Sunday, June 29, 2008

On the South Asian weather front, the situation is variable as on today..
From the western end, there is the normal summer heat of 48c in S.Arabia, and 46c in the U.A.E. But the temperatures have dropped a bit in the Oman region.
Eastwards, Pakistan is having rains in the north, due to the western end of the monsoon trough holding on, and dry in the central and south. The highs in the Sindh region is around 43-45c.
Moving to India, the heavy rains persisted in the Punjab, H.P.and west U.P. areas and also in the eastern regions of U.P. and Bihar.
The monsoon trough is along the west U.P /north M.P. and Bihar line.
However, the extreme western end of the trough (seasonal low), now over north Pakiastan, should have, by now, gradually moved towards the west into Baluchistan and into the Arabian region. On this happening, it would have been difficult for the trough to stay and get hooked over northern India, and could have moved south. The seasonal low can even now, with the exrteme heat in west asia, creep into the west asia region and stretch the "trough end" away from the subcontinent.Much needed rains could then commmence over southern areas of Pakistan and the monsoon could cover all of India.
A ray of hope for the state of Gujarat. An upper air circulation has appeared over the north Arabian Sea, off the coast of Gujarat and north Maharashtra.
Forecasts show this system to move inland into Gujarat in 2 days, around the 30th./1st. Hence, some heavy rains could be expected in coastal Gujarat, and regions of Rajkot, Surendranagar, Ahmadabad and eastern Gujarat areas on the 1st. Similarly, some heavy rain could also be expected in north Maharastra coastal regions.(western ghats hill staions will get some heavy rains, ranging from 100-150mms in the next 2 days).
The estimated forecasts do not indiacte the system to last for more than 2 days.
Hence the rains due to this system may be short lived and may last for 2 days .

No low is forecasted to form in the Bay for another 2/3 days atleast. Hence the interiors of the peninsula areas will continue to remain dry into the first week of July.

Friday, June 27, 2008

The latest rainfall distribution map says it all.
As on the 27th., the all India rainfall map on the IMD site shows the excessive rain areas in the north along the "monsoon trough line" of which I have mentioned in the last few blogs.
And, the deficiency has started creeping southwards, taking the inland path.
Well, this picture was anticipated and foreseen all along, what with the monsoon trough hugging the Himalayan foothills,almost immediately after setting in almost throughout the country.
Last weeks' rain is seen in the map of the week's rain at IMD, and the rain excess region is seen along the trough line. The remaining areas south of M.P. have had very scanty rain during the week.
Reports from Maharashtra show the situation getting seroius, specially in the interiors, with the Marathwada region ( I had previously mentioned Aurangabad as a scanty rainfall area) showing a deficit of 61% !
Kerala, another seriously deficit state, has effected power cuts from 27th.
Now what for the next week ?
The low mentioned in the last blog in the Bay did materialise, and soon shifted into the north bound monsoon trough. It lay today as an upper air circulation, and is pouring rain over...yes..again over north M.P.,Chattisgarh,and parts of Delhi and, H.P. and Punjab. Thus leaving the dficit regions quite dry.
With no more lows forecasted till the 1st of July, I do not see the trough shifting drastically to its normal position till the 1st. of July. Hence no major shift in rain pattern southwards from M.P. downwards can be expected in the next 4 days.
The same pattern of rain, north bound, should continue over Pakistan too.
I give a cautioned forecast of 4 days this time, as it is hoped, that even without the formation of a low in the Bay, the monsoon trough can at times shift back to its normal position in the "peak monsoon season time" that is the first week of July.

Western Ghats stations of Lonavala and Mahableshwar may not see any substantial increse in rain till 1st. July at least.(Lonavala my get about 15mms of rain/day anf Mahableshwar may get around 25mms /day).

Meanwhile, in Oman, severe heat has brought temperatures in the 45-47c level in the last 2 days, with Muscat touching 47c today, 27th. Heat is expected in the Oman and U.A.E. regions in the neaxt 4/5 days.

