Thursday, May 29, 2008

Monsoon Watch-19
The "real" monsoon cloud mass, though not very strong and intent, has now formed today, as seen in the satellite image of 00UTC Thursday. The mass of cloud is near the mid Arabian Sea, away from the cold waters formed by the Somali current, and now gradually nearing the Kerala coast in a south-westerly direction.My personal observations are that the monsoon has hit the Lanka coast today,29th., with moderately strong winds and rain.
I see the monsoon hitting Kerala in 2 days, and then sliding north upto Karnataka coast in the next 2 days.The situation, in the northern region of the subcontinent, discussed in MW18, is gradually improving.The weak ridge in the Arabain Sea is still seen "faintly'', and the easterly jet streams at 200hpa are still yet to move north, being restricted by the westerly jets which are strong at 22N. Concurrently, the further movement of the monsoon can be restricted by a few days.
Monsoon should approach Mumbai by the 9th. Its strenght along the west coast may remain feeble upto the middle of June.The monsoon should advance into South Gujarat around 15th., and progress towards Saurashtra region in the next 3/4 days.
In fact, with the seasonal low formation being delayed this year, June rains may be deficient in Gujarat, north-west region and Maharahtra.(maybe upto mid July,as discussed in MW17).

Now, the ECMWF has, as of 0000 UTC Wednesday, given up on a major Arabian Sea cyclone. But, the 1200 UTC GFS forecast model has now shown an Arabian Sea cyclone that would end up landfalling upon Oman at the middle of next week.
I do not know whether there will be an Arabian Sea tropical cyclone next week. The situation, I feel, seem to be favorable for a monsoon low or tropical depression westward from southern India (heading towards Kerala as the monsoon current). Hence, we can observe the numerical forecast model scenarios and make our judgements on the uncertainties of the the weather !

Wednesday, May 28, 2008

Monsoon Watch-18
The weather in the northern regions of the sub continent continues to play spoilsport. The series of W.D's since the last 15 days, has effectively cooled down the region(as discussed in MW17), and to some extent, the" low" temperatures continue till today. The temperature deviation map of 26th. is not "healthy" for the advance of the monsoon. A large portion of the north is still below normal, with some regions in the Punjab region far too low for comfort. The latest IMD sea level pressure chart too is devoid of a proper monsoon low (of around 994mb), but shows a small region of 1000mb. Even on the 27th. the highest temperature in Pakistan was 47c at Nawabshah and 44c at Jaisalmer and Nagpur in India.
As per the IMD, the monsoon should advance into Kerala by the 30th., (see MW8, 25th. April).

My estimate is monsoon should advance by that date, and progress into Karnataka in a day or two, but as a weak current. Sufficient pressure gradient may take upto a week to develop and pull the monsoon further north. Hence, situation continues to project the further advance of the monsoon beyond Karnataka into Maharashtra after the 6th./7th. June.
Is there a faint indication of a ridge forming in the Arabian Sea ? Shall have to wait for a day and see, but I hope it does not.

Saturday, May 24, 2008

Monsoon Watch-17
After the discussion in MW16, a W.D. in the northern region has played spoilsport again. On the 23rd. night, rains were reported from north Rajasthan and Pakistan and some areas of Punjab and Haryana. An upper trough is hanging on in the northern region for an unusually longer period.
Now, I estimate, that this has blocked the progress of the seasonal low and the said low is presently very weakly formed, at 1000mb, in the region of northern Sindh/adjoining Rajasthan.Temperatures in the north are still to reach the normal levels as on the 24th.
Consequently, the monsoon advance can be restricted. As per the estimate in MW16, the monsoon can advance upto coastal Karnataka by 1st. June, as a feeble current. Thereafter, I foresee a halt in the progress further northwards for another 8/10 days atleast, till the proper conditions are recreated.
For Gujarat, the monsoon may actually arrive only after 15th. June. It may require another 10 days( after the vanishing of W.D.s) of sufficient heating to form a proper gradient for the advance.
Also seeing the current situation, the fast vanishing La-nina, and the "slipping" SOI index, it may be difficult, in certain areas, for the monsoon rains to be normal this year. There may be some delay and below normal rains in June/early July. Hence the initial period of June/July will have to be watched and followed closely for regions in western and central India.

