Tuesday, June 16, 2015

Posted Wednesday Afternoon:

An UAC has formed in the Bay off the Odisha coast at 700 mb level...Expected to persist at that level, while descending to Sea level as a Low ( BB-1) by Wednesday Night.

The upper level trough at 700 level extends Westwards from the UAC to the Arabian Sea ...We can expect another UAC at the Western end of the upper trough W/SW or maybe S of Gujarat in the Arabian Sea.
This will be the Northern tip of the already strengthening Off Shore Trough ( West Coast). The strengthening is seen as the isobars are dropping, the 1000 mb bar now over Mumbai, and 1004 mb bar over North Kerala.

 Posted Tuesday Night:

A UAC is expected to form along/off the Odisha coast by the 17th. This UAC will strengthen at 700 mb level, and deepen at that altitude. The system can descend, but deepen with height on constant location by the 19th.
BB-1 is expected to form in the Bay off the Odhisha coast by the 18th of June..Initially as a Low at 1000 mb. Expected to deepen in the waters to 998 mb off the Odhisha cost by 20th June. 
BB-1 will cross the Odisha coast around 20th at 998/996 mb ,and track NW.
The Monsoon axis is expected to Move to its normal position by this time. 

As the axis moves North, S.W.Monsoon will cover Odisha, Chattisgarh and W.Bengal starting from 18th June..gradually moving . 
Expecting into Kolkata after 19th June..
Monsoon will start moving into Eastern U.P. after 20th June.

Mumbai will get the occasional showers next 3 days, with the average rainfall around 10-15 mms per day. No persistent constant rainfall till Friday...
Mumbai santa Cruz received 23 mms till 8.30 pm IST (12 hrs) Tuesday. Vagaries (South Mumbai) measured 10.7 mms in the same period.

Gujarat Special:

Saurashtra and South Gujarat region, at some specific Places, have got super and abnormal "pre monsoon" rains this year..


Gondal....last 24 hrs 105 mms...Total In June 428 mms...That is 68% of the total Seasonal Rains !!
Kotdasangani...Total  In June 183 mms...29% of the seasonal Total  !!

South Gujarat

Valsad District: Totals In June: Kaprada  301 mms...Seasonal total for Kaprada is 2885 mms., Valsad 221 mms, Umergam 216 mms,  Pardi 199 mms.

Bharuch District: Jambuser got 45 mms rains in last 24 hrs ended Tuesday Morning. 

Bharuch has received 94 mms till Tuesday Morning (Total). 
Jhagadia is the wettest till today in Bharuch District with a total rainfall of 143 mms. 

Surat District: Highest is Umerpada with a total rainfall 186 mms, Chorasiya 185 mms, Palsana 166 mms and Mangrol 127 mms.

Dhari in Amreli District has got 174 mms total.

Report on BB-1 and Monsoon advancing into Odisha and Bengal on blog later tonight..11 pm IST


Abhijit Modak said...

Rajesh Sir : What may be the reason of such abnormal heavy pre monsoon rain activity for Suarashtra ??
As this year, Bay branch is still weak so East India onl waiting from long for there SWM arrival in Bhubaneshwar-Kolkata belt . So No Bay low to help Gujarat rain. Even Arabian sea don't have any UAC or MTC's off Gujarat/Saurashtra coast !! So how can only off shore trough till Gulf of Khambat can pour such heavy there ?? Also we see weak SWM onset as 700 hpa not properly organised and winds were weak !! So what condition helped for so much rain and that too without of "SWM onset" there ??

Rajesh said...

Abhijit: good question showing enthusiasm...was waiting for such a question...now, you will find your own answer ...do you see a trough at 700 mb level, remnant from Ashoba ?This has embedded as a low in the weak off trough Northern part at 700 level...and got concentrated rains .. Coastal South Gujarat and parts of Saurashtra...only 2 districts..restricted to the well fed regions affected by UAC...Now you tell me, how long these rains will last there ?

Kaneyen said...

