Sunday, May 31, 2009

Monsoon Watch-15

There is almost no change in the situational forecast in the 2 days since by blog of the 29th. And, the outlook and anticipated weather developments for the next 10 days remains the same, and is maintained, as mentioned in the blog of 2 days earlier.

From the 1st. of June, rainfall (pre monsoon ) will creep up northwards along the west coast of India, and keeping the inland peninsula devoid of any meaningfull rains for the first 8/10 days of June. The eastern coast will remain practically dry. Bangalore can expect a thundershower on Monday/tuesday, but dry thereafter for at least a week.

Due to the W.D. changes mentioned below, the actual monsoon , I feel, will start advancing north of Mangalore and into northern Karnatak, including Bangalore, on or after 5/6th. June.

( Another W.D. is forecasted to enter northern India on the 4th. June, and I feel close observations of this sysrem is required).

The W.D. (low aloft), now passing thru Northern India, has resulted in a drop in temperatures. The day temperature in the map alongside of the 31st. shows substantially low days in the U.P. region. The anomoly map shows the picture of the day clearly.

Higher reaches of Utterakhand and H.P. had snow on the 30th.
However, it was very hot in the southern regions of Sindh, with Turbat reaching 52c today.

Friday, May 29, 2009

Monsoon Watch-14

Carrying on from last blog's Monsoon Watch-13, call it a "false start" or a weakening, the monsoon is now at its weakest ebb today (29th.). But I would not worry much*, as it was anticipated to happen, with the W.D. "low aloft" taking hold of the northern regions of India. Surely this is only for a couple of days, and again I feel the monsoon current will start creeping up north along the west coast after the 30th. of May.
Initially, the coastal regions of Karnataka will get the rains, and the first pre monsoon showers wetting the Konkan region after the 1st. of June. Pre monsoon showers can be expected in Mumbai from Tuesday night, continuing almost daily, with increasing intensity, till the actual monsoon. Monsoon can set in Mumbai by the 7th./8th. June.

*I maintain, the parameters are conducive for the advance, and except for the lone W.D., there is nothing negative to cause concern of advancing flow of the monsoon current.

But, till the 10th. of June, I feel the interiors of the states of Maharashtra and Karnatak will be devoid of any real meaningfull rains. The monsoon may penetrate inland after the second week of June, as there is no real system predicted in the Arabian Sea till then. Also, a low is anticipated in the bay by the first week of June , and its effect inland, by the second week only.
Resultantly, a heat wave, in patches, with temperatures in the 45-47c range, can be expected in Rajasthan, Delhi, M.P., Chattisgarh and Vidharbh in the first 10 days of June. Minimum night temperatures can be as high as 32-34c .
Across the border, it has touched 50.4c in Sibbi and 50c in Turbat in the last 2 days.

Tuesday, May 26, 2009

With the cyclone system having moved out of the way, the monsoon should re-group now again.

As per the mentioned in the Monsoon Watch-10, in paragraph 3, the clouds of the monsoon system have now started forming in the central areas of the Arabian Sea.

Subsequently, these cumulus clouds should now start rolloing towards the west coast.

And accordingly, the monsoon can be expected on the remaing regions of the west coast, that is coastal Karnataka and Konkan in 6/8 days from now.

Sunday, May 24, 2009

Monsoon Watch-13

As discussed in the last blog, the result of the initial gush of the south west winds in the Arabian Sea towards the deep depression in the bay , has resulted in the monsoon setting in over Kerala on the 23rd. of May. 8 days before the due date !

BUT, let 's see what todays streamline map indicates: It shows a strong south west monsoon current, just south of the tip of India. Over the state of Kerala, today, it is not as strong as it was yesterday. The "pull" of the winds towards the newly formed cyclone is effective south of the Indian coast. In fact, international weather forecasts predict a reduction in the intensity of rain over Kerala from the 25th. for the next 3/4 days. After that, say from the 28th, regrouping of the monsoon current may take effect, and the monsoon can subsequently progress along the west coast northwards. And, today (24th.), the reduced effect is already seen, with Kochi recieving 8mm of rain and Thiruvananthpuram 3mm. only !
It could well be a "false start", in Jim's words.

Meanwhile, the deep depression in the bay, has intensified in to a named cyclone, "Aila".
It is expected to intensify further, and cross the W.B./Bangladesh coast by the 25th. night.
It should pull up the monsoon upto the northern fringes of the bay within the next 2 days.

As mentioned, I repeat again, after crossing the coast, the cyclone will weaken, and then allow the Arabian Sea south-westerlies to re-group.

Re-grouping (after the 28th.), may not take long, as the necassary parameters are already in place. The pressure gradient is enough today, the heat in the Sindh/Rajasthan region is sufficient, and spreading westwards, and the seasonal low is firm with a core of 994/996mb.

Friday, May 22, 2009

Monsoon Watch-12

The latest development :
Weather advisory from he JTWC:


The situation is flexible now !

