Thursday, April 11, 2013

3:30pm, Lonely T.shower seen over S.tip Tamilnadu and over Jharkand, S-W,central Bengal ... 

At 3:30pm, Hyderabad = 42 C, Varanasi = 40 C, Thiruchirapalli = 39 C, Ahmedabad, Patna = 38 C, Kolkata = 36 C, Delhi = 35 C, Amristar = 32 C

#IPL - Bangalore - Temperature at 4:30pm = 35 C (feels like 33 C), Humidity around 20% and with mild breeze from East.

South West Monsoon - 2013 - Watch #1

The Monsoon developments, as they unfold, will be analysed and discussed and explained in Vagaries. 

Do you know, the South West Monsoon is just about 35 days away from its normal date of arrival from the shores of India ? Yes ! its just 35 days from the Southern most point of India on the South Andaman Islands, Indira Point, where the normal arrival date is 15th May.
And its about time we start the follow up of its progress and monitor its developments. 

The Sub-Continent is eagerly awaiting for its share of 2013 monsoon rains !

This annual series is a follow up and chasing of the South-West Monsoon. Every article in this series explains the synoptic situation as it actually is, and based on the day's position, the date and quantum of rains as on THIS SITUATION.

It is very important to firstly estimate the date of arrival of the S W Monsoon, as year to year, variations in dates of onset of the monsoon can occur and there have been several occasions in the past when the monsoon arrived over certain parts of the country about a fortnight earlier or later than the normal dates. 
The SWM has the  weatherman tearing at his hair for the exact date or time, extent and progress. This is never 100 per cent sure though various weather models are used to calculate this event.

Initially, in the first  few articles, this series will be chasing and closely following up the actual developments of the monsoon parameters, and analyzing its progress regionally for calculating and estimating the arrival date. 
We are not yet contemplating the quantum of rains or the monsoon strength as yet. 

There are 2 parts to this article:
A)-This is the Ideal Conditions (Map) During SWM Onset in Early June. and 

Vagaries map

B) below indicates the actual situation of the parameters situation today (10th April).

A) Very very briefly, let  us first understand, that the "power house" of our SWM is actually based far away in the southern Hemisphere. The main "generating factory" is the Mascarene Highs, between SE of the Madagascar coast and Australia. The SWM is born down South, 4000 kms from the Indian Mainland !

The proper formation of these high regions,(1032/1034 mb at least) will boost and create proper SE winds to lash the East African Coast near the Equator, and then turn perpendicular towards SW in the Northern Hemisphere. 
And the formation of the "Tibetan High" is another factor. An anti-cyclone in the upper atmosphere over the Tibetan Plateau. During the formation stages, there will be thunderstorm activity in the SE parts of Tibet during the months of April and May.

To generate a powerful  SW wind, the cross equatorial flow must be strong and gusty. SW winds (ultimately upto 600 mb levels) then are capable of riding on the warmer Arabian Sea waters (Arabian Sea Branch of SWM) and bring cloud masses towards the West Coast of India. In the Bay, similar SW winds are generated (Bay branch of SWM), but from SE winds below the equator, just below Sri Lanka.

And to attract the SW winds, again, we need a good proper "seasonal low" to develop in the Sub-Continent. This seasonal low, normally should start forming around Barmer, Rajasthan, by mid April, and at its peak stretch upto Arabia. Seasonal low at its peak, in June, should normally be around 994 mb, and the ridge around Kerala should be 1008 mb. This enables a good gradiant to pull the SWM Northwards and inland.

B)-In this initial stage, we will observe the basic root and foundation, the initial 4 parameters only, and the initial seed of the monsoon. From these parameteres, later a few more develop.

1. Cross Equtorial Winds from Southern Hemisphere.
2. Seasonal Low over India/Pakistan.
3. ENSO Status.
4. Pre Monsoon Low in the Bay.

Position today:
1. Cross Equatorial Winds should normally  start forming, and taking shape from mid -April, especially in the South Indian ocean region. 
The Mascarene Highs are the main "Power House" of the South -West Monsoons. This generates the South -East winds, which after gaining strength, cross the equator and become south west. For a proper High to form in the South Indian Ocean, the cyclone season (Low pressures) should completely die down from that region.

As on date today, the Mascarene Highs is forming, though in initial stage, and 1 segment, of 1034 mb is seen. (Map Below)

But things are messy below the Equator.
Currently the MJO has stalled in the Eastern Indian Ocean region, with 3 embeddded lows.

For the Bay branch, we have an interaction of a Rossby Wave and the MJO, which has formed a cyclone heading towards the NW Australian coast. 

