The first low of 2008 from the bay is now a named cyclone (Nargis), and as of Tuesday morning was a severe cyclonic storm of 65kts winds and core pressure of 986mb.
Presently at 13N and 85.5E, the forecast models expect the storm to move northwards initially, due to a trough over Bangladesh, but soon to recurve towards the Myanmar coast, as a high ridge to its east and the trough aloft, will steer it in that direction.
The outcome of the storm is that the cross-equatorial flow in the east (bay segment) has become strong and is being pulled towards the cyclone. In the west, that is over the Arabian Sea, the cross equtorial flow is getting organised, and is of normal strenght.
The northern sub continent region continues with high day temperatures, and the entire region is now in the 42-45c range (map), with 46c as the highest on the 28th. Conditions and settings are ready for the heat low to form.
I would like to compare this year's setting with 2006.
In 2006, a bay low had developed into a cyclone, Mala, around the 27th. of April. This intensified into a severe storm, and around the 1st. May, and crossed the Arakan coast of Myanmar. Winds from below the equator, in the eastern segment had intensified in the bay then too. In 2006, the northern belt of the subcontinent had normal day temperatures in April, and a severe heat wave during the first 10 days of May. The heat low was then formed around the 1st. week of May and a gradient created between the pressure of the Sindh/ Rajasthan region and Southern tip of India. After 10th. May, there were a couple of W.D.'s, and the temperatures fell in the entire northern belt for a week.
The Somali current, a forerunner of the monsoon a week ahead, built up around the 19th. of May in 2006.
And in 2006, the monsoon set in on 15th. May in the Andamans, on 26th. May in Kerala, on 31st. May in Mumbai and by 2nd. June over South Gujarat !
What do you think ?
vagaries© of the weather.blog written by rajesh kapadia.concentrating on meteorology of the Indian sub continent and extreme world weather since 55 years For Any Information taken from here, due credit must be given to Vagaries.
Tuesday, April 29, 2008
Friday, April 25, 2008
Starting with the Bay, there are indications from the IMD and ECMRWF and other international models of the formation of the 1st. pre monsoon low. This is forecasted to form end April, and could well turn into a depression. Not many models predict its movement into the coast of India. Rather all suggest it crossing the coast of Myanmar/Thailand around 3rd. May. This could well be true, as a high aloft in the region of central India, and with a clockwise circulation aloft across the east coast of India will prevent any system in the bay from moving westwards. The water temperatures in the Bay are around the normal levels of 30-31c. Both the above are reasons for holding the system from reaching the cyclone level. The first week of May is an "on schedule" date for the pre monsoon low in the Bay.
But the mainland continues to heat and the map from IMD shows a huge "above normal" region (though not a heat wave yet). Highest today was 45c at Akola(India) and 46c in Nawabshah (Pakistan). Though not yet formed, and at 1004mb today, the seasonal heat low over the regions of Rajasthan/Sindh could well form around the 1st. week of May. For this, more day and night heating is required, especially in the Sindh regions of Pakistan and Rajasthan in India.
Required to be ready by the end of May, the seasonal heat low should be (by May end) at 994 mb and stretch from Rajasthan in the east to Arabia in the west, with Jacobabad at its centre.
The streamline map shows the wind discontinuity to be firm now in the southern peninsula. The easterlies therein bring in the required moisture in the peninsula regions. The mentioned low is also seen forming in the south bay .
All indications as yet are for the monsoon to hit the Indian regions around the due dates. That is Andaman Sea around 16th.May, SriLanka by the 25th. and Kerala around 1st. June.
Tuesday, April 22, 2008
In the southern hemisphere, the low that has formed off the north-east coast of Australia, is now gaining strenght, and is poised to become a tropical storm. It may be a bit late in the season now for a storm to hit northern Australia (if it becomes a TC), as it may require the tropical rain belt (ITCZ) to hang around longer there. The satellite image from IMD shows the greater cloud mass shifting east, and the formation of the deep low.
