Monsoon Watch - 2 (18th April 2013)
Further Analysis of the parameters as discussed in MW-1.
1. Seasonal Low: As the average day/night temperatures in the Northern/Central Sub-Continent areas have shown a distinct warming up, and the -ve factor from the previous MW (last week) discussion shows some improvement (though still -ve). Heat waves are seen in the Central Regions and Eastern coast now.
But, the point to note is the "white" region stretching down from Western Rajastahn thru Western Maharashtra into Karnataka. This is attributed to the persistent below normal night temperatures. A prominent "white" is also seen in the East/Central region last week.
However, comparison with previous years shows the difference this years. In 2010, the first 45c touched on 10th. April, and on the same day Nagpur was 44c, Delhi 42.8c. Soon on 15 th April 2010, Nawabshah (Pakistan) soared to 47c, Simla to 28.2c on 16th, Ganganagar, Akola and Hissar to to 46c.
But, 2011 and 2012 were similar to this year. This year also, we are yet to reach 45c anywhere in the Sub-Continent, as was in 2011 and 2012. Into the 3rd. week of April now, and a prominent heat wave is missing.
As on 18th. April 2013, the lowest pressure, in the Thar Desert region is at 1002 mb. (though 2011 was 1006 mb, 2010/2012 was at 1002 mb this time) and this "low" region is restricted to a small area. As mentioned, it normally should reach a low nadir of 994 mb in June, and with 1008mb in the South Arabian Sea, a perfect gradient is created to attract the south -west winds towards the coast.
Rest of NW India too shows a marginally Higher reading of 1004/1006 mb
The quick formation of an optimum Seasonal Low was delayed due to persistent A-3 and A-4, and absence of heat wave in Central and Northern regions of the Sub-Continent.
Thunderstorm activity in Southern Tibet is also seen to be picking up.
2. The ENSO is neutral in the Pacific Ocean, with a further warming of the SST in the past 2 weeks. NINO 3.4 is warmer by about 0.1c, but NINO 3 is cooler by 03c over the last 15 days.
The SOI is at a high level at but remains within values indicative of neutral ENSO conditions. The latest 30-day SOI value is +5.1.
3. Last week, the Cross Equatorial winds, which originate from the Southern Indian Ocean as SE winds, and cross the equator to become South-West, were weak, and not developed due to the cyclones in the Southern Indian Ocean. With both the cyclones being a spent force now, we see the re-organisation of the Southern Hemisphere SE winds, as no hindrance is seen to occur now.
Let me explain, that the winds on crossing the equator break into 2 branches. 1) gushing into the Arabian Sea, and 2) moving into the Bay of Bengal.
In the Western Sector, the Arabian Sea branch is still struggling to get organised. Here, sufficient wind speed off the Kenyan coast has yet to form the SE flow required. But should re-organise fast. SE winds are now getting organised and weakly striking the East African coast between the Equator and 5N, though still weak.
The Northwards movement of the ITCZ will surely hasten and strengthen the winds.
Today, we find, in the Eastern Sector, the winds south of the equator better organised for the Bay branch, in the region south of the Andaman Sea. SW Currents are seen off the Sumatra coast. Thunder cloud (Cb) developments are seen near the region South of the Equator.
And that is exactly where the start should be for the SWM to arrive at the Andamans. Upper winds at 100-400 hpa are vigorously aiding the lower winds to attain the required strength.
Currently, the weakening "Imelda" depression has created a "damaging" trough and pushed it Southwards, literally breaking the Mascarene high pressure zones in the South Indian Ocean. Main High reading now 1029 mb, and 2 more Highs (in the forming) have been observed, one at 1018 mb and another at 1025 mb. between Madagascar and Australia. The "Power House" of the Monsoon winds is slightly behind schedule, for this time of the season.
4. But the pre Monsoon Low in the Bay is still elusive. As discussed, we should normally see a low sometime after the 15th. of April. The high pressure region in the Bay, at sea level, no longer prevails. Never the less, the encouraging factor is the likely formation of an UAC in the Andaman Sea.
Seeing favourable winds, and a slightly positive MJO still in the region, we see this as favoring a low formation. But, it has to be quick, as the positve MJO moves away Eastwards by the 25th. It is forecasted that a negative weak MJO phase may settle in the Bay region last week of April.
Another factor, which helps the winds gain strength, and bring more moisture into the Indian landmass, is the sea temperatures on both sides of the Peninsula. Optimum (warm) temperatures will hasten and create more clouds, and help in faster forming of the lows from the Bay.
This parameter, "normal" and tilting towards "favourable" as on date.
I have put up the SST of last year on date. Comparison with this year shows it is favourable in the South Indian Ocean, where cooler waters will create a High pressure quicker.
5. To bring the existing SE winds above the equator, the ITCZ should move northwards. Around 1st. of May, this should cross the equator. The ITCZ should now come back to its Northward position, as the effectives "Lows" created by the Rossby Wave have fizzled out. The Western end is still dipping to around 5S, but the Eastern end has moved Northwards and is almost at 10S.
So, overall, we can summerise as:
Parameter:1) Normal, 2) Normal. 3) -ve, 4) Normal, 5) Normal.
Most parameters are "Normal" as of today.
In today's situation, Monsoon arrival in Kerala could be on normal dates in Kerala and the Bay Islands, and the NE states.
We will put up the estimated date of arrival in the MW-3.
But, situations can change fast, and by the time we discuss the next MW, some factors can suddenly become +ve or -ve. So, MW discusses and follows the developments as they emerge, and discuss the parameters as is where is.
No model can commit from today when the Monsoon can arrive. Quantum of rain forecasting in the month of April, for a period right through September is an impossible task.
Next MW up on 26th. April with firm Dates of Monsoon Arrival.
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.