Aust Bur of Met

This Cyclone "Victoria" is expected to move Southwards, and further pull down the trough towards the South. Tropical cyclone forming in the S.Indian Ocean off the Australian Coast, means a marginal delay in the Mascrene highs strengthening. ..ITCZ today is around 7S.

Initial forming off the East African Coast, has been disturbed by another Cyclone "Imelda"off the NE coast of Madagascar. The winds are pulled towards the cyclone, and re curve back from the coast in an anti clock wise direction around the circulation. 
Part of the SE winds today converge back Eastwards towards the system (in the trough) NE of the Madagascar Island, South of the equator. 
The winds are Northerly above equator right down till 5S.

Yo Surfer wind Charts

As the Monsoon strikes the Andaman Sea by mid May, developing wind currents are required to be observed initially near the Eastern side of the Southern Indian Ocean, and this is weakly forming as of today, but disturbed by TC "Victoria"
Indicator: -ve

2. Seasonal Low: Now, this year, the heating in the sub continent has just about started in the Eastern regions. The above normal heating in the NW is yet to start, as March was relatively normal I would say. The anomaly map for March shows a warm North, average Central regions and cooler South. This is not much of a plus point in the formation, or a quicker formation of one of the important pre monsoon weather requirment, the seasonal low. In fact, the minimum night temperatures are still below normal in central and NW India. 

The current one week into April is also pretty much the same.

The seasonal low, stretch over Arabia thru India, normally starts forming in the Barmer and adjoining regions in the second week of April. 

Today, the MSL is around 1008 mb in the Sindh/Rajasthan region. There is a isobar of 1008 mb covering almost the entire Indian region.In the "core seed" area, it 1006 mb. (The ultimate low in the core, in June when ready, should be 994mb.). 

This progress is fairly ok. The Line of Wind Discontinuity should stabilise around Central India perpendicular down into the Southern Peninsula by mid April. This enhances the speed of the Seasonal Low formation. Normally is required to start taking shape for the monsoon by the second week of April. 

Indicator: -ve

3. ENSO is now Neutral. Last SOI reading observed was +9.0.  

The Oceanic Nino Index (ONI) is based on SST departures from average in the NiƱo 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. The readings for the last 2 weeks is constant, no change. Thus Neutral conditions prevail. Neutral conditions expected till June at least, so this parameter will not disturb the advance and will not interfere with the date.
Indicator : Neutral

4. Another pre monsoon seasonal normal requirment is the creation of a low in the Bayby the second week of April. This is necassary to trigger off the flow and formation of lows from the bay.
Progress this year is bad, as the Bay shows no signs today. No forecast of any low as of now. (in 2009,a low formed by the 12th. of April, and later it intensified into cyclone "Bijli", 2010 had no low till 3rd week of april).
Today, we have a "high" sitting in the Bay. The required SW winds may not yet form at least for the next 3/4 days, as the active trough still around 10S is interacting with the MJO.

Indicator:  -ve

Summary for arrival Date: Parameter 1). -ve.  Parameter 2). -ve,  Parameter 3). Normal.   Parameter 4). -ve.
Tilted towards the negative, as of 10th April.

Taken from
Next good W.D system is expected to reach N,N-W India on 16-Apr ... 

Before that on 13/14-Apr, a weak W.D circulation is expected to affect N.India ... 

During next 3 days, Rain expected over Kashmir and Himachal ... 
Today, low level circulation seen over S.Tamilnadu and Kerala, another one along central Tamilnadu coast ... 

Today, the circulation along E.Madhyapradesh persists and weak circulation over S.Maharastra, N.Karnataka persists .. 

Showers expected over S,central Kerala during next 24hrs and more rain ahead from Sunday ... 

13/14-Apr, a low level circulation and trough expected along N,N-E Maharastra and trough extending upto S.Tamilnadu 

Scattered rain expected for N,N-W,N-E Andhra, N.Karnataka into S,S-E Maharastra & S.Chatisgarh on Saturday.. 

Saturday, Rain also expected over E.Maharastra, S,E.Madhyapradesh, N.Chatisgarh, Jharkand, W,N-W Odisha & S-W Bengal 

#Chennai - On 14/15-Apr, the low level wind direction is expected to shift from S,S-E to W,S-W .. Temperature expected to rise up to 38 C.
#Chennai - at 1:10pm, Temperature was 34 C and having mild breeze from S-E. 

#chennai - During the past 4 days, the low level wind is from S,S-E, as long as the wind is from S-E the temp. will not cross 36 C.
11:50am, Patna airport has reported T.showers !!

12pm, W.D has cleared out from N,N-W India. Cloudy and rain seen over Bihar and N,central Bengal ...

At 12pm, Hyderabad and Nagpur has crossed 40 C.