Sunday, June 22, 2008

The last 7/8 days has seen the monsoon trough lying north of its normal position. It has been almost hugging the foothills of the himalayas, and on 2 occasions during last week, had mid level lows embedded in it. The western end of the trough has been fixed in the north Pakistan hills and running through Punjab,U.P. and down the states of Jharkhand and Bihar into the northern bay.
The result:During the week, excessive rains in the Jharkhand,Orissa and Bihar regions. Good rains in the northern states and Rajasthan and M.P. and north Pakistan regions. But, comparitively dry in the areas south of M.P. Deficiency has started to show in Marathwada,south Gujarat,north Karnataka and Kerala.
The wet spell in the excessive regions has lessened and the region is recovering from the flooding.
But the regions of Gujarat, Maharashtra, Karnataka,Kerala and A.P. are in dire need of the rains now. In fact, barring the coastal areas, the interiors of the west coast states have not yet had a decent rain shower. ( take for instanceAurangabad, has had only 18 mms).In Mumbai, though the total rain is 635mm, above normal almost double, it has had only" 8rainy days" out of the 22 days of June.
The situation as on Sunday night is that the monsoon trough is still in the "more than normal" north position. The embedded lows are weak, and thus the rains in the trough areas will also lessen in the next 2 days. But with this trough anchored there, it is not going to help the western and southern states.
What is needed now is a low in the bay to bring the trough to the central India regions, and bring back the precipitations southward. With a low in the bay, the monsoon trough comes back to its "natural" position.
IMD, and some other models have forecasted the formation of a low in the bay around the 25th./26th. Another low in the upper atmosphere is forecasted by some models in the north Arabian Sea, off the Gujarat coast. If this Arabian Sea low in the 500mb. level does form, it will be a boon for Gujarat and coastal/northern Maharashtra.
But events and dates are forecasts by some models, and some models make no mention of either low.
Eventually we will have to wait and see the reality.
I personally see the bay low forming around Thursday, and bringing rains to east A.P. first, then interoirs of A.P.,Maharashtra by Friday. Konkan and west coast may get increased rains from Thursday as a result of the low forming. Gujarat may have to wait to see the direction of the bay low, or the formation of the mid level low near its coast.
Coastal regions of Sindh,Pakistan can get its monsoon rains on the formation of the Arabian Sea nmid level low. Otherwise it will have to monitor the movement of a low in the bay.

Wednesday, June 18, 2008

The monsoon has jumped and raced into Delhi well ahead of schedule, 15 days early after 108 years. Thats all ok. But the "break monsoon " conditions for the central/south peninsula and western region, discussed in the last blog, has occured.

The depression formed in the bay rushed off in the north/ northwest direction and as a result poured heavy rains in Bengal, north Orissa, east U.P. With the monsoon trough well established along the foot hills , the "break monsoon" has been created in the central, western and southern regions of the country, which have recieved very negligible rain in the last 2/3 days now. The image shows rain of Tuesday, and check the areas where it is concentrated. Totally avoiding the regions in the west/south and central, typical of the break conditions.

Now what ? Now we have to watch the movement of the depression. 1.) As it fizzles out, it may move north/north-west. In that case, the break in the areas mentioned may be extended till the system is fully drained out. That normally takes around 5/6 days.

2.)On the other hand, if the system drains out fast,in a day or two,, without moving, and static over the current position, then in 2 days the monsoon trough can shift down to bring increased rains back to the "break" regions.

The situation will have to be watched. Situation 1.) is typical of early monsoon stage, and 2.)of mid monsoon period. I have no comments or forecasts, but the first situation is not desirable now, because as explained in the previous blog, interior areas of Mah./Karnatak,Kerala and parts of Gujarat/M.P. need the rains more.

Saturday, June 14, 2008

Monsoon Watch-24
The monsoon in the sub continent has suddenly progressed fast and covered up most parts of northern India and touching Pakistan along the coast, sparing only the western region of Rajasthan and Punjab.It has reached the Pakistan border, both along the coast and in the northeast. This overall progress for the region is about 2 weeks ahead of schedule. The trend favors earlier than normal onset of the South West Monsoon over the central and northeast of Pakistan.This is the result of the unprecented low discussed in the last blog.

Hence here today, the South West Monsoon is underway ahead of schedule over the Subcontinent. What is now lacking is any well-marked Monsoon low--over Bay of Bengal; or over the Arabian Sea. Rather, what we have is a upper low just over northern India.
Persistent weak low pressure over northern India is shown by numerical forecasts to loiter for at least a few more days--this will uphold the pattern of scattered heavy falls over the open plains to the Himalaya foothills. This may lead to a "break monsoon " condition, which may not mean well at this early stage of the season.The trend favors earlier than normal onset of the South West Monsoon over the northern areas and northeast of Pakistan. Personally , I may not comment as to whether this is a steady trend or only a "jump" to be followed by pause or even "break monsoon".

Thus, close observation, and anticipation, with respect to the next few days will be for a moderate monsoon low over the northern Bay. Such a low, preferrably a depression, would alter and likely boost overall rainfall over eastern and northeastern India.This would also give a momentum to the now much required rains in the interior areas of Maharashtra and overall central/south peninsula regions.

