Wednesday, September 24, 2008

In the last blog, I mentioned that the monsoon was receding, but we had to observe the bay low which was forecasted for this week, before the rainy season restarts its reversing.

Now, there is big drying up of the Subcontinent, a sign of the reversal of the SW Monsoon as it withdraws.

A feeble low has formed in the North Bay of Bengal once again. It might just precipitate fairly widespread rainfall West Bengal, Sikkim and coastal Orissa only, and not take the path of the last depression.. It clearly lacks intensity to drive any further than that. Thus, as seen in the IMD streamline, the seasonal anti-cyclone (high pressure area with dry weather) is advancing in from extreme west Rajasthan.

Now, what about next week? No forecasts have been made about any fresh low in the bay now, but we have to watch the typhoon Hagupit, a Category-3 storm raging currently in the Northwest Pacific and heading towards the south-east China coast. Also, next in line, perhaps, will be a tropical wave centered in the area of Yap Islands as of Tuesday. This wave could become the next tropical depression as its drifts west-northwest over the southern Philippine Sea.

But all this activity in the Pacific, may be a booster to the North-East monsoon setting. Later in about 100/12 days hence, the leftovers of Hagupit could reform as a well-marked monsoon low near the head of the Bay.

This should initiate the onset of the North-East monsoon around mid-October. But before this, the southwest monsoon should have withdrawn completely , and the winds should change, which is indicative in today's map above. September 30 is the normal date for this to happen, but, due to the initial hiccup in its widhrawal, is behind schedule at least as of now.

It had been forecasted by some models and forecasters in the last week, of a MJO reviving, and likely increase of rain in the southern peneinsula. Now, as of this week, MJO forecasters see a depleting MJO causing a dry spell in the southern region of India. However, I feel, at this time of the year, specially during the "changing season" period, the effects of an MJO over the sub continent is minimal, due to stronger seasonal changes.

Almost dry weather in all of the sub continent (barring Bengal, Sikkim and some isolated rain in the north-east), till next week. However, "local" thunderstorms , though scattered, can be expected in Maharashtra, during the next 5/6 days. That is during the receding of the monsoon.

Saturday, September 20, 2008

The inter action of the low(remant of the deep depression) with the W.D. has caused heavy rain and snow in H.P.The rains and snow stared fromFriday,19th.
Heavy rain in most parts of the state and early snowfall in higher reaches of Kinnaur and Lahaul-Spiti have disrupted normal life in the state.
There are reports of snowfall in the higher reaches of tribal districts and Chitkul. Most parts of the state have been lashed by heavy rain. The monsoon has been very vigorous that triggered landslides and caused uprooting of trees.
In Shimla, there has been 111.58 mm rainfall since yesterday, causing landslides and disruption in vehicular movement. Trees have been uprooted at several places, including Khalini Chowk, and many of the link roads blocked due to landslides.
There has been 29 mm rainfall at Sundernagar, 30 mm at Bhuntar, 75 mm at Kalpa, 25 mm at Mandi, 79 mm at Solan, 45 mm at Kotkhai, 62 mm at Renuka, 97 mm at Rajgarh, 152.7 mm at Arki, 44.3 mm at Kasauli, 31.4 mm at Nahan and 48 mm at Dharampur.
Hundreds of vehicles were stranded on both sides of the 13,050 ft high Rohtang Pass, the gateway to Lahaul-Spiti valley.
Inclement weather conditions which worsened since Friday, caused hundreds of persons to spend the night in their buses and other vehicles due to fresh snowfall on Friday afternoon at both sides of the Rohtang Pass.
Leh, in Ladakh, also recieved its initial snowfall of this season on the 19th.
Punjab, too, had very heavy rain. The rains may not benefit the crops now, as they are not needed.
Also Gujarat, has had some record rains, with Dhandhuka, recieving a massive 500mms. in the 24 hrs. ended Thursday. Several places in Saurashtra recieved between 250-450mms in 24 hrs.

The "flood belt" is now spreading, and has covered Gujarat, Nasik and Nanded towns in Maharashtra, and Orissa in the east.
It seems , now , that the rains will drastically taper off in the flood affected states.
North will be much drier, and Maharashtra and Gujarat too will get some relief.
But, the IMD forecasted low in the bay next week is to be watched, before bidding farewell to the monsoons !