Dear Abhijit,
Pre monsoon rains are EXCESS [or ABNORMAL]not only in Saurashtra but to large extend it is excess at many parts of the country. There has been some correlation with this excess pre monsoon rain and SWM for the entire country. that is SWM will be deficient in many parts of the country. The following reasons may be attributed for this:

(a) The relatively weaker in strength of Mascarene High and its ensembles.

(b) The tilly-tallying nature i.e west-east drift from its expected NORMAL position.

(c) The "sea - change" that occurred in Pacific and Indian Ocean and its impact over atmosphere over there. That is the ocean-atmosphere reaction plays vital role.

(d) When the SWM strength in lower level troposphere is weak formation of UAC helps to bring rainfall but it is amount will be less. This is an alternative mechanism and moisture absorption at local sea [with lesser area] will be converted into rain.

(e) This can be evident {or widely generalised} of frequent appearance of optical phenomenon like "CARONA" in the sky. Where as during good SWM period more "HALO" will be seen generally.

Unknown said...

Sir, I was too asked the same that there are any reason behind this rain or it's just 'aasmani sultani'? Now I think 700hpa became well organised and set to it's normal with proper onset of monsoon then rain in SE saurashtra will decrease and now SW saurashtra starts to get their typical monsoon rain. ...

Abhijit Modak said...

@ Kaneyan: Thanks for adding more points for clarification. But I would say Rest of India and saurashtra pre monsoon rain are of different timings

Rest of India had good rains from March to May as there were systems present like WD dipping south till Rajasthan. Then good LWD for S. Interior Peninsula also Low/UAC off Kerala coast in May end so overall due to weather systems present we can know the excess rain fall had occurred.

But Saurashtra rain were sudden without any storng system also non of models predicted such heavy even though it was isolated to 2-3 district. So was more curious on it. Also timing of Saurashtra rain was when monsoon was on door with just few 100kms as NLM was present till 20-21 N latitude that is of near Gujarat only. So comparing Rest of India Apr-May rain with this Saurashtra mid June is not comparable I think

sset said...

For past 5 years Gujarat has shown trends of displaying last moment surprises... (a) 2013 september extreme rains 300-500mm in 24hrs for 3-4 days guess 2013 September phenomenon is reverse of 2015 june present condition
(b) 2014 june Nanuk Arabian sea cyclone.. many parts of Gir forest region indeed received more than 300mm of rain in 24hrs
Regarding essence of 700hpa -- took from wiki..
Maps using isotherms show temperature gradients, which can help locate weather fronts. Isotach maps, analyzing lines of equal wind speed, on a constant pressure surface of 300 mb or 250 mb show where the jet stream is located. Use of constant pressure charts at the 700 and 500 hPa level can indicate tropical cyclone motion. Is this reason for popularity 700hpa rather than 500hpa - 700hpa is closer to earth surface than 500hpa.

sset said...

For information
1hpa = 1mb (however hpa is widely accepted SI unit)

sset said...

Guess when low forms over the bay, excess rains over GUJ Saurashtra may decrease...but September 2013 may haunt again???

Unknown said...

Rains in saurashtra is always subject to research. ...in last ten years there was several occasions in which many centres shown extraordinary results. ...it's not new new for saurashtra if some centre receive 50% or more than it of its annual average within 24 hours. ....some years ago khambhaliya and jamnagar Received 2500+mms during monsoon which is almost 5 times of their annual average ..

Atul said...

When can we expect rains in ghat section? It's depressing :(


Rajesh said...

Atul: Ghats rains increasing this weekend...from Friday...see updated blog

Rajesh said...

Kaneyan: Thanks for the Update and information

Rajesh said...

Gaurav Raninga...you have mentioned of erratic rains in 2013 in Gujarat...and wondered why >See 29th Sept post for rain amounts and 30th Sept post for an explanation in our meeting then..see here

Nagpur Downpour.... Cloudburst on 23rd between 2.30 am -3.30 am...98.5 mms a t city AWS Railway station 24 hr Rainfall till 8.30am of 23-9-2...