Friday, October 09, 2009

Stray forecast says Bay buzz may gain strength from Saturday

An India Meteorological Department (IMD) update on Thursday said that the rain-driving upper air cyclonic circulation over north Bihar and neighbourhood persisted from overnight.

A trough from this system ran down to south Bay of Bengal, the IMD added.

According to the National Centre for Medium Range weather Forecasting (NCMMRWF), the system is expected to move towards sub-Himalayan West Bengal during next 24 hours before moving further east to over Assam.


An NCMRWF outlook cited model predictions suggesting the formation of a cyclonic circulation over east-central Bay of Bengal and adjoining area around October 10. The system is likely to intensify, the forecast added.

The IMD has forecast fairly widespread rainfall with isolated heavy to very heavy falls over sub-Himalayan West Bengal and Sikkim during the next 24 hours and over the north-eastern States during the next two days.

Weather is likely to remain mainly dry over west and central India and plains of north-west India.

Satellite images on Thursday showed convective clouds over parts of south-east Bay of Bengal, south Andaman Sea, sub-Himalayan West Bengal, Sikkim and the north-eastern States.

A warning valid for the next two days said that heavy to very heavy rainfall is likely at a few places over the north-eastern States.

Isolated heavy to very heavy rainfall has been forecast over sub-Himalayan West Bengal and Sikkim during the next 24 hours.

A short-term forecast for three days ending October 13 said that scattered rainfall activity is continue over the north-eastern States and extreme south peninsular India.

The IMD expected the monsoon is likely to resume withdrawal from the remaining parts of northwest India and some parts of east and central India during this period.

As of now, the withdrawal line is stuck across the eastern fringes of northwest and central India.


Early forecasts from the European Centre for Medium-Range Forecasts (ECMWF) suggested deficit rains for northwest India during October-November-December. But normal rains from winter monsoon (northeast monsoon) are indicated for the south peninsula.

November-December-January may set off a sustained trend for normal to excess (in isolated cases) winter rains for the north-west even as benign weather conditions are indicated for the peninsula. West-central Maharashtra, Vidarbha and Orissa are about the only exception.

December-January-February would turn out to be even better for the north-west as an extension of what is likely to be exceptionally good showers over the Middle-East, Afghanistan and Pakistan.

North coastal Andhra Pradesh, Orissa and Gangetic West Bengal are also seen gaining in tandem.

January-February-March is forecast to be slightly bad for the peninsula but the reasonably good run over the northwest is forecast to continue.


In its end-of-season report for the 2009 monsoon, the IMD said that for the country as a whole, the rainfall was 77 per cent of its long period average (LPA).

Seasonal rainfall was 64 per cent of its LPA over north-west India; 80 per cent over central India; 96 per cent over the south peninsula and 73 per cent of its LPA over the north-east.

Monthly rainfall was 53 per cent of LPA in June; 96 per cent in July; 73 per cent in August; and 79 per cent in September.

Like the last two years, there has been a delay in the withdrawal of monsoon due to rainfall over north India associated with the mid-latitude westerly activities (western disturbances).

The withdrawal from west Rajasthan started only on September 25, amounting to a delay of more than three weeks. The normal date of withdrawal from extreme western parts of Rajasthan is September 1.

Subsequently, the system has withdrawn from most parts of the north-western states and from the northern parts of Gujarat by September 28, the IMD said.


The operational forecast for monsoon onset over Kerala was correct, which is the fifth consecutive correct forecast for this event since issuing this forecast started in 2005.

The long range forecast for rainfall over the country as a whole and over four homogeneous regions except south peninsula have not been accurate, the IMD said.

The forecast for August rainfall over the country as a whole also was not accurate. All these amounted to a case of overestimation of the eventual rains that fell on ground.

However, the forecast for seasonal rainfall over south peninsula and that for July rainfall over the country as a whole were more or less on target.

Maverick monsoon? -- The MJO

A little-known weather phenomenon may hold the key to the sudden surge in showers this festive season and also the extended stay of the monsoon.

Experts blame the erratic behaviour of the monsoon on the Madden-Julian Oscillation (MJO), a fluctuation in the atmospheric pressure over the equatorial Indian Ocean and western Pacific Ocean.

MJO is named after the American atmospheric scientists Roland Madden and Paul Julian, who first documented the phenomenon in 1971.

"The mechanism and cause of MJO is still being studied. It's the most likely cause for the surge in September rainfall in the city and the rest of the state," said an independent weather analyst.

"The phenomenon is also believed to be the principal trigger for the monsoon anomaly on a national scale - flood in some states and drought in others," said Gokul Chandra Debnath, the director of Regional Meteorological Centre, Alipore.

MJO, which has no regular cycle of occurrence, comes in the form of alternating cyclonic and anticyclonic formations, which move eastward along the Equator. Originating in the Indian Ocean near East Africa and moving towards the Pacific, the MJO usually lasts between 30 and 60 days.

"It can influence rainfall by adding moisture to the system during its wet or cyclonic phase and reducing convection during its dry or anticyclonic phase," said an official from the India Meteorological Department in Pune.

Weather analysts said MJO hit the Indian Ocean during a cyclonic phase around August 24, affecting monsoon activities over the Bay of Bengal and resulting in heavy showers throughout September as well as the extended stay of rains.

According to meteorologists, the departure of the monsoon from the state - scheduled for October 7-8 - is likely to be delayed by a week

This is the latest MJO forecast for next 30 days.

And MJO suggest bad news for the entire NE monsoon.

Sand Dunes Reveal Unexpected Dryness During Heavy Monsoon

The windswept deserts of northern China might seem an odd destination for studying the heavy monsoon rains that routinely drench the more tropical regions of Southeast Asia.

