These reports are my personal views, study and observations. Estimates and forecasts are also my own calculations and views, and may/may not tally with any other estimates. This may not be used for commercial purposes. The author is not responsible for any commercial loss from this article, or this series of articles.
The Monsoon developments, as they unfold, will be analysed and discussed and explained in Vagaries.
The South West Monsoon is just about 32 days away from its normal date of arrival from the shores of India ! Yes ! its just 32 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 2015 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, of this series will be chasing and closely following up the actual developments of the monsoon parameters, and analysing 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
B)below indicates the actual situation of the parameters situation today (12th April).
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 powerfull 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 gradient to pull the SWM Northwards and inland.
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 parameters, later a few more develop.
1. Cross Equatorial Winds from Southern Hemisphere.
2. Seasonal Low over India/Pakistan.
3. ENSO Status.
4. Pre Monsoon Low in the Bay.
Position today 12th April:
1. Cross Equtorial Winds should 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 yet to form "full fledged". Just a small High at 1029, and 2 "lows" in the core region, adding to the delay.
A tropical storm " Joalane" is also hovering around, delaying the proper arrangements for a series of Highs. (Map Below)
But things are un-organised below the Equator.( Wind Chart Below)
Initial forming off the East African Coast, has started from below the equator. and the weak SE flow towards Eastern Africa can be see, though a bit dis-organised.
As the Monsoon strikes the Andaman Sea by mid May, developing wind currents ( Westerly) are required to be observed initially near the Eastern side of the Southern Indian Ocean, and this is weakly forming as of today,
Tropical Storm forming in the S.Indian Ocean, means a marginal delay in the Mascrene highs strengthening.
ITCZ today is near Equator to -3N.
The winds above equator revolve round a High in the Arabian Sea, and are Westerly South of the Arabian Sea.
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 yet to be seen forming as of today.
2. Seasonal Low: Now, this year, the heating in the sub continent has yet to start , with no substantial Heat Waves worth writing about.. The above normal heating in the NW is yet to start, as March was relatively normal to below normal, I would say.
The anomaly rainfall map for March justifies the reason.
This is not much of a plus point in the formation, or a quicker formation of one of the important pre monsoon weather requirement, 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 North Rajasthan region. There is a isobar of 1010/1012 mb covering almost the entire Indian region.In the "core seed" area, it 1008/1010 mb. (The ultimate low in the core, in June when ready, should be 994mb.).
The current Line of Wind Discontinuity should stabilise around Central India perpendicular down into the Southern Peninsula. 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.
3. ENSO is on threshold of El Nino. This year, for the first time in our MW series, we also base our observations on the Multivariate ENSO Index (MEI). (Negative values of the MEI represent the cold ENSO phase, a.k.a.La Niña, while positive MEI values represent the warm ENSO phase (El Niño).The updated (February-March) MEI has risen by 0.18 standard deviations to +0.65, for a slightly increased ranking, now solidly above the weak El Niño threshold (upper 30%ile).
Similar behaviour was observed during the 2004-05 El Niño in particular
SOI is falling, and is now at -11. Constant value below -8 is indicative of El Nino.
The Oceanic Nino Index (ONI) is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. The last 5 consecutive 3 monthly overlapping seasons show the fast establishment of an El Nino event. Just marginal, could get stronger in the coming months...But at this stage, it cannot be surely mentioned, that an El Nino could fully develop by June, the onset time of our South West Monsoon.
Equatorial Rossby waves are interfering and influencing the MJO waves,and is clearly showing signs of weakening in this diagram.
Indicator: Heading towards El Nino.
4. Another pre monsoon seasonal normal requirement is the creation of a low in the Bay by the second week of April. This is necessary 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 East winds. The required SW winds may not yet form at least for the next 3/4 days, as a High is likely to form later this week off Odisha Coast.
Summary for arrival Date: Parameter 1). -ve. Parameter 2). -ve, Parameter 3). Normal. Parameter 4). -ve.
Tilted towards the negative, as of 12th April.
New Readers, please note, These initial Parameters are normally (every year) considered in MW Series to gauge and estimate the arrival date of SWM, not strength. Time of arrival normally indicated in MW-3, and strength after 27th April. There are more parameters are to be considered, as and when they are developed and to be taken into consideration.
MW-2 on 21st. April.
While IMD still defers its forecast, IMD should have taken up this job in right earnest much earlier. Vagaries had mentioned this earlier here.. ....Reference reading may be done here also.