all the hardworking souls Kea is a great site – am a silent observer though..

  2. I have been silent observer for years and blog occasionally..Nature has the final shot. It’s always on safer side not to expect too much than get disappointed..Hope mother nature never betrays us. I feel rains are not far away. With onset of SWM hope we catch some intense TS from west. We have been relentlessly waiting for months to see good rainfall over chennai..Hope it happens soon..Cheers.

  3. at present 2 systems brewing over there. actually all tropical weather will come under same cycle that is “Hadley cycle” Pacific ocean related sub-circulation is “walker circulation”. which is directly related ENSO.

    active east-pacific hurricanes will do harm by 2 means.
    1. east-pacific hurricanes is indicative of Elnino-strength, so walker circulation will be more towards east-pacific.
    2. active east-pacific hurricanes means, regular elnino will become temporarily elnino-modoki (by the phenomenon of cooling Nino 1+2 SST relatively to nino 3.4 by removal of moisture over there)

    It is well documented in literature, Elnino-modoki will enhance system formation over Arabian than BOB. Reason is so simple: the descending limb of walker-circulation will be right-over west-pacific & adjoining BOB.

    application of above principle to present UAC:
    2 back to back east-pacific hurricanes means, Classical Elnino temporarily turned to non-classical Elnino-modoki. hence descending limb of walker circulation right-over BOB. Hence increase in Shear-value and sudden weakening od UAC.

    1. Consequences of pressure gradients are spontaneous when compared to consequences related to SST-gradient.
    2. Will try to explain based on MJO & SOI after receiving today’s BoM-SOI

    CIMSS-home page:

  4. Due to influence of HPA outer bands UAC weakened but soon its going to relocate and convection to be replaced for Rains in Chennai.

  5. Ooty 10c at 7 no Rains Night So cold is more…now bit cloudy… expecting more showers…

  6. The rains bands and UAC is expected to come close only by Night. So dont fuzz about rains in the morning.

  7. New Development of Cloud band is started to form and two convection placed to the east of nellore is going to converge.

  8. Rainfall in first week of June itself is a rarity. You should be happy that some areas got some light rain yesterday.

  9. Tirupati 1 – 3 Day Weather Forecast Summary: Heavy rain (total 153mm), heaviest during Tue night. Warm (max 36°C on Tue afternoon, min 27°C on Tue night). Wind will be generally light. Is this going to happen guyzz??

  10. Nothing is lost till night. Expect rains too. All i can see is dejected comments. We have to understand the fact it moved up. Its beyond our control. The 700 hpa clearly shows why it is moving back toChennai in a day or two. No more posts. Please dont flood the blog with negative comments.

  11. so this UAC finally proven to be unqualified air circulation. I have no hopes on it. atleast monsoon has set over kerala in full speed.

  12. OMG….SOI increased by 1.6 points per 24hrs. This is biggest gain in months time. Now I understood about UAC sudden jump towards north and might have bombarded the ridge and got weakened. SOI’s sudden increase may not be good for a system to strengthen. Hope it will recover slowly.

  13. Chances for a good spell of rain starts from today evening till 5th early morning. Quantam of rainfall depends on the wind direction on the given day. My guess is western suburbs will get the maximum.

  14. Good Morning,

    When i wake up today morning and saw outside and realised that there was not even drizzle last night, then i know that bloggers will come up with negative comments, as expected we could see that flown today morning. This is very much common. However we need to realise one thing that predicting UAC is very much tougher than predicting a Cyclone. UAC can shift places in a giffy. We are forecasting based on some of the forecasting models and the conditions available, but i would still insist bloggers not to get disappointed since the UAC has not died, hope it will move towards us to some extent from tonight.

    Yesterday evening i made a comment saying that we will get some passing showers last night and good rainfall expected from today afternoon or evening, still i would say at least by tonight we will get rainfall. I also request you people not to give the quantum, we have said this several times, we saw that some of us saying 100 MM, but don’t do this in future, you can say that there will be a light rain or moderate rain or heavy rain or very heavy rain. Since you are saying the quantum, it raises the expectation of bloggers and some of them might say it outside, this will surely get us the bad name. Please avoid it henceforth.

