Wednesday, October 29, 2008

As anticipated in the last blog, the lull in the rains has commenced. The cyclonic storm moved into Bangla Desh on the 27th., and dissipitated fast. The moisture content of the peninsula has been "sucked" away from the land, and the resultant satellite image today (29th.), shows absolutely clear skies over the entire region. Hence, what else but dry weather ?
I maintain, that the dry spell will last in the southern regions of India till about the 4th. of November. Around the 4th./5th., an easterly wave can bring some rainshowers to TN and coastal AP. No organised sysytem is seen forming till the first week of November in the bay.
In fact, a stationary ridge over the Arabian Sea and west coast of India will result in clear skies and slightly "warmish" days over the west/nortwest India and central /southern Pakistan.
Night temperatures have not dipped much over the sub-continent since my last write-up. Only the extreme north region, Ladakh, has seen a fall in the minimum temperatures, with Leh dropping to -5c.

Saturday, October 25, 2008

Continuing from the previous blog, the projected low in the bay has formed, intensified into a depression, and now, on Saturday evening, lies at 17N and 87E, 420 kms east south-east of Vizag. Susequently, this is expected to intensify more, and move in a north easterly direction. It should gain and become a cyclone within the next 36 hrs.
As a result of the strengthening , much of the moisture and rain clouds in the bay and in the southern peninsula today, will gradually get pulled towards the system. Resultantly, rains will decrease from the coastal regions and interiors of TN in the next 24hrs., and from coastal and interior AP after 36hrs.
Much rain, would now gain and concentrate in the Orissa, W.Bengal regions in the next few days.The system, cyclone "Abe" if named (Ashokbhai corrects me and informs the name will be "Rashmi"), would strike the WB/Banladesh coast around 28th.
Thus, I see a respite from rains for TN and AP from 26th./27th. The lull in the rains may last till the 4th. of November, when the effect of the system will wear off, and allow the easterly waves from the bay to bring back rain bearing clouds.
The bay depression is pulling in all the moisture from the weak low in the south Arabian Sea as well. The current rains in the southern peninsula is a result of the rain clouds being dragged across the land towards the east. Hence, this system in the western sea is expected to fizzle out soon.

Remarkably low temperature ( for this time of October),of 11.6c was recorded at Pune today, 25th.October, 18c is normal. Several stations in Maharashtra had 12c (Nasik and Ahmednagar).

In the extreme north, winter has started setting in the Kashmir/ HP regions. In HP, first snowfall has been recorded in the Rohtang Pass, and all the higher reaches. Kalpa and Keylong have recorded 0c as their lowest temperatures this season. In Kashmir, the low in Srinagar is now 4c, and -1c in Leh during the last 2 nights.
Next blog update of the cyclone and winter progress will be on 29th.

Monday, October 20, 2008

Starting from the Arabian Sea, the much monitored low there has concentrated into a depression. It now lies over the western Arabian Sea, almost skirting the Oman/Yemen coast and the coast of Somalia. At this postion, it is not going to affect the shores of the sub-continent as the movement of the system will be north-west, on deepening further.

I now wait for the forecasted low in the bay. It is expected to form around the 24th. off the coastal regions of A.P. Like I mentioned, its direction and intensification will be dependend on the WD, which will travel across extreme north of the sub continent around the 22nd. In all likeleyhood, within this scenario, the system will move northwards. I would not forecast the future intensification and actual direction of this system now.

As a result, the rainfall pattern and intensity for the southern peninsula will continue to remain as it is, till at least the bay low surfaces. But for the next 1 week, the "normal" north-east monsoon rains will continue, in the existing pattern, as the trough line embedded in the ITCZ, running from the depression, thru a low over Sri Lanka southwards, thus remaining just below the tip of India. Todays IMD streamline shows this clearly.

With the moving away of last week's WD, the night temperatures have started falling in the northern plains. Across the border, Islamabad night temperature fell to 12c, and in India, the Punjab towns saw 15c-16c (including Delhi). The IMD map shows a large area around north/central India in the 16s.But as the fresh WD approaches, these night temperatures may rise again from the 21st.

Due to strong inland easterlies along the west coast of India, the days have been abnormally hot since the last 2/3 days. Most of the coastal towns of Maharashtra have touched 37c, almost 4-6c above normal.
Mumbai too is hot at 36.6c being recorded at Colaba, and 37c at S'Cruz. during the last few days . The heat has been "stiffling" for the Mumbaites, as it is almost touching the all time high for October, at 38c, for, Colaba, and Santa Cruz. The Mumbai heat is expected to lessen from Wednessday,22nd., as with the WD approaching, the easterlies should change to north-westerlies.

Thursday, October 16, 2008

All on schedule! The south -west monsoon has given way to the north-east monsoon on the 14th. of October. As yet no organised system is seen in the bay, so, as mentioned, the rains will not be widespread in the south. The ICTZ having moved south, to almost 5N, is cause of the belt of rain clouds seen in satellite images on the southern tip of India and below.

But a low is forecasted in the bay during the week 21-28 October. Its intensification needs to be observed, though a few models have projected a cyclone in the bay by the 24th. I would wait for the advancing W.D., now a couple of days away, and then determine the bay system's movement.

The anticipitated low in the Arabian Sea has formed, and is now at 5N. Its movement is projected towards Oman, on intensification, but I would not rush into any forecasting now !

Meanwhile, a fairly active W.D. has whitewashed the upper hills of Kashmir with the first snow, and the plains of north India with winter rains. A sharp fall now in night temperatures for the north from 17th.

next update on 20th.