Friday, May 23, 2008

Monsoon Watch-16

To continue from the MW-15, it's been a total turntable. Just the opposite of what was required has happened. No W.D. was expected, but on the 19th., a sudden trough in the upper air at 200mb. forced its way through north India, with induced lows in the lower atmosphere over the plains of north India. Resultantly, its "cold" and raining in the plains of north India now since the last 3 days. Instead of the expected heat wave when temperatures anomollies are required to be +6c, its -15c in Delhi and -5-10c at many other places in the region. Delhi with a high of 24c at Palam and 25c at S'jung, on the 21st, is 15c below normal . Amritsar, Chandigarh and Patiala were 17-18c as the minimum and all over Punjab the days were a pleasant 25-28c. Much below the normal 40+ expected during this time ! Is it May or November?
The IMD max. temperature deviation map shows the entire region in the below normal colours.
The W.D. has precipitated fairly good amounts of rain all over the plains of Punjab,Haryana and west U.P., Delhi being specially targeted with 60mm of rain at the ridge on 21st.
In Pakistan too, the heat was a bit easy today(22nd.), with the highest being 46c at Nawabshah.

The 200mb winds were still strong in the west-east direction as on the 22nd, and are expected to ease by the 25th. thus letting go the prevailing W.D.

The result of this: 1. The heat low, which was at 998 mb, is now back to 1000mb, and restricted to the Pakistan side of the border. The Indian side shows no specific seasonal low tendencies now.
2.As per IMD, a low is expected in the south-east Arabian sea around the 23rd. The existing upper air trough in the north,the "cool" temperatures there, and the absence of a reasonable heat low over the land mass of India, may direct the low to concentrate and move north-west towards south Oman.
As per ECMWF,it can become a very deep depression, or a cyclone, and cross the south Oman coast.As to when it will cross, is too early to forecast now, but could be around 1st. June. Requires monitoring after the formation of the low. The sst of the Arabian Sea(picture) shows sufficient heating for this.

As a result, if this happens, the monsoon may touch the Kerala coast by the 28/29 of May, but as a feeble current. And the feeble monsoon may slide upto coastal Kerala and Karnataka in 2 days, but remain weak for the next 6/7 days.

The Bay sst in the picture above is still seen as below normal. No forecast model indicates any major revival of rains in the bay, for the next 10-12 days.

Monday, May 19, 2008

Monsoon Watch-15
Sub-continent Region: The entire northern region has now started heating up, to almost heat wave conditions.(That is temperatures of 6c above normal).

The graph shows the temperatures of Delhi and Nagpur during the last 30 days. The "red" portion is above normal only by about 3c. Subsequently, the temperatures dropped after the first week of May. The average temperature for both cities during the period under mention is only 0.4c higher than normal.
Technically, it would be the first "heat wave" of the season, presuming the temperatures now rise in the coming days. Today, 18th. Sibbi, Pakistan recorded the first 50c of this year. Anyway, it should not be a problem for a rise in temperatures now, with no major W.D. in the offing. This will spell well for the heat low over the Pakistan/India region, now at 998mb.
Bay Region: As mentioned in the MW 14, the bay sst still remains below normal. Hence no international forecast model is predicting a further progress of the monsoon rains northwards from the current limit in the next 5/6 days.

Arabian Sea: The sst there too is still maintaining itself at the normal level. Alongwith, the cross equatorial flow in the Arabian Sea is keeping pace as required for this time, and is now established fairly well. COLA and FNMOC predict a burst of rains coming towards the Kerala coast from the 20th. -24th. Subsequently the forecast indicates a fair amount of rain over Kerala/Coastal Karnatak from th 24th.

Thursday, May 15, 2008

Monsoon Watch-14

Bay Region: Today, I was most surprised to get a message from Vinson( Business Line) to check on the JTWC site. They had mentioned the likely formation of a cyclone in the bay. I always felt that this is not a probability now. As discussed in my earlier blogs, that this low will eventually "rain off" in the north bay area within a few days. For it to remain weak, there are several reasons:-1. low convection around it. 2.back to back W.D.s,causing dry north-westerlies to push it away. 3. very much near/on the coast. 4. Bay sst not warm enough for the system to turn into anything beyond a depression at the most.
Check the bay sst anomaly above, they are still at least 1.5-2c below normal in most of the bay.