The streamline map shows the winds getting sucked into the circulation, and with the system getting stronger (forecasted to become a depression), the winds from the Arabian Sea are likely to get totally diverted towards the circulation. This diversion may occur till the system moves away northwards, at least above the 15N line in the bay. That means the strenght of the winds along the west coast are likely to diminish, and consequently the clouding, during the next few days.

The ECMRWF forecasts the depression as moving north, and hitting the Bengal coast by the 25th./26h. So, till then we have a sort of "diminished " monsoon activity along the southern parts of the west coast.

The monsoon , as a result, will move up the bay along with the system. The pressure chart from the Thai Dept shows a monsoon trough has formed joing the depression and the low in Thailand.

The seasonal monsoon low over the desert regions of the sub-continent is well entrenched, and the core getting deeper(994mb). The temperatures in the Rajasthan/Central India/Sindh region are around the 44-47c range. The highest in India being 47c. The nights are very hot in the Rajasthan region, with Jaipur seeing a LOW of 33.6c on Friday.

Meanwhile, the peninsula regions of the souh and interior Maharashtra continue to recieve pre monsoon thundershowers. Effectivly, this has kept the nights cooler around the normal to slightly below levels in the region. See map showing the "cooler" regions.

Now, this summerises to the conclusion, that in the next 4/5 days, the monsoon will forge northwards towards the north-eastern states of India. should arrive there by the month end or before.

Along the west coast, a delay of about a week ,after Kerala. A low is forecasted by some international models in the Arabian Sea on the 1st. of June. If held true, it may be an instrument to pull the monsoon north along the coast.

Tuesday, May 19, 2009

Monsoon Watch-11

This streamline map of IMD shows a perfect development of the south-westerlies in both, the Arabian Sea and the Bay segment. The picking up of the wind speed in the Arabian Sea segment, near Sri Lanka and southern region, is due to the increase in the gradient in the pressure, as the monsoon low gets estabished in the Rajasthan region. The heat is prevailing in the "core" area, as seen in the map.

Now, the winds and cloud formation in the central sea is bound to gain in strenght, as the Somali Current is prevelent. This is seen in the commencement of the water sst cooling off the Somali coast.

Resultantly: Pre Monsoon thundershowers have started rumbling along the southern parts of the west coast of India. Karnataka and interior Maharashtra also have started getting pre monsoon thundershowers. This "pre monsoon thunder" precipiation will continue in coastal /interior Karnataka, Goa and Kerala, till the actual monsoon current advances into Kerala around the 27th./28th. of May. Before that, the monsoon will progress into Sri Lanka around the 23rd. From there, after hitting Kerala, the monsoon's advance needs to be monitored, as there are some indications of the progress slackening a bit.

In the Bay, after an initial delay, the monsoon has again started progressing towards the south islands. The normal date for the monsoon in the south islands is 20th. May.

Thursday, May 14, 2009

Monsoon Watch-10

Super speed fast developments on the monsoon front prompts me to write again today.

1. As discussed yesterday, the heat has spread eastwards into Rajasthan, India, and, as the map shows, one station in the state (Kota) has touched 47c and some are at 45/46c. The highest in Sindh today was 49.6c at Nawabshah.

Now, as per yesterday's explanation, the heat will creep into the central and eastern regions of India from tomorrow.

2. Almost, as if in response, the monsoon low has deepened overnight. Today , it had a core of 996mb, in exactly the region it is supposed to be in. All that is required now is for the low to deepen more to around 992-994mb. and elongate westwards.

3. The south-westerly streamline from below the equator has reorganised itself, almost to perfection. With the ITCZ moving up, the formation of cumulus and cumulo-nimbus clouds in the Arabian Sea (always starts there in the central sea region), should be a week away from today, that is by the 20th. From then , the clouds roll towards the coast of Kerala as the sst starts heating up near the coastal areas, and in another 8 days should pour the monsoon rains over Kerala.
Coastal regions of Kerala should see an increase in rainfall from 19th, when the pre monsoon thundershowers can start. Coastal Karnataka can get its first pre monsoon thundershowers from the 20th./21st. Bangalore, should see pre monsoon thundershowers on the 21th./21st, as a result of the rain bearing clouds penetrating inland from the Arabian Sea.

IMD has issued a bulletin today forecasting the monsoon to be over Kerala around the 26th. +or - 4 days.

If things develop from today as per the normal "progress rate", without any "disturbance", the monsoon can be over Kerala by the 28th/29th.
All the cities along the west coast will start getting humid and stuffy , with the warm south-westerlies gaining speed. Mumbai will see increasing humidity levels, with warmer nights.

4. Meanwhile, in the bay segment, the south-westerlies are on schedule, with the speed picking up and the sst maintaing at around 31/32c . The monsoon should be hitting the south Andaman islands in 2 days. If this segment maintains its progress, the north-east states should get the monsoon rains by the 1st. of June.

