As expected by Bloggers, UAC forms and the wait for it to descend starts

For the last few days, bloggers were keenly watching the formation of UAC in various models. As expected, the UAC (Upper Air Circulation) over SW BOB / Comrin Sea has formed and it is well defined in 850, 700 and 500 hpa levels. This UAC is going to bring lot of rains to Southern Tamil Nadu in the initial stages. Whether it is going to descend to lower levels and ultimately to sea level as a LPA (Low Pressure Area) and subsequently intensify into a Cyclone has to be seen in coming days. There is no consensus in the models.

700 hpa

Meanwhile, the CEW (Cross Equatorial Winds) is picking up in velocity and feeding the required moisture. With unstability in higher levels and moisture in lower levels, it is an ideal system in the making. Track this unique system formation in Kea Blog with various insights.


As for as Chennai is concerned, No more Kathri Veyil (Hot days) and no chance of Temperature hitting 40 C in the next week. As moisture is increasing, it will be more sultry and due to Cloud cover, the nights will be hotter as radiation heat is trapped. Coming to Rains in Chennai, there is 100% chance of Rains from this UAC in Chennai as the UAC is seen moving NE towards North TN coast. The date and quantum will be put up as separate post as and when things are clear in a day or two.

1,365 thoughts on “As expected by Bloggers, UAC forms and the wait for it to descend starts

  1. this is another Chance to see whether ECMWF which predicts rains from Tuesday or GFS which predicts rains only from Saturday are the best when it comes to rains in Chennai.

    GFS always disregards 500 hpa circulation. ECMWF respects it.

  2. Ameen, I already told to pray for SOI not to go below -10. It should start increasing from today onwards to avoid any N/NE track.

    • it will increase or decrease.. whats your take and are the condition favorable for rising od SOI?

  3. MJO already started emerging into phase 6. No single cyclone till today (in history of cyclones) crossed indian coast with MJO phases 5&6 with SOI below -10.

  4. One major difference is GFS charts already indicate a slight LLCC east of SL but ECMWF charts don’t. That could cause all the difference in the runs.

  5. Perfect topic and conditions are good and moisture bearing clouds from SE this could be a early indicators for Rains to Come.
    Monsoon like Clouds around Chennai.

  6. The dip in jet-stream pattern now started elevating with respect to latitude. The other day this dip was below 10N. Now this dip was elevated above 10N and stayed around 12N. This is good sign for SWM-dynamics or related any tropical disturbances’ formation.

      • It (UAC/system) will stay around STN-SL ( or enter Arabian ocean without intensifying) or try to escape towards Orissa or above.

        If it falls below -10 then we (NTN/SAP) have to forget this UAC.

  7. One or Two places might have isolated Showers over North Coastal Tamilnadu and asusual South Tamilnadu will get Moderate to Heavy Spell.

      • Thanks PJ. Yes. Not sure when met is going to get this right 🙂

        By the way, why Forca has reduced the towers? (sorry if i’ve missed the earlier discussion.

      • I am always sceptical about Foreca. Yesterday night i posted that it will reduce towers.

  8. High level cloud in Bangalore.. No rain since 4-5 days .. Humid and hot weather prevailing.. When the situation will improve?

  9. Foreca drastically reduces tower but shows cloudy conditions till may 20th! Clearly shows it follows ECMWF.

  10. Everyone went with Foreca and ECMWF. But the King GFS is showing massive rains from 17th. This is the true rains.

  11. LPA / WML right over Chennai on 17th. This is the rains which will happen in Chennai. Not the Foreca or ECMWF

    • PJ.isn’t this yesterday’s run?
      They are changing their forecast every single run.

  12. pj sir,
    most of them telling it will not move NW and it will move into NE.means will it move into arabian sea?

    • Deepak, what did i say. It will rain. I will tell u personally when it will. When i am confident. Next few days, we may not get widespread rains, if rain at all.

  13. The UAC descends down and LPA forms and From 16th May, massive rains to Start in Chennai. It is going to be pretty heavy rains for North TN.

    No more cyclone by GFS. Its all North Tamil Nadu. Rao, Congrats, u predicted it spot on.