    Getting rainfall in June itself is big task, but this summer we had lesser amount of heatness in terms of averages and now good cool start to June, this itself is bigger for us but again i would not rule out rain in next 24 hours.

    Also we have SWM around the corner, there wont be a demand for moisture incursion, hence we are still having chances and till tonight we can expect some showers for sure.

    Dont forget this is an ELNINO year, i already gave the forecast in April saying May will be cooler than average temp, but June will be hotter than normal, hence lets have patience towards rain and remember this is not NEM season.

    Even ELNINO comes with Positive IOD this June, we had above normal rains in June 1997, even though we had lesser than normal rains from June to September that year. The same phenomenon is raising now, that is why i always compare 2015 ELNINO year with 1997. We have good month ahead even though it is going to be hotter June.

    Even though it is risky forecasting rains for Chennai, i would love to do it.

  15. Today morning in my house there were black ants which are grouping and was carrying food in its mouth and shifting its house, before i could take a pic it vanished, they shift with food before rainy season begins. Last year i shared a pic of the same incident.

    Hence rain is not far away from us….

  16. Long Range Forecast, which has been already posted, to recollect it… only June month looks favorable for Rains, Dry Periods are expected during July, Aug, Sep

    June Month

    July Month

    August Month

    September Month

  17. June 2 ..tis day was expected highly by ss group for electric storms. dashman, we r waiting to see the action in south Chennai.

  18. I remember posting here in the blog few day’s back saying gfs forecasting 43 degree for Chennai on june 1st.. ethu thaan gfs correct ah solluthu?

  19. i had been to Annur on the Mettupalayam- coimbatore stretch last couple of days. It was scortching heat in the mrg, but late night for 2 hrs rains lashed like hell with severe thunderstorms and disco lightening.. pleasant morning yesterday and on the way back to chennai, light rains near tindivanam and chengalpet. chennai is much cooler compared to last week.. hope UAC changes mind and path to reach chennai tonight and bang. one big shower is enough to keep city cool for a day.

  20. Wish all bloggers learn from our very own Novak Nole. Rain or shine life goes on. Does not complain about anything. Never gets disappointed when a TS misses his area.

    • Ayyo, indha postla edho ull artham irrukumo…Evaru enna solla varaaru…Puriyaleye…BTW Kea, Agumbe is starving actually. Nothing nothing meaningful so far this year…As usual, we will wait, we will wait…As Sun spot 15 always says, let the SWM rains touch coastal Karnataka, I feel we stand a better chance…

    • Not bcos of UAC.. I feel it got disturbed bcuz of tat mid level high pressure area in east central arb sea.

  21. Clear and windy here. Last 2 days thunderstorms formed towards evening but moved away. Only drizzles.
    Kodai 23 mm today.

  22. Already lot of catch up to do for Nunga.
    Normal for Jan – May period – 98.6 mm
    Rainfall received – 23.2 mm
    Deficit – 75.4 mm
    Normal for June is 76.2 mm. Will the deficit increase or decrease at the end of this month?

  23. another twist in the tale:

    The Pune based Indian Institute of Tropical Meteorology’s (IITM) extended range prediction on Monday said that monsoon may hit Kerala on June 2 or 3, which is sooner than most thought. The IITM said the rains may arrive in a day or two under the influence of a low pressure system developing over the southern tip of peninsula. The institute also attributed the weak activity till June 11 to the movement of low pressure system towards the Oman coast instead of India.

    “The activity looks weak till June 11, and by June 24, southwest monsoon is likely to cover most parts of the country, except west Madhya Pradesh, Rajasthan and parts of Gujarat region,” the scientist said.