Weak, ill-defined low pressure, aloft, over the Arabian Sea will continue the occurance of fairly good rains along the Konkan coast and rain along the Gujarat coast for a day or two. "Rain shadowing" will keep most of the inland regions free of any major rain. Rainfall on 13th. June is shown in the image.Concentration is mainly in the belt running north to east and along Gujarat/Maharashtra coast.

In some other related news, the monsoon rains have been exremely heavy in Hong Kong. On the 7th. of this month,the city Observatory recorded 145.5mm during the hour from 8am to 9a.m. the highest hourly rainfall since record began. From midnight until 6 p.m., 304.8mm of rain fell at the Observatory, the fifth highest daily rainfall record in June. Streets across Hong Kong were severely flooded, some roads were closed and some flights were delayed at the international airport. Mumbai cannot complain of getting disoriented by more than 100mm of rain in 24hrs !

Thursday, June 12, 2008

Above streamline of Wednesday shows a slight change from the expected. A low has descended from the upper atmosphere at almost MSL over the central India region. A trough from this low runs thru the northern region of M.P. and thru the central areas of eastern India into the bay.
As a result, rains were reported today, Wednesday, from central India stations and from Bihar.

Result: The monsoon will progress soon from the eastern side into central India, that is Bihar and adjoining Chattisgarh and east M.P.

The low has attracted a strong wind current towards it from the Arabian Sea, creating a south-west flow exactly over the Mumbai area. Thus, the inflow of extreme moisture has brought heavy rain to Mumbai( not forecasted) from Wednesday evening. Being an "in situ" low, it should vanish in 2 days, thus bringing respite to the metro city only 24 hrs. hence.
This is the major change/development from yesterday's forecast.

Otherwise, rains are moderate along the Karnatak coast, and the interior regions of Maharashtra and Karnataka did not have much rainfall.
The low off the Oman coast has fizzled out after precipitating some rain in the south of Oman and a light drizzle in Muscat as informed by a reader. Muscat should be cloudy till tomorrow, but it will be clear and back to 40-41c by Friday.

Wednesday, June 11, 2008

Monsoon Watch-23
Another well marked low has appeared in the Arabian Sea, west of the Gujarat coast. The system has since moved west, and latest as on 10th. night lay just off the Oman coast, with deep clouding very near Oman. Suspect system is likely to persist off the Oman coast for a day, before fading out. Some rain is likely on the south Oman coast, and light rain in Muscat area on Wednessday.

But this system, like the prevoius one last week, has again pulled away the monsoon current , though temporarily, from the west coast of India. The sudden spurt of rain, and quick before time monsoon advance along the west coast upto south Gujarat coast will be halted for a few days.
Hence, there is possibility of some let up in the rains, for next 4/5 days, in the Konkan region and coastal Gujarat. Due to the slowly building up low pressure in the mid Bay region, moderate ains may still continue in the coastal areas of Karnataka.
But the bay low seems to be taking its time to form. It seems from forecast models, that the proper formation of any system in the bay may still take another 4/5 days from today. Also, a trough running across central India through M.P., has brought rain across the region in the last 2 days.

The result of the above situations:

1. A weakening of rainfall in the monsoon areas of Konkan (Mumbai can breathe a bit) for the next 5 days. Weak rains in the deficient Kerala region and interior Karnataka in the same period.

2. Halt in the further progress in monsoon towards Gujarat, again for atleast next 5 days.

3. Still no monsoon rains in the "yet to arrive" regions of interior Maharashtra.

4. Due to unseasonal rains (W.D.'s) in the northern belt of India/Pakistan in the last few days, actual monsoon advance may be halted towards north as low and below normal temperatures prevail over the entire northern sub-continent. Some isolated thunder showers expected in Sindh coast region around Karachi on Wednessday, due to the Arabian Sea system.

5. Eastern areas of bengal, north-east and Orissa remain bereft of real meaningfull rains. A proper "systematic monsoon rain" over Kolkata and the bengal areas has yet to occur, though time wise it is not late as the monsoon normally sets in around 10th. June.

For the next major revival and northwards push of the monsoon, the bay region has to be obseved, as the low developing there seems to be taking its own time. No international forecast model shows any system there till 16th. June. The silver lining is that IMD has forecast a low off the east coast, near Orissa, in the next few days.