Tuesday, September 16, 2008

The much anticipated low in the bay has formed, and as discussed , intensified into a depression as on the morning of the 16th, and further into a deep depression by the same evening. Now that translate into very heavy rains, upto 250mms, in Orissa and parts of Chattisgarh, during the next 2 days. Paradeep in Orissa has already recorded 16cms. and several other places between 9-11cms. today.
The D.D. is expected to cross the Orissa coast by the night of the 16th., its centre was just 50 kms from the coast as on 17.30 IST.and move westwards towards M.P.
Meanwhile, the Upper Air Circulation over Gujarat since Sunday, is still persisting over the region. As a result, very heavy rains hs been recorded over several cities in Gujarat and Konkan. Very heavy rainfall of 20cms was recorded at Junagadh in Saurashtra region. Some stations in Saurashtra have had almost 250mm-300mm in the last 48hrs.
Now, the monsoon still may not relent. As mentioned earlier, the much delayed West Pacific Typhoon activity may yet throw up another system in the bay. ECMWF has forecasted another low in the region around the 24th. May not intensify much, but will certainly prolong the rainy spell over the heartland a little longer.

Meanwhile, the highly active bay, in the last 2 weeks, has concentrated on the formation of systems around the central bay area, which subsequently cross the Indian coast on the Orissa shoreline. This has resulted in most of the rain pouring down north of Karnataka and caused a slowing down of the precipitation over the southern peninsula.
Extreme northern regions of the country too, have had no rainfall due to the absence of W.D.s. No W.D. can be expected now, for a week, as back to back lows are crossing across the central regions.
Since the systems from the bay are moving along the monsoon trough axis, that is across central India, the regions above and below the "path" can remain comparitvely "rain free."

Saturday, September 13, 2008

Point by Point follow-up from the write up of 9th.Sept.

1. The low from the bay crossed the A.P. coast on the 11th. and moved along the axis of the monsoon trough, and subsequently produced heavy rain along its path in Maharashtra,Gujarat and A.P. Then, on the 12th., it merged with the low over Maharashtra, and on the 13th. morning was over central Maharashtra. The happenings are a day or two later than predicted.

Temperatures in north Maharashtra came down drastically due to this. It was 23c(-7) at Aurangabad and 24c at Nasik in the day on 13th..(see map).

2.The system now seems to be moving north-west. Expected over Gujarat coast by 14th. Heavy rains have already commenced over Gujarat.

3. Now, the map also shows the heat searing on the sindh coast at 42c. Since the last 2 days its been at 42c. This may "invite" the system, at whatever strenght, to proceed towards the "heat low" created over the sindh coast.

As hoped, the system has travelled thru the deficit regions of Marathwada. The deficit in these regions is now getting wiped out, and the rain total is fast reaching the normal level.

The next forecasted low is expected in the bay by the 15th. This , is predicted to become a depression, and cross the Indian east coast. This will surely drench the northern peninsula region, with the possibility of Maharashtra and M.P. getting a major share of the precipitation initially.

Well, surely, the withdrawal of the monsoon is now pushed back. Two back to back systems from the bay, in the fag end of the season, has reversed the withdrawal as the monsoon trough has suddenly become active again.

With Typhoon Sinlaku being followed by another Tropical Storm 16W in the west Pacific, possibily we could yet see another system in the bay around the 21st. This "last moment" bursts of storms in the Pacific may prove to be a bonus for the monsoon rains. Specially when in the 1st. week of September, it almost seemed the monsoon was on its way out.