But the sandy dunefields that mark the desert margin between greener pastures to the south and the Gobi Desert to the north are a rich source of information about past climates in Asia, says University of Wisconsin-Madison geographer Joseph Mason. Wetter periods allow vegetation to take root on and stabilize sand dunes. During dry spells, plants die off and the dunes are more active, constantly shifting as sand is blown away and replenished.

Such patterns of dune activity provide a history of the area's climate - if one can read them, Mason says. "When did those periods of stability or activity occur and from that, what can we infer about climate change?"

As reported in a new paper in the October issue of the journal Geology, Mason and colleagues mapped sand dune activity across northern China and found unexpectedly high levels of mobility and change 8,000 to 11,500 years ago, a time period generally thought to have a wetter climate. The result challenges existing ideas about the monsoon's regional influence and could impact future climate predictions.

Today, the dunes are at the edge of the monsoon region and the scientists expected to find close correlation between precipitation in the dunefields and the strength of the monsoon.

What they found instead was rather surprising. "They turn out to be almost completely out of phase," Mason says. "Where we find lots of active dunes turns out to be a time when the monsoon system is supposed to have been stronger in southern and central China."

Part of the explanation may lie in local patterns of atmospheric circulation. At the peak of the summer monsoon, central China experiences both heavy summer rainfall and strong upward airflow. That upward flow tends to be balanced out by more downward air motion - which suppresses precipitation - in areas north and west of the monsoon core.

Regional climate modeling data from the UW-Madison Center for Climatic Research, led by co-author and UW-Madison professor of atmospheric and oceanic sciences Zhengyu Liu, shows that this pattern may have been strengthened between 8,000 and 11,500 years ago. The models also show high summer temperatures at that time, which would have increased evaporation and further reduced the moisture that supports dune-stabilizing plants.

This pattern of climate change had been described for areas distant from the monsoon, like Central Asia around the Caspian and Aral Seas and in northern Mongolia. However, Mason says, "It hasn't really been recognized that this effect could be going on in northern China, which is where our study sites are. What it means is there's much more of a contrast in climate change across a fairly short distance."

The new findings relied on a technique called optically stimulated luminescence (OSL), which dates the last time the sand was exposed to sunlight. Radiocarbon dating methods are of limited use since sand typically contains little or no organic material. The OSL method identifies time periods when the sand was actively moving around, indicating little precipitation, and times when dunes were stable.

Mason's previous work in the area suggests that moisture and precipitation are the most significant factors in determining the activity of the Chinese dunes. The new results mean that common assumptions about the effects of future climate changes - including the increased monsoon rainfall predicted by many climatologists - may be incorrect.

"If monsoon rainfall increases in southern China over the next century, the logical assumption would be that these dunes would become more stable as more precipitation also reaches the dune fields and increases vegetation cover," Mason says. "That may not be true… The dunes can become active and the climate there can become drier even when the monsoon is getting stronger."

Even if future rainfall in northern China isn't reduced by changing air circulation patterns as it was in the past, rising temperatures will undoubtedly increase evaporation, he says, exacerbating the water shortages that already plague the area. An accompanying increase in sand dune activity would reduce available grazing land and worsen air quality.

"If it's drier you have less vegetation and the dunes are active. There will almost certainly be more dust produced, which is a major environmental hazard. Some of the dust from northern China actually reaches Korea, Japan and even the western U.S.," says Mason.

The paper is co-authored by colleagues in China, the Illinois State Geological Survey, and the University of Nebraska-Lincoln. Funding was provided by the National Science Foundation, the National Natural Science Foundation of China, the China National S&T Basic Work Program, and Nanjing University.

Expect normal NE monsoon: Met dept

Director General of Meteorology Ajit Tyagi on Thursday said the north-east monsoon in Tamil Nadu this year was likely to be normal.Talking to mediapersons after inaugurating the High Performance Computing System at the meteorological department office here, Tyagi said the north-east monsoon in Tamil Nadu this year was likely to be "normal or slightly above normal". Asked when the monsoon would set in, he said the likely date would be October 20, going by the average dates of monsoon for the past 100 years. "We expect some weather-related activities in the east coast from October 15 itself," he said. S R Ramanan, director, Regional Meteorological Centre, Chennai, said the monsoon had set in on November 2 in the past. Responding to a query on why temperatures are high even after the first week of October, Ramanan said: "If the sky is clear in the morning, then the day will be hotter. This need not be confused with global warming." He further said the temperature goes up due to three reasons - air pollution, urbanisation and global warming and this particular case could be attributed to the first two reasons. Ramanan said the south-west monsoon was normal by and large and only in certain districts there was a difference in the amount of rainfall.

Chennai - Clouds has gone high, it has become bit cold and humidity is going down.
Flooding and landslides in western Nepal has so far claimed 54 lives
40 killed as late rains spread disaster in Nepal ..
Late rains in north India seen conducive for wheat...
Kanyakumari Pictures ..
Chennai - Heavy showers in Vepery, Choolai, Purasaiwalkam and egmore zone.
RT @jishnuvv: After a log time, i saw rain clouds and thunder sound in chennai.
Chennai - First sign of NE monsoon... lots of thunder
RT @Balatweets: Chennai is anticipating the much much much awaited rain!!!! Will the thunder translate?
Chennai - Super Thunder storm over northern suburbs Chennai
Chennai - Good sea breeze from south-east... possibility of a Thunder shower is increasing.
Chennai - Getting cloudy with good LOW cloud formation... Temperature just touched a high of 35.1°C (12:54pm)
Chennai - Sky covered with 70% high cloud
Now Tamilnadu should wait for the NE monsoon. Chennai was bit cloudy in early morning, now 9:44am also its covered with high dead cloud.
Wow...! .. a clear looking INDIA after a long time.. signalling the END of SW monsoon ..