As a result, the cross equatorial flow seems to be getting diverted towards this formation. Seen in the IMD chart, this diversion '' deflates" the momentum of the flow required to cross the equator. It will now have to seen how much this storm forms and gains strenght.
The northern/central heating of the sub-continent continues though, with Nagpur highest at 44c on Monday. ECMRWF and NOAA predict the formation of a low in the Bay around the 28th. But, ECMRWF also shows the low to move towards the Myanmar coast without gaining much. And the seasonal low in the northern plains is forecasted to form systematically by the 27th. at around 1000mb.
Sunday, April 20, 2008
Continuing from my previous blog about the southern hemisphere, the convective clouds linked to the MJO has moved eastwards as anticipated. The satellite image shows the convective clouds west of Indonesia. As forecasted, the clouding seems to be moving towards the south-east, and getting pulled to the north-west coast of Australia. A low has already formed there. Now, it is possible that the cross equatorial south easterlies, now in symmetrical formation, will twirl around this low by tomorrow. This will reduce the systematic flow heading towards the equator, and for a few days disrupt the smooth flow of the cross equatorial flows.
But this sequence has been anticipated in my blog of the 17th., and the date of the monsoon onset has been predicted to be near the shcedule date taking this event into consideration.
Meanwhile, even though the seasonal low in the Rajasthan region has still not organised itself, the northern/central heating is on, with Nagpur at 43.5c today, and Nawabshah at 42c. There is a W.D. approaching the northern regions of Pakistan/India. It has been predicted to be weak and effect only the northern most regions and not the plains by the IMD. I personally feel, that this W.D. may dip a little more than just the hills, as there is no organised trough in the peninsula to keep it in the higher regions. Also, there is no ridge aloft to defer any W.D.
Thursday, April 17, 2008
With the moving away of the W.D., the day and night temperatures on wednesday/thursday have dropped to below normal levels in northern regions of Pakistan and India. Substantial drops of 2-6c have been noticed in many places, notably Amritsar at 11c (-5c) and Islamabad at 10c as the minimum on the 17th.. These variations , I had thought would not affect the sesonal low formations. But, as Vinson from Business Line rightly predicted, the seasonal low has become "distorted", and now is at around 1002 and that too the core having shifted east of its normal position.
The required north/south trough has formed, and its initial position today is in the region of south Mah.leading southwards till south Karnatak.
In the South China Sea, the 1st. typhoon of this season "neoguri" is now off the coast of Vietnam. Forecast models predict its movement towards the south China coast, and may strike land west of Hong Kong. But, at this time of the year, and season, when the monsoon winds have not yet formed in the Bay, and the W.D.s are still "sort of" active, it is not possible for an easterly "pulse " to form from this typhoon and creep into the Bay. Any low forming into the bay now has to be "in situ", that is to form on its own by heating of the waters in the Bay. With the Bay still at 29-30c, it seems the pre monsoon low is still at least 8-10 days away.
In the southern hemisphere, the "power house" of the south-west monsoon, the mascrene highs, needs to form as an elongated high, at about 1025mb, from the coast of south Africa to a region west of Austrailia. This should be ready by the 1st. week of May to give a push the south-easterlies across the equator.Today there are 2 seperate highs in specific regions off the coast of south Africa, and west of Australia. But ECMRWF forecasts a fading away of the high off the Australia coast around the 24th. of April, due to the eastwards movement of an MJO. The result may be that the force of the south eastrelies heading towards the equator may diminish for a week. Also, the MJO may create a low off the coast of east Australia around the 24th. This may stagnate, for a week, the movement of the ICTZ.
Seems a bit difficult with these developments for the monsoon to be earliar than the scheduled date.
Monday, April 14, 2008
Monsoon Watch - 4
The day temperatures in the north Pakistan/India and central India regions have now reached the 40-42 c levels as of today. Today, 14th., the highest temperature in the sub-continent was 42c in Nawabshah (pakistan) and Rajkot (india). And with many places recording 40c -41c. as seen in the temperature readings today (Monday).