Tuesday, September 09, 2008

"The weather has changed"--in effect the "sort of " receding monsoon symptoms have stopped at Rajasthan. The winds have re-grouped, as mentioned in the previous blog, to form a low in the bay. The widhdrawal phase, fortunately has been postponed.
The low in the bay, off the Orissa coast, as on the evening of 9th., supplimented with a "low"circulation over Maharashtra, has literally pulled the monsoon axis to the 22N level, and normal easterlies have resumed over the region north of the trough, that is over U.P., M.P. and nort-west India.
The bay low and the Maharashtra low have produced widespread rains over all of Maharashtra, south Gujarat regions north Karnataka and A.P.
Now, predictions show that: 1. The bay low will move inland and travel along the monsoon trough, till, say in one day,before it merges with the low over Mahrashtra. Result: Heavy rains all over Maharashtra, M.P., A.P. Karnataka, and south Gujarat on the 9th.,10th.
2. The system is expected to move north-west, and cross into the Arabian Sea and move towards the Sindh coast, before fizzling out. Result: Rains and strong winds off north Maharashtra /south Gujarat coast on the 11th. Good rains in south Gujarat and Saurashtra regions on the 10/11th.
3. Rains subsequently can move towards the sindh coast by the 11th. and decline as the system fizzles out there.
4. We may yet see the other depression forecast by the ECMRWF by the 15th of this month.
The current change may prove to be a boon for the deficit regions of Marathwada and the mid September rains will boost the water table in the dry regions of Gujarat.

Saturday, September 06, 2008

A fairly active W.D. has moved across northern subcontinent, and precipitated good rains in the region and snow on the mountains. In Pakistan, heavy rains in the north-east has occured, but the rains may be restricted to that region, as the W.D. moves away. Local fall in temperatures in the far north can be expected.
A steady drizzle brought down the temperature in Srinagar by several degrees, giving the residents the first feel of impending winter. an overall drop in day temperatures today, due to the W.D. is seen in the map from University of Cologne.
The normal temperature today was whopping 7°C less than the normal. The resort of Gulmarg, and other higher reaches had the first snowfall of this season. In H.P., heavy hailstorms lashed the hilly region.

This system has distanced itself from the southerly monsoon currents, but southwards, the monsoon south-westerlies are making a "final attempt" to re-group. A weak orderly south-west wind has re-formed along the central and western areas of India, as seen in the IMD 925hpa map. Also, due to regrouping, overnite changes in model predictions are made.

-The IMD forecasts a low in the bay by the 7th. and some rain as a result along the regions west of the low crossing the east coast. On the crossing of the predicted low inland, the west coast, and ghat stations of M'shwar/Lonavala can get sudden heavy precipitation, around Tuesday/Wednessday (9th./10th.).

-This is enforced by COLA, which predicts, (most probably the same low), to cross into the Arabian Sea. Resultantly, a low vortex is forecasted off the coast of Karnatak/Maharashtra around the 9th. Result: Heavy rains along the coast and ghats on these days.

-Meanwhile, the ECMRWF also forecasts a depression crossing the A.P. coast around the 15th. If true to forecast, much more rain can be expected by the 15th./16th. in the states directly in the path of the depresiion. ( could be north westwards from the A.P. coast, as indicated by the forecast model).

Again, if true to forecast, my estimate of the monsoon widhrawal date should be extended ( stands much to the benefit of the entire peninsula region).

If the above systems do not materialise, or , if the recent regrouping is weak and temporary (we hope not), the ensuing northerly dipping trough (W.D.), is going to push the monsoon axis southwards really fast.

Wednesday, September 03, 2008

The monsoon seems determined to move out early, at least it has started from the Rajasthan region after leaving the sindh areas. The IMD 925hp. streamlines show distinct north-westerlies over the Rajasthan area and a "westerly disturbance" trough over Pakistan. Indications of clear "drying up" of the region is seen in the IMD humidity map showing a reduction in the humidity over Rajasthan. The state has not had any rain for the last 7 days now, supporting a widhrawal.

A line of wind discontinuity has formed over central India, (seen in the map above) caused by the north-westerly/south westerly winds, which may bring down the monsoon axis faster.

As anticipated, the day temperatures have started rising in Rajasthan/Gujarat, and I expect them to rise by the 2nd. week to 40c levels. ities in Sindh may see the days go upto 42c !

Northern Gulf regions have seen a sudden spurt in day temperatures, with Mutrba in Kuwait at 51c, and Dubai regions around 40/41c. Expect the heat to wane away after a week, with the westerly winds expected to gain by then.