The streamline map above shows the winds weakening a bit in the central bay. The formation of a tropical storm in the south china sea in the next few days will pull the main south westerly flow of the south andaman sea towards it. Hence, I still feel, that the monsoon will advance in the bay , by the 20th. The further advance into the north-eastern states will commence only after the formation of a trough from Assam to the central bay region, say by the 25th.

Arabian Sea: Read todays forecast given by the IMD. The monsoon , according to them will advance into Kerala between the 25th.May and 2nd. June ! Leaves nothing to imagination !
If we compare the sst anomaly map above and the sst anomaly map 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(yellow) off the somali coast is now seen. I feel, the sst of the Arabian Sea vis-a-vis the somali current and otherwise will be geared up for monsoon clouds to start forming in the sea off the Kerala coast from the 25th. Another 4/5 days thence, and the monsoon can touch Kerala.

Sub Continent: The jig-saw puzzle of the monsoon can fit in properly in the bay and Arabian sea, but I only hope the sub continent heating and seasonal low formation in the north do not play spoilsport. The heating even today(wednessday) is mediocre, with the highest in Pakistan today( 14th) at 47c, Nawabshah,and with only a stray 44c at Nagpur and Vijaywada in India. The heat low just about touched 998mb in a small area on the 14th. A difference of atleast 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.

Sunday, May 11, 2008

Monsoon Watch-13

Bay Region: Carrying on from the Monsoon Watch-12, the waters of the bay have since started heating up as is seen here. The formation of a low now seems probable by the 14th. But it seems the low may not be very strong as it is likeley to form in the east central bay, around the islands of north Andamans, around the 15N region.The ECMWF also forecasts the formation of a low in the north Andaman region by the 16th., and the system may get a bit stronger before crashing into the north Mynamar/Bangaldesh coast by the 19th. As a result, the south west monsoon, already declared in the south Andamans by the IMD, will be pulled upto the north Bay by that date. Cross equatorial winds are not strong enough yet today to pull the monsoon beyond the declared limit for another 2/3 days.
Most of the strenght of the bay current is going to get pulled away by the likely formation of a tropical storm on the south china sea during the 15th.-19th. period.

Sub continent Mainland : The day temperatures are still below normal for a larger part of the sub continent. The areas under the "below normal" regions are covering most of the regions required to be under heat waves as on date. But the east coast has heated up, and Gannavaram and Vijaywada there were 45.8c (+6) on the 11th. Across in Pakistan, Nawabshah was 47c on the 11th. as the highest in the region. The seasonal low in the northern areas is still premature, and the low formation is distorted at 1000mb.

Arabian Sea: The high pressure at MSL is now prominent in the sea. In a way, this can linger on for another week without really causing any damage or diversion to the monsoon winds. In fact, this'' high'' should get the somali current winds moving fast, and strenghten them. I see the somali winds just about forming as on the 11th. Should be in full strenght by the 19th.

The jet streams, at 200hpa. over the Indian sub continent have just started their northward shift in the last couple of days. In the monsoon season. the jet streams, sometimes at 100 knots, should ideally be east-west, with the centre core at around 15N. Today they are west-east above 22N, while on the southern tip of the peninsula, the 200hpa streamline (map) shows a weak east-west formation starting.

Ideally, the monsoon should now cover the bay area by the 20th.Monsoon winds in the North-eastern states, and the arabian Sea segmant will gain strenght and progress after the 25th.of May.

Thursday, May 08, 2008

Monsoon Watch-12

Bay Region: The recent sst anolomy shows a larger area of below normal temperatures in the sea than the last posting. In fact, the cooler area has spread northwards. The unexpected cooling will not allow a low to develop in the south bay at sea level pressures, for the next 5 days, at least, from today (7th. May). Resultantly, the initial rush of south westerly monsoon winds and monsoon rains will resume in the south Andamans around the 13th., but will be restricted to the 8N limit in the bay, and may not advance northwards of 8N immiedietly after the 13th. but may take a few days. However, the IMD forecasts an upper air circulation in the south Andaman region by the 11th.

