Tuesday, April 10, 2018

Monsoon Watch - 1... 2018....10th April 

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 35 days away from its normal date of arrival from the shores of India ! Yes ! its just 35 days from the First touch of shores...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 its share of 2018 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 CURRENT 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  During SWM Onset in Early June.  

B)below indicates the actual situation of the parameters situation today (9th 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 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 1008/1010 mb. This enables a good gradient 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 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 as on 9th April:
1. Cross Equatorial Winds:
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 in the required region. A small High at 1031 mb.  Four "weak" Lows are tracking in the region. We have to wait for these "lows" to dissipate.

But things are unorganised  below the Equator.( Wind Chart Below)
Cross Equatorial Winds should start forming, and taking shape from mid -April, especially in the South Indian ocean region. 
Initial forming of SE winds off the East African Coast has not started from below the equator. Weak  Easterly  flow below Sri Lanka (in the Southern Hemisphere) can be see, though a bit dis-organised.

ITCZ:This Seasonal trough passes from the South  Arabian Sea to Andaman sea after the withdrawal of SWM in Oct. Shifts further south in Dec. Moves North during SWM
Now near the equator.

Today, the winds  North of the Equator are Northerly (around a "high") in the Arabian Sea, ... and are Easterly in the  South of the Arabian Sea. 
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 not  forming as of today, Southerly flows are required to strike Sumatra.

Indicator: -ve

2. Seasonal Low: Now, this year, the heating in the sub continent has started from March , with  Heat Waves in Maharashtra, Gujarat, Central India and parts of NW India.. The above normal heating in many parts continues in April. 
On an average, March has registered normal temperature (average day and night),  

and, with below normal rainfall...-48%. These are a points in the formation, or a quicker formation of one of the important pre monsoon weather requirement, the seasonal low.

In June,the seasonal low, which stretches to Arabia from 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/Sindh region. There is a isobar of 1010/1008 mb covering almost the entire Indian region. In the "core seed" area, it is 1006 mb. (The ultimate low in the core, in June when ready, should be 994mb.). This progress is bit tardy. 

The current Line of Wind Discontinuity (weak in S.Madhya Mah Region) 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. 
Indicator: -ve

3. ENSO is on way to a Neutral Stage. 
This year also, like last year, we also base our observations on the Multivariate ENSO Index (MEI).  An attempt is made to monitor ENSO by basing the Multivariate ENSO Index (MEI) on the six main observed variables over the tropical Pacific. 

These six variables are: sea-level pressure (P), zonal (U) and meridional (V) components of the surface wind, sea surface temperature (S), surface air temperature (A), and total cloudiness fraction of the sky (C). (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 MEI is computed separately for each of twelve sliding bi-monthly seasons (Dec/Jan, Jan/Feb,..., Nov/Dec). 

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 (Feb/Mar) MEI has changed to -.502 (in Jan/Feb was -0.731), for a slightly decreased ranking, now moving towards neutral stage. 

SOI is falling, and is now at  + 12.4.
Sustained positive values of the SOI above +7 typically indicate La Niña while sustained negative values below −7 typically indicate El Niño. Values between +7 and −7 generally indicate neutral conditions.

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.  ONI latest is -0.9... Just marginal, could get lower in the coming months...But at this stage, it cannot be surely mentioned, that an neutral stage could fully develop by June, the onset time of our South West Monsoon.
( 0.5 - -0.5 is neutral. Above 0.5 is El Nino, and below -0.5 is La Nina).
La Niña conditions are present.
* Equatorial sea surface temperatures (SSTs) are below average across the central and eastern Pacific Ocean. A transition from La Niña to ENSO-neutral is most likely during the March-May season, with neutral conditions likely to continue into the second half of the year.
Indicator: Heading towards Neutral.

4. Another pre monsoon seasonal normal requirement is the creation of an initial 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, (With BB-1 having already been formed prematurely) 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 in the Bay. The required SW winds may not yet form at least for the next 4/5 days.
Indicator: -ve

Summary for arrival Date: Parameter 1). -ve   Parameter 2). -ve,  Parameter 3). Neutral Parameter  4). -ve.
Summary: Tilted towards slightly Negative, as of 10th April. Parameters analysed as of now show slow progress for Monsoon Advance on time.

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 22nd. 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.. http://rajesh26.blogspot.in/2012/03/importance-of-monsoon-forecast-for.html....March 19th 2012


Rajesh Kumar said...

Well Explained.

NilaY Wankawala said...

Every season SWM series begans with your master stroke , current 2018 being no exception. Rajesh sir being doing this since years and he is very consistent in this matter. He is the only one to reply upon as he releases his forecast with detailed and in depth study of each parameter and he is very well in time always before IMD commences its commitment on this count every year. Your indepth analysis is a treasure not only for weathermen but also for a common man as you explain each parameter so lucidly. Pleasure to read your work as always been. Lets hope parameters changes positively as you lift the curtain in the follow up to the first one.

Konkani Don said...

I think monsoon will be delayed. By June no La Nina,monsoon below normal.

Sunny said...

Skymet weather is so excited about the monsoon season .
That they keep posting monsoon stories every day.
Latest story is ...about Goa n Mumbai monsoon n summer heat comparision 😃

Vinod Desai said...

Awesome !!

Vijayanand said...

Superb data

Strong Western Disturbance is seen affecting the country and the subcontinent. Heavy rain and snow reported from Himalayas, and rain/thunder...