Thursday, September 18, 2014

Follow up Posted Friday Night:
Low remains off the Odisha coast..almost same strength at 1000 mb..expected to merge with the UAC in the same region...

The jet streams are now almost fully Westerly up to almost 25N...currently 100 hPa , has its core is along Lat. 13°N with wind speed higher than 60 knots. During the week, the highest wind speed of 75 kts was recorded over Thiruvananthpuram at 150 & 146 hPa on 16th September.

Today, we also see a trough in the Westerlies in the North Pakistan region. That is why I mentioned yesterday a speedy withdrawal in NW India expected soon.
The Low in the Bay remains off the Odisha coast.

I would not like to comment now, but unofficially can say the Myanmar anti cyclone at 500 hpa ( Necessary for NEM advance winds).can be expected around the 10th of October...it needs certain parameters to form over the Bay to get started.


A 1 hour rainfall recorded 31 mms from 9 pm IST at Vagaries on Friday Night..
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Posted Thursday Night ( 18th September):

South West Monsoon is in the withdrawal process, and has withdrawn from West Rajasthan. A ridge formation, an anticyclone in the 200 hpa level, and surface winds from the NW bringing a sharp reduction in humidity ensures speedy withdrawal from Rajasthan, Kutch, Punjab, HP and Kashmir by  Saturday 20th September. 

Delhi NCR would see gusty NW winds from Saturday through Sunday. Warming up the day and sliding the night temperatures to around 23/24c.

Weekend will see hot days with day temperatures peaking at 43/44c in the Sindh region of Pakistan.
Days get hotter in Rajasthan and Kutch.

Friday/Saturday and Sunday
Contrary to this, rainfall may increase in West Bengal, with heavy falls. Odisha and AP continue to get the regular thunder showers. Increasing rains in Central and South interior Peninsula.

Mumbai City get  a cloudy morning. clouds forming in the day. Shower expected by evening in parts of city.
Rains low till 23rd,after which we may see some increase.
Similarly with Pune, low rainfall this weekend, increasing to heavy thunder showers after 23rd.

Kolkata may get thunder showers in the afternoon/evening this weekend.
Hyderabad , may benefit from a low coming after the 22nd. Thunder showers on 22nd and 23rd.
Possible of a heavy thunder shower in Bangalore on Friday/Saturday.


Glance into Vagaries' Long Term Forecast (probable):

A Low forms off the AP coast around 23rd/24th September. Seeing the scenario today, it seems due to the anticyclone in the North (by then), this system may cross into AP/TN coast, and cross into Karnataka. 
Thunder showers increase in the States of Maharashtra and Karnataka from 24th.
A slight chance, that this system may re emerge in the Arabian Sea around the 27th. Thunder showers continue in Maharashtra in that case.

A "strong" WD can be expected (seeing the trough possible in the North) around 26th/27th. If things work out well, the trough, and WD rains, can dip South till Central Sindh.

What do we wait ansd see ? What do we study in this case ? We have to monitor if a) the WD "pushes off" the Arabian Sea Low, or b) the system "pushes of" the WD.
In case of b), the system can move towards Gujarat.
These are Long Term probables, and I do not have definite answers to the outcome 

16 comments:

Vinod Desai said...

I feel south india will get rains andhra and karnataka..swm will withdraw from gujarat by next week end.

RK Chaudhary said...

Rajesh Sir, which scenario of long term forecast, a or b, could be beneficial for rain in Delhi?
SW moisture from Gujarat low or the WD??

emkay said...

Wonderful post Rajeshbhai

ANOOP RAWAT said...

Sir you mention speedy widthrawal of SWM so will be nothing like last year when it recurved into haryana . This time it may withdraw around normal date in Delhi which is 21 sept.

sset said...

All are very thankful for Rajesh sir scientific explanation. But so many "if" and "probabilities" sounds scary for NEM onset. Last year 26-sept-2013 reversal of SWM happened - monsoon axis went up - low pressure on GUJ/RAJ brought around 1000mm of rain in 4-5days!!. Explanation is in vagaries knowledge repository. If this happens again then almost entire SE India/Sri Lanka will become desert (already in that state now).

Krishnakumar Bulusu said...

HI,

As rajesh mentioned, this is exactly what we want for NE monsoon to pick up and be on time.. A low should form around AP/TN coast (15 N Latitude) to pull the NE winds...now a low forming around 23/24 lets see..

else any system which forms around orissa durign the fag end of the SW monsoon can only the NE monsoon to a great extent.

Krishnakumar Bulusu said...

Hi,

A low as mentioned by rajesh by sep 23,24 will be instrumental in shaping NE because it is likely to affect TN/AP.

I remember in 2005 NE monsoon set in as early as oct 8-9 and we had a tremendous season..

Waiting for NE..

Regards
Krishna

abizer Kachwala said...

rajesh sir, great forecast. but sir can you say about the weather on 26th and 27th sep in raigad disrict. kindly sir.please

sset said...

Guess driest spot in India as far as SWM is concerned is "PAMBAN" - southern most tip of TN - 0mm since june. Next to follow are Thothukudi,Rameshwaram,Coimbatore... < 50mm of rain since june.

sset said...


If we refer to vagaries withdrawal parameters taken from Rajesh sir 2013 august blog..
point 2 may not allow NEM to set??

Anyway I need to google to understand blogs complex weather terms...

-1. Let us initially keep a watch on the 200 hp jet streams. During the monsoon , they are Easterlies approximately below the 30N line.This is the Southern periphery of an anticyclone at 200 hp, with the core between 30N and 35N at 150 hp. Peak winds at core exceed 100 knots. Westerlies are to the North of the Himalayas.

Now, when the withdrawal process starts, we may see a deviation, gradually from the Northern regions. The anticyclone in the Northern most regions vanishes, and westerlies start taking over below the 35N.

-2. A trough, in the westerlies, in the Afghanistan/ North Kashmir region, would mean the movements of WDs in the upper atmospheres. The frequent movements of these troughs and WDs would hasten a withdrawal.

But what we need for the NEM to advance is a prominent anti-cyclone at 500 hpa over the Central Myanmar region.

rajesh said...

Sharp showers at Vagaries ( Mahalaxmi) from 9 pm IST..recorded 29 mms ...still raining...Posted Friday 9.45 pm IST

rajesh said...

RK Chaudhary: I suppose the WD option would be better, but, a WD now may not precipitate up to Delhi...

The other option will surely bring rains in Gujarat, but not extending further Nortwards

rajesh said...

sset: Good follow up ! yes, I am observing the 200 jets now, and also the anticyclone at the 850 level.
200 jet streams are the season changers....read more in the latest posting for a follow up...

sset said...

Raining very heavy and non-stop in Navi Mumbai - inline with vagaries forecast yesterday... hope dreadful rains are not back again...
But Bangalore no rain - over last few years rains are continuously eluding BANG - massive climate change - still at 250-300mm since june.

abizer Kachwala said...

rajesah sir, there were moderate rains in nagothane, near roha [raigad ] for more than 2 hours non stop light and some heavy.. what is your forecast ahead.sir weather from 22nd to 28th in this area. thanks in advance sir.kindly inform me about that.

rajesh said...

abizer: I see some thunder shower activity increasing from 24th for 4/5 days. Will see showers in the afternoon or evening during the period.