Sub continent mainland: Again, unexpectedly, yesterday's W.D. has cooled down the entire region north of 20N in both India and Pakistan for more than 2days , and brought a major portion of the in the "below normal" colours of the map. The highest in Pakistan on the 7th. was "only" 43c at Turbat , and most "hot spots"in northern and central India were below 40c, with the highest at 42c (Ramagundam,A.P.). The result is that the seasonal heat low has become distorted, more so with an induced low sitting stagnant over the Sindh/Rajasthan border area and pushing in cooler air in the region. Also with another (sudden) W.D. forming and rushing into the same region tomorrow, 8th. May (some light rain has already commenced in Jacobabad by 7th. night), no major rise in the temperatures in northern regions, could be expected for another 2 days. In fact now from the 8th., the days may remain a little below normal, and no heat wave could be expected for the next 5 days. Re-organising of the seasonal low over Rajasthan can take place only after the 12th.

Southern Hemisphere: The push from the southern hemisphere for the cross equatorial winds is now perfect. The southern MJO has weakened in the exreme east region, and hence with good south -easterly flows in the south Indian Ocean, the ICTZ has advanced northwards and could be said to be at 2S today. However, a cooler Arabian Sea and a ridge over it, prevents a straight flow of south-westerlies over the Arabian Sea. But this is normal for this time of the month, and the pressure should stabilise in the second half of May.

Sunday, May 04, 2008

Monsoon Watch-11

Bay Region: The water temperatures in the bay remains low after the cyclone. The image shows the temperatures around the centre of the bay as below normal (cyclone region), and the south bay also is seen as below normal. This has to heat up as discussed in the last blog, and create the conditions for the northward movement of the bay branch of the monsoon and a gush of the cross equatorial winds. It is still only 2 days since the passing of the cyclone, and the waters will heat up in a day or two, and maybe keep the date of monsoon over Andamans.

Sub-Continent Region: The region has started heating up exactly as anticipated.

Maximum temperatures on 4th.May

Nawabshah (Pakistan) 48°
Sibi (Pakistan) 46°
Jacobabad (Pakistan) 46°
Hissar Airport (India) 45°
Gwalior (India) 45°
Rohri (Pakistan) 45°
Kota Aerodrome (India) 44°
Amritsar Airport (India) 44°
Jharsuguda (India) 44°
Satna ( India) 44°

This list of todays (Sunday,4th.) maximum shows Nawabshah touching the 48c mark. And, the seasonal low has started to form, with the core at 998mb (IMD) today.A German forecast site shows the core pressure of the seasonal low dropping to 995mb. by Tuesday,6th.
However, the weak W.D. passing through the northern regions today may not bring down the temperatures to a large extent, except provide a relief of a degree or two, that too for one day.

Arabian Sea: The water temperatures of the region still are seen as below normal in the above image. But it is some time before this needs to heat up. Even if the waters heat up in the next 10 days, the Arabian Sea branch of the monsoon will progress on the normal date.
Yet again,it seems the monsoon can be on time and as per normal date.

Shall discuss the intensity and performance of the monsoon as per available data next week.

Thursday, May 01, 2008

Monsoon Watch-10
Bay Region: Severe cyclone "Nargis" is now moving away towards the Myanmar coast, and will hit the coast on the 2nd. Subsequently, the winds in the bay would take about 10 days to regroup back into pre monsoon formation as the bay water temperatures are now down to around 30c. Since, according to forecast models, the ridge aloft at 500hpa is moving away, the typical situation of strong south-westerlies from across the equator will be back into action near about the Andaman islands around the 11th./12th. The monsoon could advance into the Andaman Sea by the 14th.
Regions of south east Asia, and Thailand coast could get the monsoon rains from the 15th. Singapore and west Indonesia areas will get a spurt in rainfall activity due to the above reasons from next week.

Sub-Continent Mainland: The sub continent is now in for some severe heating in the next 10 days. From Kashmir to Maharashtra through Rajasthan, Delhi, M.P. and Gujarat, the days are forecasted to heat up . In Pakistan, the Sindh region will see temperatures go up to 48c in the first 10 days of May, and places in Rajasthan could see 47/48c and Akola or Nagpur may touch 47c. Gujarat may witness a 45c in a few places in the first week. This augments well for the formation of the seasonal low, which is forecasted to form around the 4th. by the NCMRWF. The weather is expected to be dry, except on the 3rd. when a weak W.D. crosses by and precipitates little rain in Kashmir.

Arabian Sea:With the developments, the ICTZ can cross the equator by the 10th. Subsequently. it will tone up the equtorial flow of south westerly winds in the Arabian Sea region, and the Somali current could strengthen after the 15th. The sea temperature needs to warm up still by 2c.
Hence Maldives and Comorin can expect the monsoon rains from 20th.