  14. very positive post to start for this hot week..hope things materialize.. Bay already started in action..

  15. I don’t know about other districts but Sri lanka in for some MASSIVE rains :O
    Lucky them.

  16. Monsoon type of climate around chennai.
    Thick dark clouds hovering around.
    Nice respite from heat 🙂

  17. Seems like a low intensity cyclone is possible for Chennai. Happy that kea has promised 100% chance of rain. Good Bye Kathiri!

  18. Dep/DD close to N.TN and S.AP coast.
    Should start getting heavy rans with windy conditions from may 16th.

  19. pondy getting rains…very cloudy in chennai…expecting rains to tonight/tomorrow morning…lpa will form tomorrow

  20. So finally GFS has done something good.
    They have removed the land cyclone they predicted yesterday 🙂

  21. UAC gives rain to Kanyakumari, Tamil Nadu Rainfall ending 8.30 am on 10.05.2015
    The trough/wind discontinuity from Telangana to south Tamil Nadu now extends from east Madhya Pradesh to south Tamil Nadu across Vidarbha Telangana and Rayalaseema at 0.9 km a.s.l.

    in mm (min 10 mm)

    Pechiparai, Kanyakumari – 55
    Valparai Taluk Office, Coimbatore – 35
    Kayattar, Toothukudi – 10
    Mettupatti, Madurai – 30
    Chittar I, Kanyakumari – 27
    Vazhapadi, Salem – 26
    Veerapandi, Theni – 24
    Bodinaickanur, Theni – 24
    Dindigul, Dindigul – 20
    Trangambadi, Nagapattinam – 20
    Kothagiri, Nilgiris – 18
    Kannimar, Kanyakumari – 18
    Manjalar, Theni – 15
    Karaikal, Karaikal – 15
    Tiruppur, Tiruppur – 15
    Palladam, Tiruppur – 15
    Madurai AP, Madurai – 13
    Sholayar Dam, Coimbatore – 12
    Tiruppur, Tiruppur – 12
    Kalugumalai, Toothukudi 12
    Vadipatti, Madurai – 10
    Sathiyar, Madurai – 10
    Periyanaickenpalayam, Coimbatore – 10
    Sulur, Coimbatore – 10
    Pudur, Toothukudi – 10
    Nagapattinam, Nagapattinam – 10
    Kuzhithurai, Kanyakumari – 10

    Kea Weather –

    Vagaries Rainman –

    Tamil Nadu Weatherman –

    Flodded Dindgul Road and Undulated clouds in Aruppukottai (Undulated clouds happen to high shear and clouds are punctured)

    • lol. If it rains and if she was jailed. they will say Nature is crying. If she is released, they will say rains are blessing her release.

      • ha ha yes, exactly sir….i am happy as i can now return to home after finishing my evening shift..if she had been proved convicted, these people would have made me to stay till wenesday

      • Yeah it is beyter these people getreleased else t hey will all stall the govt day 2 day activities dharnas etc etc…

  22. Pattukottai (Thanjavur Dist), Tuticorin (Toothukudi Dist),
    Adirampatnam (Thanjavur Dist), Kollimalai arg (Namakkal Dist),
    Thoothukudi port AWS (Toothukudi Dist)- 4cm

    Vadipatti (Madurai Dist), Kalugumalai (Toothukudi Dist),
    Vilathikulam (Toothukudi Dist), Tiruppur (Tiruppur Dist),
    Kamatchipuram (Dindigul Dist), Hogenekal (Dharmapuri Dist),
    Manamelkudi (Pudukkottai Dist), Peravurani (Thanjavur Dist),
    Sholavandan (Madurai Dist- 3cm

    Arantangi (Pudukkottai Dist), Mudukulatur (Ramanathapuram Dist), Gudalur (Theni Dist), Usilampatti (Madurai Dist), Surangudi (Toothukudi Dist), Maniyachi (Toothukudi Dist), Kadaladi (Ramanathapuram Dist), Aranmanaipudur (Theni Dist), Bodinaickanur (Theni Dist)- 2cm

    • I’m expecting by seeing gfs uncle charts it shows a depression in GOM on 13 th may.. so I’m expecting rains to start from tomorrow evening /night!!

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