Saturday, June 07, 2008

Monsoon Watch-22

A brief write up on te developments in the sub continent in the last 2 days( since the last blog):

1. The suspect system in the Arabian Sea is fizzling out. It "graduated'' to no more than a depression, with some rain in south Oman.
As a result, the monsoon winds in the eastern seas have regrouped faster, and within a day, the monsoon current advanced into the Konkan, including Mumbai. The monsoon, as per my estimate, has advanced upto Dahanu in the Konkan region, and south madhya maharashtra in the inland regions as on the 7th. of June. Thus putting Mumbai city into the "monsoon area" on the 7th.
The cross equtorial flow is in full swing , and gusty winds are likely to strenghten the monsoon over Konkan in the next 2 days. In fact, with a low in the 500hp level predicted over north Konkan on Sunday (8th. June), I estimate very heavy rain over Mumbai on Sunday/Monday. Maybe around 100mm to 125mm in a 24hr. period.

2. The pressure gradient has also become favourable for the above development. The seasonal low over the Pakistan area is now at 996mb and the tip of Kerala is 1008mb. Good enough for the monsoon thrust.

3. And finally, I suspect a low to build up in the south Bay by the 7th. or 8th.and deepen into a depression in the susequent 2/3 days. This will also help pull up the monsoon along the east coast, as well as bring more precipitation along the west coast. Thus, if the bay low develops by Sat/Sun, we should see more rain in A.P. and coastal Karnatak/Maharashtra on Sunday/Monday. The actual mobement of the system will then be followed for further forecasts.

Thursday, June 05, 2008

Monsoon Watch-21
Let us carry on from the last MW -20. The monsoon movement is, surprisingly, as predicted.(If one can recollect, the monsoon was most unpredictable and erratic last year!).

After advancing into Kerala, it has moved up the Karnataka coast in the next 2 days, and the northern limit was at Goa as on the 2nd. Now for the tardy advance. It has reamined weak (or a feeble current as I always say), and this is shown clearly by the poor rain fall in the image. The image is of the day's rain on the 4th. and all the monsoon areas along the west coast are in the "blue shade", that is less than 10mm rain !

The rain in the northern region has stopped as from the 3rd, finally!-The graph of Delhi for May shows the lack of summer heat throughout the month. The average May temperature was 2.5c below.

However, since the last 2 days, the heat in the northern areas of Pakistan/India has now achieved the average norms, but still no heat wave. Not enough to really pull up the monsoon in the next few days. Core of seasonal low is still at 1000mb.

Another disadvantage is the low level circulation that has formed in the Arabian Sea. The "LLCC" today was around 450Nm south west of Mumbai. I call it a disadvantage, as , even though the cross equatorial flow is now good, all the moisture bearing winds (and clouds) will swirl around the circulation, and not move into the west coast of India. Thus, for another 2 days, the "lull" in the "monsoon advanced regions" can continue. Only to regroup, and push the monsoon again northwards into Goa and Konkan (and Mumbai) after 3/4 days. So we come back to our original date for Mumbai, around 9th. June !
The mentioned LLCC, according to the JTWC, has a "fair" chance of becoming a cyclone. One is not sure of this, as the Arabian Sea has given the "cry wolf" call thrice this last 15 days. But in any case, some intensification of the system will surely precipitate moderate rain along the south Oman/Yemen coast by the 7/8th. June.

Sunday, June 01, 2008

Monsoon Watch-20
The situation today, 31st. is exactly as per the forecast in MW-19. 2 days after Sri Lanka, the monsoon has touched Kerala on the 31st., and declared by the IMD too. Now, I repeat, the monsoon is weak, and should cover up the Karnatak coast in the next 2 days as a weak current.

Now, regarding its further movement northwards along the west coast, I maintain the stand that it will be tardy till the 7th.of June. A weak W.D aloft is still raining sporadic showers in the north Rajashtan/Punjab/Delhi regions. The image shows the rain areas on the 31st.May.

The 200hpa jet stream is seen moving slowly north by almost all the forecast models , after the 4th. Also now, with the heating taking shape in the northern regions (though not to heat wave levels yet), the seasonal low has started forming and dropping anchor near the Pakistan/India border.

COLA forecast shows a big "burst" of pre-monsoon thunder shower activity around Goa on the 3rd. The GFS forecasts also show pre-monsoon rain /thunder-showers creeping upto Mumbai by the 6th.

That withholding, it can be estimated that the monsoon can reach Mumbai as per MW-18 estimate date of 9th.June.

In the bay, I see the monsoon current dormant for another week. I had estimated earlier, that any activity in the bay would not reveive till after the first week of June. Well, the sst in the bay is still below normal, except near the head of the bay. On further heating of the waters we can expect some system to develop. Without a system in the bay, any major monsoon thrust is difficult. At the most, as the cross equatorial flows in the bay are strong enough even today, we may expect, again, a weak monsoon movement northwards from the bay islands towards the north-east around or after the 3/4 June. Kolkata can expect the monsoon only after the 9th.