Monday, May 06, 2013


Monsoon Watch - 4 2013 Quantum Analysis, Part -1.....6th May

Note on Forecasting Methods adopted for the Indian Monsoons:

Gowariker(1989) developed parametric and multiple power regression (MPR) models with 15 predictors for LRF of AISMR, which were later modified in 1991 to include 16 predictor parameters. The parametric model is qualitative and indicates the likelihood of the monsoon rainfall to be excess or deficient.
Thapliyal (1990) evaluated the relative performance of multiple regression, and Navone and Ceccatto (1994) have used 'feed-forward' neural network technique for the prediction of Indian monsoon rainfall with two predictors (500 hPa ridge location and Darwin SLP tendency from January to April). 
The results of a recent work by Krishna Kumar (1997) indicate that a single component accounts for about half of the total variance in the predictors.

Most of the studies on LRF of Indian monsoon rainfall were based on empirical or statistical techniques till 2010. IITM, Pune has recently implemented the state-of-the-art coupled climate model, the Coupled Forecasting System (CFS) developed by the National Centers for Environmental Prediction (NCEP), USA. These statistical techniques range from simple correlation analysis to advanced procedures.

Vagaries' Views:

I still have faith, and believe in the "Gowariker Method" with 16 parameters. The results of this old but proven method has been successful. For Vagaries' forecast and analysis made in the "Arrival and quantum Monsoon Watch" series, I combine a few of them along with Dynamical models for a personal analysis and estimate. 

15 initial parameters from the months March, April and May are used to analyse and forecast the simulation of Indian monsoon rainfall during June to October. These initial conditions were carefully selected to span the evolution of both the atmosphere and ocean.
Calculating the amount of rainfall, region wise, is of utmost importance, as SWM contributes to almost 80% of the annual total rainfall over India.

The performance of Vagaries' Monsoon Watch Quantum analysis is evaluated for the amount of summer monsoon rainfall over Indian monsoon region during June to SWM withdrawal in 2 phases.

The 500 hpa parameter is of importance in April. The mean latitudinal location of the 500 hPa ridge along 75°E in April over India, first identified by Banerjee (1978), is considered to be one of the most important predictors. 
The mid-tropospheric anticyclone over southern India migrates from 11.5°N in January to its northernmost position of 28.5°N during July. From October, the ridge starts shifting back southward. A more Northward location indicates better performance of the monsoon and vice verse  It also showed that the negative correlation of the March ridge was more dominant with the monsoon rainfall of the peninsular India, while the positive correlation of the April ridge was more dominant with the monsoon rainfall of Northern India.

ENSO factor in arriving at the rainfall amount is also of importance. The interface is the sea surface: that is where the transfers of water (evaporation/precipitation) 
and momentum occur. An accurate coupling of the fast atmosphere to the slow ocean is essential to simulate the ENSO, which in turn can simulate the inter annual 
variability of Indian monsoon. 
Unfortunately, getting an accurate, or near to accurate forecast of the ENSO for the next 2 months is difficult, with no guarantee of accuracy or performance surety.

We see neutral conditions now. But, there is a possibility of a mild El-Nino event occuring as early as July/August. Now, this would result in "severe" break Monsoon condition in late July or August. That is the last thing we want. But I would not endorse the event as yet. I would give it a 50-50 chance.

Pulses from the Eastern Pacific area, that is S.China sea, would mean depressions and systems originating from the Bay. 'In Situ" systems and systems from the Far east would contribute to the rainfall to the east Coast thru Central India and into Gujarat and even into Sindh (Pakistan). El-Nino, even a mild one, would sort of restrict these pulses  and in fact encourage WDs into coming down south, more South than normal. 
But, for this, we would have to hope and pray for the Neutral conditions (presently on) to prevail and hang on till September. Again, a 50-50 chance for Neutral conditions.

Regarding the IOD parameter, recent forecasts from a few  coupled models  suggest  the possibility of development of a weak negative Indian Ocean Dipole event after July 2013.

1. Seasonal Low: Indicator: -ve
The heat is picking up in the Rajasthan/Sindh regions from the start of May, so good chance for the seasonal low to form and establish itself, at least by the 10t/12th.
Today the pressure at MSL is 1002 mb, with the core at 1000 mb. The sub Continent hot spots have just about touched the 46c mark (it is already Late. Refer MW-1) and should head for the 50c mark by around 16th May.

2. ITCZ: Indicator: Normal
As it is by the 10th, that we should have the ITCZ nearing the Equator. Only then would the Bay branch of the SWM could commence in the Southern Bay by the 12th of May.
Currently at 5S almost all along the 2 sectors..though a bit more Northwards in the Eastern Sector.

3. Jet Streams: Indicator:-ve
These are streaming away in a Westerly direction above the 20N line. They are just about getting Easterly around 5N. Needs a rapid change now. 

4. Cross Equatorial Winds: Indicator +ve 
Well established in the Bay region. W/SW winds, with sufficient speed hitting the S.Myanmar coasts, covering the Bay Islands with >30 knts, and could herald the arrival of the SWM on time there.
Arabian Sea winds are now picking up, and rubbing the Somali coast at sufficient speed in getting the "Somali Current" established. The SST off the Somali Coast is 26c, While the required SST there in First week June is 18c. (Required to form masses of Monsoon clouds in the warm central Arabian Sea...refer previous MWs).

5. Bay Scenario: Indicator +ve
The normally anticipated development is happening.
The formation of a system, BB-1, is on stream.(i maintain BB-1 for this 2nd UAC, as the first UAC which formed on the 5th, and moved away Westwards, did not descend to sea level, and still remains {as on date} as an UAC). A stronger phase MJO would help in the quick formation and strengthening of the system now under formation.

This, BB-1, will drag the ICTZ Northwards, and in all probability  pull the SWM into the Andaman Islands as the system deepens. 
Hence, SWM could well enter Southern Andaman Sea by the 12th/13th, it seems.

Second Part of MW-4 with Map of Monsoon Rain Estimated quantum Forecast region wise will be put up on 11th May.

These are my personal views, and should be depended upon commercially or otherwise.

9 comments:

Anantha Krishnan said...

Your initial assessment seems ominous for the performance of monsoon . are we staring at another patchy monsoon performance ? a negative IOD and weak El Nino might severly derail the monsoon in the crucial months. Will look forward to your may 11 assessment

naveen123 said...

the initial reports depicts that it to be a weaker monsoon this time to
...lets wait for 3 or 4 days to observe the movement of the depression.this will give us a clear cut idea about monsoon

sset said...

Rajesh sir- just wanted to check - most of the terms you have mentioned -"regression","neural networks"- they all come under statistical data mining - Predictive Analytics. Infact "neural networks" is now being replaced by other techniques like Byseian and other decision trees models - for faster computation and convergence of results.

sam khan said...

Thanks to all the rains in the northern regions of india that has occured in the month of april, for delaying the heat, and also delaying the low pressure built up.

sam khan said...

if these western disturbances continue in this manner , we may loose south west monsoon in the coming year's.

Ron said...

thank you sir..very informative read...

emkay said...

Rajeshbhai, good to see you are first of the blocks in alerting the possible severe break monsoon, purely on an observation basis, if june brings in relatively wide spread heavy rains we are in trouble for july the critical month

sam khan said...

The winds in the Arabian sea are picking up quickly, and are hastening towards the kerala coast, along with good moisture build up.

rajesh said...

Check Mangalore Live Cam..on the Links...great !