Sunday, October 12, 2008

Continuing from the last blog, the 200hpa westerly jet streams have slid further south, almost to 20N , and the sea level winds have completed their reversal, and the south-west monsoon has moved away from all regions of the country, except the southern states of Karnatak, A.P.,T.N., and Kerala. But the streamline map shows the entire southern region to be ready for the simultaneous "transition" of the south-west monsoon to the north-east monoon in couple of days.

Initially, the rains in T.N. not be very widespread in the absence of an organised system. But the 200hpa jet stream will bring the rain clouds inland as Easterly waves, in "immature formations", will push into the coastal areas of T.N. and south A.P.

Meanwhile, all international models show the formation of a low in the south Arabian Sea around the 16th. As mentioned, the heating up of the Maharashtra/ Gujarat and central peninsula regions can dominate the course of the low. Map from IMD shows the north-west regions of India, and adjoining Pakistan, heating up to temperatures above 39c. The heat is expected to cover the entire Gujarat/ Maharastra regions.

The low is projected to intensify, and move north in the subsequent days after 16th. Its movement will be watched after it forms.
Next blog will be updated on 16th. October.

Wednesday, October 08, 2008

With the 200 hpa westerly jet stream gradually pushing its way south, now having come down to 26N, the south-west monsoon has to give way and recede further down south.
As per my last blog, the winds and the jet stream patterns, and the atmospheric conditions, show, and, as per my assumptions, confirm with the complete widhrawal of the monsoon from all regions north of 20N.
The last of the stray isolated thundershowers will pop up in Maharashtra on the 8th. ,and, I feel, the monsoon should be bidding farewell to Maharashtra, Goa, North Karnatak and A.P. from the 9th.
By next week, the reversal of the south-west winds would be complete in the peninsula area, and the westerly jet stream should slide to the regions below 15N. Hence, it would be safe to predict the North-East Monsoon current to be picking up and rain bearing systems to start forming for the commencement of the reverse monsoon thereafter, say around 14th./15th. of October.
For the north-east monsoon systems to form, the influence from the equator region decreases, and the formation of a system in the bay directly depends on the strenght of the north-east winds, and the high pressure in the north China region, which is the main "power house".

The northern regions of the sub continent, are now getting some showers/winter rains due to a fairly active W.D. crossing the belt along N.Pakistan/H.P./Kashmir regions. Higher reaches in Ladakh had snowfall today. A sharp drop in night temperatures in the northern regions is expected once the skies clear on the passing of the W.D.

Some meteorologists and a few forecast models had foreseen the formation of a cyclone in the Arabian Sea by the 2nd. week of October. I do not see any signs of a cyclone forming off the west coast of India in the next 15 days at least. I limit myself to 15 days now, as the formation of a cyclone in this area is directly related to the "October heat" in the region. So, a lot depends on how much the land would heat up in the first 2 weeks of October.

Saturday, October 04, 2008

With the wind pattern getting more "un-monsoon" like over the sub continent, the monsoon is now sliding southwards. The winds shows a ridge in the Arabian Sea, and south -west monsoon current showing signs of dis-organisation.
To put the final stamp on the widhrawal, a W.D is forecasted by the IMD (also seen in the streamline), by the 6th. A W.D. is a typically winter system, and will push the monsoon trough down south.
In the meantime, a late partial re-strengthening of the Easterly 200hpa jet streams over the 20N region, (see map) has produced, the predicted rains, in Maharashtra, Gujarat and south M.P. regions.There were thundershowers in parts of Saurashtra, Konkan, Marathwada, south Maharashtra and south M.P. on the 3rd. and 4th. of October. Mumbai had thundershowers on the 4th.

These rains are expected to cease in Gujarat and the monsoon expected to move away from the areas north of Gujarat from the 6th.

However, Konkan, Ghat stations (Lonavala & M'shwar), and Marathwada can recieve some thunder showers for another 3/4 days, maybe upto Tuesday,7th. Heavy rain at a few places in the Ghats can be expected in this period.

Subsequently, with the W.D. seen to dominate the northern areas in a couple of days, the weak easterly jet streams can change directions, and indicate a monsoon widhrawal from Maharashtra and central India from the 7th.
Next blog update 8th. October.

Wednesday, October 01, 2008

Come October, and another settled and dry day all over and with the last of a weak Monsoon low fading, and the from satellite imagery showing cloudings sparsely near the India-Nepal border.

The streamline of the first day of October clearly indicates the almost total reversal of the winds in the sub continent, and, importantanly, in the Arabian Sea. The dry air penetrating over the peninsula has cleared the skies over the entire region, and resulted in a drop in the minimum temperatures over the central regions of maharashtra and M.P. (Pune at 16c and Aurangabad/Nasik at 18c ).

An over view of South Asia ( from "Thailand Met Dept" map), shows the ITCZ to have shifted to 22N over India, and running southwards towards the northern bay area, and then into the mid regions of Thailand. This is now expected to recede southwards fast, and move below the southern tip of India in about 15 days. That will hearld the total reversal of winds in the Indian region, and the onset of the "reverse" monsoon.

But, for the "reverse monsoon, we need a sysytem in the bay !
Another 5 days ahead, is another predicted low in the bay, a follow through from Tropical Storm Mekkhala, which has landed in Vietnam as of Tuesday. Numerical forecasts have been showing only a weak reflection of a low, owing at least partly to the moisture lacking northerly winds .

A weak, late-season spell of monsoon rains is forecast the coming weekend over peninsular India. This would favor local rain westward from interior Maharashtra with scattered thunderstorms elsewhere in north Karnatak nad south M.P.
Hence, the actual widthdrawal, below Gujarat, may be delayed by the IMD till this spell of rain fades away.
I shall put up my next update on 4th. October.

It is now expected that the night temperatures will start dropping in the northern states, Rajasthan, M.P. Gujarat and Maharashtra in the next week. But, the days are expected to remain warm all over this region for the next 15 days at least.

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