Tuesday, May 10, 2011

Readings of 10th May:

Hottest in Asia: Larkana (Pakistan) 48c, Nawabshah and Jacobabad 47c.

Hottest in India: 45.2c at Khajuraho, Agra 44.7c, 44.5c at Brahmapuri.

Lows above 30c in India: Khajuraho 31c, Gwalior 30.7c, Gondia 30.4c, Kota 30.3c, Satna 30.2c. No lows above 30c noticed in Pakistan.

Next 4 days (Wed thru Saturday). We may see fairly heavy precipitation in the NE states, sikkim and Eastern Nepal. Thundershowers in Kerala and south Karnataka.
Some change expected in peninsula from Sunday.

Strong Westerly dust raising surface winds in Rajasthan and Gujarat are likely to prevail next 3 days, and Lower Sindh region of Pakistan. This would raise the day temperatures a bit more (refer to region in Vagaries' map of yesterday).

Sindh region of Pakistan could see the year's first 50c before the end of this week.
Strong dry westerlies at around 40 kmph in Karachi will keep the day temperature within 36c. Nights however will be around 27c.
After some rain on Wednesday, Islamabad will start warming up from Thursday onwards, and can reach 37c by Saturday.

Monsoon Watch - 6.

Seasonal Low:Indicator: -ve

An interesting release has been put by by IMD on the one to one co-relation between a "coolish" April 2011 and estmate of SWM arrival and quantum. It says, in years when W.Ds have dominated, it is not necassary that it has an effect on the SWM in any way. No one-to one relationship could be observed between surface heating of northwest India during the pre-monsoon period and the monsoon rainfall, it concluded.

But, I feel, one parameter is sure to have a direct bearing. The formation of the seasonal low. It surely is dependent on the quantu of heat in the Northern plains of the sub-continent.
Frequent W.Ds during April this year, and 2 in May, have kept the day temperatures in near normal levels, and the minimum temperatures much below normal (as much as 7c) in interior Mah and Karnataka, has resulted in a delay in the formation of this low.

Today, as on 10th May, we see an area of 998 mb in Central Pakistan region. But, due to W.D. effect, the 998 mb has been elongated into the sub Himalayan areas, in U.P. This was referred to in the Vagaries on Sunday.
What we now, see is a core area developing in the Thar desert region of Pakistan, at around 998 mb. This is what we were waiting for and refering to in the previous MWs.

Sub Continent: The jig-saw puzzle of the monsoon can fit in properly in the bay and Arabian sea, but I only hope the below par heating and seasonal low formation in the north do not play spoilsport. The heating even today(Tuesday) is mediocre, with the highest in Pakistan today( 10th) at 48c, Larkana, and with only a stray 45c at Khajuraho and Agra in India.

The heat low just about touched 998 mb in a small area on the 10th. A difference of at least 16mb in the pressure is required between the MSL at Trivandrum and the pressure in the heat low to create a gradiant to pull the monsoon winds and clouds inland.

Cross Equatorial Winds: Indicator: Getting Neutral.

Strong SW winds have gained strength in the Bay. Perfect re-curving at the equator has developed, and the SW current is prominent in the Bay. But, I have postponed the SWM arriaval from the earlier estimate of 12th May (South Islands) to 16th May. NW winds are pushing away any chances of any low forming in the next 5 days.

SST in the Bay, and the Typhoon Aere may host a low in the Bay around the 16th. This could pull up the SWM in the region for the time being. I say temporarily now, as the current MJO wave might weaken considerably after 15th May, and hence do not see much future for the system in the Bay.
On the Western front too, the said MJO wave seems to be weakening after the 15th.of May. As per normal time frame, it would remain weak, in this (Arabian Sea) sector till the 4th of June.

Water SST: Indicator-ve
If we compare the SST anomaly map with that of the same time last year( shown below), we see the Arabian Sea is much cooler this year, if the same normal temperature is taken into consideration. Last year the warming trend at this time was more, and this year the same region is cooler.

However, the Somali winds as seen in the streamline map, are picking up, and a distinct cooling off the Somali coast is still to occur. I feel, the SST of the Arabian Sea vis-a-vis the Somali current and other conditions are yet to gear up for monsoon clouds to start forming in the central region, around Maldives and off the Sri Lanka coast.

The ITCZ now runs along the Equator from the African coast to Sumatra Island. Normal, for it to touch the equator around the 10th. (For more read previous MW).

Conclusion: With the aid of a low, (pulse from the Pacific), SWM could advance into the South and Central Bay Islands around the 16th of May. Further advance will depend on the strength of the low.

Arabian Sea branch will see the SWM advance into the Maldives region by the 22nd of May.However, a brief halt there might result in the SWM advancing into Kerala around 4th June.


Anonymous said...

Do you expect any major tropical activity in ARB??..from PWP..thankz

Rajesh said...

@PWP.As per my estimate,I see no major activity in the ARB Sea, till May end at least.
We see the SWM advancing in the Maldives region by around 20th. And till end of May, the only activity seen is the SWM advancing into west coast of India.

svt said...

In last 3-4 years we had cyclone in bay between 15th may to 25 may and cyclone in arabian sea in 1st week of june. Any chance of cyclone this year or below normal heating in northen plain will have effect on this one.

Rajesh said...

See a system forming in the Bay around the 17th May.Will be restricted to a deep low.
Nothing for the arabian Sea in May.

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