With the day temperatures now having risen in north/central India, and most parts of the country now 1-2c in the above normal range (chart above), the seasonal low has started forming. The low, of 1002 mb, is seen in the IMD MSLP chart as of 14th.
Heat wave conditions (5-6c above normal) are forecasted by the IMD around the 16th./17th. for central regions.This should be good for the further strenghtening of the seasonal low, and hasten its spreading westwards by the month end.
The line of wind discontiunity is also firmly in place now and runs from south Maharashtra down to the tip of India. With this in place, it has to stretch itself northwards, before being converted into a trough of low. The wind discontiunity will rush in easterlies from the bay, thereby bringing in the required moisture into the peninsula inland.
Both the developments are requisites of a pre monsoon scenario. But the bay requirment, formation of a pre monsoon low in the bay, is still laging, and may not materialise till the 25th. April.
With the "land part" development going on well as per schedule and fast, and the "sea part" possibly also ready by the month end, it seems the monsoon this year could be on time.
Thursday, April 10, 2008
Monsoon Watch - 3
1.-As a result of the W.D.,the day temperatures in the northern regions of the sub continent have been below normal throughout the first 10 days of April. In fact the rainfall across the border in Pakistan was heavy with many places geting rain amounts in excess of 50mm/day last week.
Another weak W.D. is scheduled to cross the regions of north Pakistan through to India on the 12th. April. It will cover the states of Kashmir, H.P., Uttaranchal and may not be very heavy in precipitating rains. However, the days will start to get hotter in the Sindh areas of Pakistan and the Gujarat,Maharashtra and plains of northern India in the next few days. But, I do not see a real "heat wave " coming in the next week. So, the formation of the seasonal low over north India/Pakistan region may well start to form after the 15th. At present the w.d.s are preventing the proper low from forming.
2-In the southern peninsula, the line of wind discontinuity is a bit disorganised. This needs to get organised again, and form into a trough (atleast by the 20th.), and subsequently, this trough remains till the onset of the monsoon, when it becomes horizontally east-west, and merges with the monsoon trough. Also, the wind discontinuity line needs to be proper by mid April, to bring "oft and on" thundershowers in the southern states to increase the moisture in the atmosphere.
3-In the bay, as the map shows, the sst are a bit below normal, in the southern seas. Needs to come to at least normal levels to form the pre monsoon low. I expect the temperatures to reach normal levels by the20th. And no major international model shows the formation of a low in the bay till the 20th.
All the 3 parameters above can get organised into proper formation by the 20th., which is the normal date for the sequence of events, and if maitained, may not delay the monsoon.
Another important factor,the monsoon thrust from below the equator too, needs to give proper support to the buid-up around the sub-continent. But the various parameters of the southern hemisphere need to be followed later, after the 15th. of April.
Saturday, April 05, 2008
Day temperatures today (Saturday) have dropped to 15c below in Uttaranchal and were 7-9c below normal over the northern region with a few place recording days upto 12c below normal. In Pakistan too, the highest tempearture in the country on 5th. was 35c, while we saw a high of 43c in late March there. In India, the highest temperature on Saturday was 37 c at Solapur and Anantapur, while most of the places in the traditional hot regions of the northwest were below 30c. Surely much lower than normal. It could be well over 40c at many places by this time.
The W.D. is now sliding away to the east, and can precipitate rain along its path in the next 2 days. A trough in the rear of the W.D. may form from Gujarat to inland Karnatak for a day on the 7th./8th. Resultantly there may be light rain in the western ghats region of Maharashtra (Lonavala and Mahableshwar) on Tuesday/Wednessday. Also light sporadic rain may occur on these days in Karnatak.
La Niña involves a cooling of the eastern central Pacific Ocean waters and the current episode began to develop late 2007. La Niña is now said to be weakening and the Australian Bureau of Meteorology reports that it is weakening ahead of previous model predictions. However, most model guidance is consistent in suggesting continuation of La Nina conditions [as indicated by central Pacific SST] until around the end of the southern hemisphere Autumn. This is the time of year when abatement of La Nina conditions would typically be expected. Status of the La Nina should be watched for the next 30 days to see its effect on the monsoon, if any.
