Sunday, May 10, 2015

Monsoon Watch - 4...2015...10th May

Forecasting Methods adopted for the Indian Monsoons:

Gowarikar(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 leans on, and believes in the "Gowarikar 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 alongwith Dynamical models for a personal analysis and estimate. 
15 initial parameters from the months March, April and May are used to analysis 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.

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 versa. 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.

1. Seasonal Low: Indicator: -ve
The heat is fluctuating with M-1 and M-2 in the Rajasthan/Sindh regions from the 3rd/4th of May, so varying chances for the seasonal low to form and establish itself, at least by the 15th.Today the pressure at MSL is 1002/1004 mb, with the core at 1000/1002 mb. Gradient not enough.
The sub Continent hot spots have just about touched the 47c mark in Pakistan (Balochistan/Sindh) and around 46c in India. Should head for the 50c mark in Pakistan 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 15th of May.
Currently the ITCZ is near the Equator.

3. Jet Streams: Indicator:-ve
A Westerly trough has totally "dis -organised" the flow, and the "wave" from M-2 has blocked the smooth flow from the East. Easterly flow will now commence from the 16th May at 8N.(As predicted, M-2 is strong and showing very intense convection over Pak Punjab, Indian Punjab and HP on Sunday).
Sub Tropical Ridge (STR): The STR is a significant belt of high pressure . It tilts equatorwards with height. During the week, it was located between 8°N & 12°N at 200 hPa.

4. Cross Equatorial Winds: Indicator: +ve
Well established in the Southern Hemisphere region. SE winds, with sufficient speed hitting the East African coasts, and gaining sufficient speed as Westerlies South off Sri Lanka.
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 25/26c, While the required SST in First week June is 17/18c. (Required to form masses of Monsoon clouds in the warm central Arabian Sea).

5. 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 El Nino now. But, there is a possibility of a full fleged El-Nino event occurring as early as July. Now, this would result in "severe" break Monsoon condition in 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.

Limited pulses from the Eastern Pacific area, that is S.China sea, would mean lesser 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, move  thru Central India and into Gujarat and even into Sindh (Pakistan). El-Nino, even a mild one, would sort of restrict these puslses, 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 mild conditions (presently on) to prevail and hang on till September. again, a 50-50 chance for such conditions.

Rainfall Estimate for Monsoon 2015 for India and Pakistan will be published here in MW- 4 Additional on 16th May...



Mukesh Chandarana said...

Rajesh Sir... Waiting for the post eagerly...

Mukesh Chandarana said...

Let's hope for the best...

SVT said...

It seems southern west coast will get heavy rains for rest of the month from 14th May onwards. Even Mumbai may get light rains in weekends.

Evewrest said...

I have a question. Forgive me if it sounds foolish. Is there any correlation between a) ENSO/IOD and b) WDs going deep into May?

Dattaraj said...

Will ongoing thunderstorms activity in south India affect monsoon arrival / rainfall quantity ?

NilaY Wankawala said...

Latest update from Australian bureau of meteorology

El Niño in the tropical Pacific

The tropical Pacific is in the early stages of El Niño. Based upon model outlooks and current observations, the Bureau's ENSO Tracker has been raised to El Niño status.

El Niño–Southern Oscillation (ENSO) indicators have shown a steady trend towards El Niño levels since the start of the year. Sea surface temperatures in the tropical Pacific Ocean have exceeded El Niño thresholds for the past month, supported by warmer-than-average waters below the surface. Trade winds have remained consistently weaker than average since the start of the year, cloudiness at the Date Line has increased and the Southern Oscillation Index (SOI) has remained negative for several months. These indicators suggest the tropical Pacific Ocean and atmosphere have started to couple and reinforce each other, indicating El Niño is likely to persist in the coming months.

International climate models surveyed by the Bureau indicate that tropical Pacific Ocean temperatures are likely to remain above El Niño thresholds through the coming southern winter and at least into spring.

El Niño is often associated with below-average winter and spring rainfall over eastern Australia, and above-average daytime temperatures over the southern half of the country. However, the current May to July outlook suggests much of Australia is likely to be wetter than average. This is because a warmer-than-average Indian Ocean is dominating this outlook. El Niño is expected to become the dominant influence on Australian climate during the second half of the year.

Rajesh said...

Evewrest: Enso conditions refer to El Nino pr La Nino..that is warming/cooling off the Peru coast. IOD is the temp difference in the Indian ocean...and bears no direct relation or connection

Dattaraj: On gong thunder activity is normal for the peninsula..please refer to the MW-1 and MW-2. It will help bring in moisture inland.

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