Wednesday, May 13, 2009

Monsoon Watch-9

The actual progress scene of the south-west monsoon is hazy and unorganised to some extent as on todays synoptic situation.

1. While the ICTZ has moved north a bit, and is roughly around the 2N line now, clouds are seen along this line and a band stretches from south Arabian sea to south of the bay. this is seen in the wind direction just above the equator, south of India, in the streamline map. The two maps can be compared.

The north-westerlies from the Arabian Sea along the western region of India curve at the tip of the Indian peninsula and blow as southerlies along the east coast and as south-westerlies into the south Andaman Sea. But this is a result of the trough / wind discontinuity at 0.9 km a.s.l. from Jharkhand to south Tamil Nadu now running from Chattisgarh to south Tamil Nadu through Telangana and Rayalaseema.

Now, this trough has to fizzle out to allow the monsoon to gain current in the south bay. International models now predict the rains, and wind to strenghten in the south Andaman Sea from the 17th.

2. Extreme heat wave conditions are to repeat high temperature readings in the northern belt of the sub-continent from tomorrow, the 14th. Rajasthan readings are likely around 46-48c in the next 2 days and other heat wave prone regions like Vidharbha. Heat is then likely to spread to the east. 3 stations in Sindh have recorded 50c today including Larkana and Jacobabad. This is due to the high "aloft" today over the Sindh region, and which is expected to cover a larger area eastwards from tomorrow, as a result of which the heatwave will creep into India.

The monsoon low which has started forming in Rajasthan a few days ago, still has the core pressure remaining around 1000mb. Now, this monsoon low has a long way to go, with the core presuure area to ultimately be at 994mb, which should elongate and spread westwards into the Arabian region.

Saturday, May 09, 2009

Monsoon Watch-8
Things have ''sobered" down to some extent after he movement of two consecutive W.D.s in the north. The systtems have brought relief rains in most of the northern states. Another W.D. is approaching

Even todays day's highs as seen in the map are almost on the normal levels. A 45c high at Nagpur, and a 47c in Sindh. Yes thats high, but near normal levels.

As a result, the seasonal low over the central regions of the sub-continent, which should be forming by now, is a bit tardy in its formation, and the MSLP map from IMD does not show much progress in the formation.

But, a line of discontiunity along the south Maharshtra, Karnatak an Kerala line, has resulted in the convection development of thundershowers along the axis of this line. Thundershowers, with hail, was recorded in Mahableshwar on Thursday and Friday. Pune too, got some rain on Friday. These "pre-Monsoon" showers mean well, as some moisture has started accumalating in the peninsula. ( This is the result of the 2 air streams from the west and east meeting along the lone of wind discontiunity).

Below the equator, the winds are all "geared up", and are already south-westerly in the bay segment. And picking up speed ! The picking up of speed indicates gathering more moisture, and forming rain bearing clouds. Also, the ICTZ, as seen in the streamline map, is now exactly over the equator, and is poised to cross the imaginary line on its due date, 10th. May. SST is around 31c/32c in the bay now, ideal for the cumulus cloud formation.

Thus, with the above two indications, the monsoon is all poised to enter the south Andaman Sea, around the 13th./14th. Thus, for the bay segment, the monsoon seems to be on schedule.

Saturday, May 02, 2009

Monsoon Watch-7

Come a W.D. and there was relief from the blistering heat sweeping most parts of the sub continent on Saturday. Relief meaning the temperatures did drop by about 2/3c, and bringing it down from +6c to +3c, but still remaining above normal. Better, after the 50 year April high in Delhi at 43.5c on the 29th.( Palam was over 45c), and another April high in Dehra dun at 41c, and Simla at 28c. Nagpur too set an April record at 47.4c on the 30th. and Khandwa was the highest in the Indian region with 47.5c recorded on same day.
The heat wave has resulted in the forming of the seasonal low over the Rajasthan/sindh region. The surface map shows the low at 1000mb. With the formation of the monsoon low over the landmass of India, the process of the "monsoon build-up" has begun.

In the southern hemisphere, the south-east winds have "almost" established themselves as of today, and are, in about a week, set to take the south-west turn after crossing the equator. This always starts in the Bay sector first. For this, the northward shifting of the ITCZ above the equator is a must. The ITCZ today is at around 5S.

Forecast models estimate a MJO wave from the 10th. of May. An MJO positive wave will surely carry the ICTZ above the equator around the 10th, which is the normal date for it to cross the imaginary line. Even the sea temperatures in the bay are now conducive for this development. (see map).

South-west winds can commence over Kerala from the 7/8th. onwards, and may bring some precipitation alongwith.

The forecast map from NCEP shows the strong rain current (monsoon) approaching the Andaman Islands between the 11th. and 18th. May.

Meanwhile todays W.D. has brought some welcome rain to the northern parts of the sub continent, and the Orissa state, which has been under severe heat. This W.D. will move away in a couple of days.

Monsoon can set in over the Andaman Islands around the 12/13th. of May.