Saturday, April 16, 2011

Monsoon Watch - 2.

Further Analysis of the parameters as discussed in MW-1.

1. Seasonal Low: For this parameter, the -ve factor from the previous MW discussion is maintained, as the average day/night temperatures in the Northern Sub-Continent areas remain in near normal/below normal range.

IMD map of day temperature of the 15th April anomaly explains this.

A comparison with last year shows the difference this year. In 2010, the first 45c was 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.

This year we are yet to reach 45c anywhere in the Sub-Continent.

The quick formation of the Seasonal Low due to absence of heat wave in Central and Northern regions of the Sub-Continent, continues to be un-favourable. Into the 3rd. week of April now, and the heat is missing.

As on 16th. April, the lowest pressure, in the Thar Desert region is at 1006 mb. (Last year 1002 mb this time) and this "low" area 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 gradiant is created to attract the south -west winds.

2. The La Niña event continues to decline in the Pacific Ocean, with a further warming of the SST in the past 2 weeks. On an average, it is warmer by about 0.2c over the last 15 days. The warming is consistent with the life cycle of past Niña events.

SOI was last measured at +26, equivalent as yet to a strongish LA-Nina event.

3. Last week, the Cross Equatorial Monsoon winds, which originate from the Southern Indian Ocean as SE winds, and cross the equator to become south -west,were weak, and not developed .

Let me explain, that the winds before crossing the equator break into 2 branches. 1) gushing into the Arabian Sea, and 2) moving into the Bay of Bengal.

Today, we find, the winds south of the equator better organised in the Bay branch, in the region south of the Andaman Sea. SW Currents are seen off the Sunmatra coast. And that is exactly where the start should be.(See extreme right of chart).

The Arabian Sea branch is still struggling to get organised. Here, a fall in wind speed off the Kenyan coast has disrupted the SE flow.Not a healthy sign,but could always re-organise fast.

The Mascrene high pressure zones in the South Indian Ocean, at 1030 mb, between Madagascar and Australia, have been observed, and the "Power House" of the Monsoon winds is slightly behind schedule,for this time of the season.

4. 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, is not very "normal" and tilting towards "un-favourable" as on date.

Put up the SST of last year on date. Comparison shows it was much warmer last year, i.e. above normal.

But the pre Monsoon Low in the Bay is still elusive. As discussed, we should see a low sometime after the 15th. of April. But as on today, a high pressure region prevails over the Bay.

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, is in its "normal" position, as of now, at 5S. An indication is the Australian Monsoon Trough, now stationary north of Australia, around 10S, with TC embedded.

Ceasing of TC activity is a must for the ITCZ to start shifting.

So, overall, we can summarise as:

Parameter:1): -ve. 2): Normal. 3) -ve. 4) -ve. 5) Normal.

Most parameters are running -ve. as of today. In today's situation, Monsoon arrival in Kerala could be delayed by about 4/5 days , and on normal dates in the Bay Islands, and the NE states.

But, situations can change fast, and by the time we discuss the next MW, some -ve factors can suddenly become +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. Things get clearer by first week of May. Vagaries' (in MW) normally remains true to estimates around early May.

Next MW up on 23rd. April.

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