  24. Guys i am ajuravi….logged in through my gmail hence its displaying my full name…Hope you guys remember me…I follow you guys often even though i dont post in this blog…

  25. Cyclone in Arb sea…Gfs updated ..Skirting towards west coastal areas of india..then to gujarat & to pakis..

  26. Its Kanyakumari again to get widespread rains, Tamil Nadu Rainfall ending 8.30 am on 01.06.2015
    The upper air cyclonic circulation over southwest Bay of Bengal off north Tamilnadu coast now lies over west central and adjoining southwest Bay of Bengal off south Andhra Pradesh coast between 2.1 km to 3.6 km above mean sea level. Hail storm was repored in Krishnagiri and Kodaikanal district.

    in mm (min 15 mm)

    Pechiparai – 75
    Avinasi – 71
    Pegumbahallah – 66
    Pillur – 55
    Colachel – 52
    Kaundampadi – 50
    Vedasandur – 48
    Nangavalli – 48
    Coonoor – 47
    Karamadai – 45
    Mettupalayam – 40
    Coonoor Pto – 40
    Tirupuvanam – 38
    Chittar II – 37
    Adayamadai – 36
    Sathyamangalam – 36
    Chittar I – 36
    Pochampalli – 33
    Annur – 32
    Kalasapakkam – 31
    Yercaud – 31
    Perundurai – 30
    Palaviduthi – 30
    Bhavanisagar – 30
    Barur – 28
    Salem – 26
    Mullangivilai – 26
    Kumarapalayam – 26
    Periyakulam – 26
    Ammapet – 25
    Chengam – 24
    Kulasekahram – 23
    Periyanaickenpalayam – 22
    Natrampalli – 21
    Puthen Dam – 21
    Perunchani – 21
    Bhavani – 20
    Mecheri – 20
    Nagercoil – 20
    Olapalayam – 20
    Thiruparappu – 19
    Pappireddipatti – 19
    Jolarpet – 18
    Musiri – 18
    Ketti – 17
    Palacode – 17
    K bridge – 16
    Uthagamandalam – 16
    Vaiyampatty – 16
    Balmore – 15

    Kea Weather –

    Vagaries Rainman –

    Tamil Nadu Weatherman –

  27. Season’s first named tropical storm Andres has now strengthened to a Category 4 hurricane in the eastern Pacific. On Sunday night, Andres had maximum sustained winds of 220 kmph. By the time it reaches the open waters of the East Pacific, which is relatively cooler, it will start weakening.

    The Category 4 hurricane is far away from the landmass and is expected to gradually weaken as it moves forward. Andres is expected to remain in the sea for another 48 hours and will start decaying thereafter. In the next 24 hours, it is expected to become a Category 3 hurricane. Furthermore, it will then weaken into a Category 2 hurricane. In the next 4 days, it will become insignificant.

    Meanwhile, another tropical depression Two-E has been formed nearly 400 miles off the coast of the Mexican Riviera. The tropical depression has the potential to become a tropical storm. Once it converts into a tropical storm, it will receive the name, Blanca.

    In the next 24 hours, the depression will gain strength. Furthermore, it may become a Category 3 hurricane. However, the storm will not be a threat to life or property. As it gains momentum, it will keep moving away from the coas

    – See more at:

  28. Comparing 2015 with 1997

    In 1997 May IOD was 0.49 and increased to 1.02 in June.
    In 2015 May IOD was 0.42, almost similar.

    In 1997 May ELNINO was 1.2 C.
    In 2015 May ELNINO was 1.1 C.

    In 1997 the SST was above average over Central and East Equatorial Pacific, the same thing happening now also, the West Pacific above average SST is reducing as per latest SST Anomaly map.

    In 1997 MJO emerged in Phase 1 by June 12th and stayed there till June 15th and emerged in Phase 2 by June 16th, there might be a delayed onset of SWM in Kerala that year, not sure about it. In 2015 MJO likely to emerge in Phase 1 by today and in Phase 2 by 04th.

    During 1997 June, Chennai got around 75MM, this is above average for the month, normal is 57MM, but we got below normal rainfall through out SWM season. NEM was excess.

    Since the values are same we might get above normal rainfall this month and below normal from July to September. NEM will surplus this time going by the values.