The diminished MJO activity is diminishing along the North Austrailia region, thus showing the first real signs of the ICTZ to start moving from its southern hemisphere base.
Friday, April 04, 2008
The anticipitaed W.D has started dumping rain/hail almost all over Pakistan and in north/nortwest india including Gujarat on Friday.
In Pakistan, southern cities like Karachi had rain and rain was reported throughout Sindh and northern regions. Traditional hotspots like Jacobabad and Sibi had a high of only 28c.
In India too, the weather changed on Friday in Rajasthan,Gujarat, M.P.,and all the northern states. Temperatures fell to 11c below the normal in places like Bikaner in Rajasthan, and were below normal by almost 6-8c in many other places in the region.
With the passage of the W.D., the rains will continue for 2 days, and the temperatures will continue to remain low .
What happens now to the monsoon set up ? The NCMRWF has predicted a high pressure of 1012mb forming over the regions of central India and adjoining areas on the 7th. Later it shows the high dissolving in a day and the pressure in the region hovering around 1010mb for the next 2 days.
If this happens, the temperatures can drop a bit more in the north of the country on the 7th and 8th. and nights may even go down to 12/14c in some places. And, initial start up of the seasonal low around the areas of Rajasthan may then resume only after the 11th.
The strong wind flow from the W.D. has slightly "distorted" the line of wind discontinuity in the south. The map shows the "line " having moved a bit northwards, or, a bit "broken up" in the extreme south. As this current W.D. is expected to trek through northern M.P. into east India, the winds in the south could re-establish around the 8th./9th.
This is as far as the low formation over the land is concerned. For the pre monsoon low over the bay, I do not see any low forming till the 12th.( normally low could be expected by 15th.). Bay sea temperatures today hover a little below 30c,(map alongside), and, and the absence of cloudiness, it may warm up in a week to the required level.
Hence, the initial pre monsoon lows required to be formed over land and sea, can, still start around the normal scheduled dates, that is mid April.
Wednesday, April 02, 2008
Monsoon Watch - 1
The setting for this year's monsoon seems to be slightly slugglish. What should be normally seen is a rising trend in day/night temperatures, especially in northwest India, Pakistan and central India. But, with the advent of 2 W.D's in the north, the temperatures are set to fall by 2/3 c, and return to below normal levels in the concerned regions. In fact the minimum temperatures of several towns in Maharashtra are already 5/6c below the normal, with Mahableshwar at 12c (-6c).
The W.D's will be precipitating rains in the northwest and Rajasthan regions from 3rd. through 6th. April. The upper air trough (of the W.D.) is forecasted to dip right down to the 20N level. Thereby, rains/hailstorms could be expected northwards from north Gujarat and along north M.P., besides the other northern states from the 3rd. to the 6th.
This will, for now, halt the creation of the monsoon low, normally expected to start forming around Rajasthan/Sindh region by the 2nd. week of April. The pressure at sea level today in the area is 1006/1008 mb.
On the seas temperature section, the anomoly map shows the northern Bay to be a little above the normal. While the southern seas both sides of the Indian peninsular is below normal. And that is the region we are looking at for the formation of the pre monsoon low in the Bay.
The persisting line of discontinuity in the southern tip of the peninsular is the "plus" point, as it can develop into the required trough in the region. The trough in this area is required as it helps in the quick formation of a low in the Bay (as and when ready to form).
Hence, forming of the "pre monsoon" conditions, both, around the Rajasthan/Sindh region, and the Bay, is not expected to resume before 8th., at least.
Initially, it translate into the fact, that, the monsoon cannot be earlier than the scheduled date. Monsoon can set around the normal date. At least that is as the situation stands today.
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The low, has literally "whizzed" past,and thru the central regions, and by saturday night, is already over south Rajasthan/Gujarat...