  29. Friends, Seeing the comments yesterday and today and summarize.. PJ, Rao and few others analyzed few parameters based on HPA / UAC and various charts and explained clearly why they expected rains. They were so confident about their theory and mingling with their experience, they had informed that it will rain this week.

    It so happened that the UAC moved to North than the expected path.. which comes under the probability theory. Now that it has moved away, we obviously saw clear skies with sunshine from early morning.This has been explained too in the posts below.

    Now, showing frustration and asking if the theory failed leads to no where. It is all in the learning curve. Instead, let us all try to understand these concepts and analyse by ourselves and debate over how this actually happens. By doing that, we could evolve better as a team.

    Rain or shine – let us aim to understand nature better and even after 50 years – may be with 100’s of super computers, nature will win again. That’s for sure.

    • Wow wow, Shabassh …SPZ..So some thing needs to trigger you …as always precise, consice and only the truth..Bare truth…

    • In simple Terms

      Y it is not raining based on forecast . . . . . . .

      Forecast in the man made one…. this shows us, that v are not equipped / technically good to forecast Nature

    • Very well written. Honestly and personally neither I am disappointed or otherwise, but somehow I felt last few days – this is my personal view – right from the models to forecasting – there was no confidence -even for those who projected it – This is what I felt – could be in their own back of their mind they must have felt this time nature can play a truant – most of the time I would say 90% and above – Kea Forecast have been the best – confidence level were very high and technically very sound in their approach and they have set highest standards – keeping that mind let us move on – we have hectic SWM ahead with us and not to get bogged down as how it has happened etc.

  30. Top 5 as per IMD chennai so far,
    Kodai 54 cm
    Uthagamandalam 43 cm
    Salem 38 cm
    Madurai ap 37 cm
    Pamban and tondi 32 cm

  31. evening TS cannot be ruled out and weekend rains on the cards for Chennai from Friday late evening hopefully.

  32. I am kind of feeling that , UAC will continue to move North and probably fizzle out, but this should have aided the SW monsoon pull and monsoon should set in by tomorrow or day after. IF that happens, we can expect TS by Week-end for sure.

  33. Uac not at all weakened. vorticity @ 500,700 hpa level not weakened how it weakened?. only it lost clouds and went north. it is likely to move SW towards chennai as said by pj sir. and after coming close it will organize its own super rain bands as it comes out of hpa effect.

  34. Can we analyze ?
    1. What made the UAC go north ?
    2. Why do you think the UAC will come back SW to chennai lat.

  35. Shankar,

    Why it moved up

    This is the reasoning the UAC was steered north along the ridge line of the HPA in 500 HPA as u can see in the mid level steering, the HPA over Central India hardly has any steering winds and it is very weak. U can also see the wind confluencing point where the rains are going to form depending on the moisture level –,12.31,2048

  36. Guys,

    One thing to clear all of you,

    UAC cannot trigger SWM onset, UAC is at upper level above 3.0KM from sea level, but SWM winds are monsoonal winds which will carry moisture so cannot climb to higher levels, max it would be from surface to 3.0KM level only.

    Hence there is no relationship between UAC and SWM winds trigerring, both are different.

  37. Pj sir said Nothing is lost till night. Expect rains too. All i can see is dejected comments. We have to understand the fact it moved up. Its beyond our control. The 700 hpa clearly shows why it is moving back toChennai in a day or two. No more posts. Please dont flood the blog with negative comments.


    • i have hope on the wind confluence. And the moisture to be pumped in by the UAC. Wont lose hope.

  38. Rh value over chennai is moderate to good today and hence we need only Popups to form towards nw of us to get rain in the evening

  39. I would rather tell that predicting rain for other places are easy when compared to chennai, predicting rains here is a very high task for even for experts so guys don’t blame any of our blogger or experts

    • Convergence happening at chennai latitude? Then we can surely say that atleast drizzle possible

  40. I think theres nothing there now to bring meaningful rains here in and around Chennai, The UAC missed Chennai but happy it brought rains to the interiors.

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