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Vanakkam! All is quiet on the North-East monsoon front over land this Wednesday morning but thunderstorms lurk in the seas around Sri Lanka as well as in spots off the South Andhra Pradesh coast. Chennai city is expected to see a partly cloudy day followed by a few clouds in the evening/night with hardly any chance for precipitation.
A few billowing clouds were seen over the Adyar River this morning, apparently having been pushed inland from off the South Andhra Pradesh coast by the northerly to north-easterly winds. These could be potential weather-causing clouds in as much as there is a the pink tint at their base.
As the old saying goes: red sky in morning, sailor's warning. A red sunrise can mean that a high-pressure system (good weather) has already passed, thus indicating that a storm system (low pressure) may be moving to the east. A morning sky that is a deep, fiery red can indicate that there is high water content in the atmosphere. What the pink tint in the cloud means for Chennai needs to be observed since dry conditions under partly cloudy skies is the call from international models.
The skies over Besant Nagar's Broker Bridge were clear this morning.
The skies over Besant Nagar's Broker Bridge were clear this morning.
Other areas
Puducherry might fare better than Chennai with a 40 per cent chance of showers into the night. Salem is likely to see a dry day today, while it will be partly cloudy in Coimbatore and Madurai. The weather will be fair in Tiruchirappalli and cloudy in Thoothukudi.
The North-East monsoon seems to be on the way out but international models suspect that it might sign off with a customary flourish around Sri Lanka and the adjoining southern parts of Tamil Nadu over the next week or so.
Positive IOD weakens, but only just
Meanwhile, the Australian Bureau of Meteorology has assessed that the positive phase of the Indian Ocean Dipole (positive IOD, representing a warming bias to the western basin of the ocean relative to the East) has weakened a tad while continuing its run into the second week of December. It has underwritten a successful South-West and North-East monsoon this year and also scripted the saga of a record-matching eight cyclones that marched across the Arabian Sea and the Bay of Bengal waters during this period.
The Australian agency said that the IOD values have gradually weakened since their peak of +2.1 degrees Celsius mid-October. However, the latest weekly value of +0.9 degrees Celsius is still well above the positive IOD threshold value of +0.4 degrees Celsius. Warmer-than-average waters persist near the Horn of Africa (Somalia, and adjoining South-West Arabian Sea) but the cooler-than-average waters in the eastern Indian Ocean have now returned to near-average sea surface temperatures.
El Nino on the mend?
Most international climate models surveyed by the Bureau indicate the positive IOD will dissipate by the mid-Australian summer (December to February) as the monsoon moves into the southern hemisphere. Typically, a positive IOD brings below-average rainfall to southern and central Australia with warmer days for the southern two-thirds of the country.
Positive IOD events are often associated with a more severe fire season for South-East Australia. The recent flooding in East Africa is also typical of a positive IOD event. In the tropical Pacific Ocean, neutral conditions prevail (neither El Nino or La Nina). However, abnormally warm sea surface temperatures in the western tropical Pacific (unlike in the eastern tropical Pacific that sets up EL Nino conditions) may be contributing to some changes in weather patterns over the region.
When the tropical western Pacific Ocean (unlike the eastern basin) warms up beyond a threshold on a sustained basis, it can set up La Nina, the alter-ego of El Nino, considered beneficial to the next South-West monsoon in India. But international climate models forecast neutral conditions to prevail for early 2020. Where El Nino or La Nina are absent, the ensuing tropical Pacific conditions have a reduced effect on global climate, and other influences are more likely to dominate.
Rain, snow in North India
Meanwhile, back home, the weather is busying up over North India with western disturbances arriving in batches and bringing in moisture and warmth to modulate the winter weather. These elongated low-pressure bands are secondary or tertiary branches of the jet streams that are synonymous with winter storms in Europe and America. They originate from as far North-West as the Mediterranean-Caspian Sea, cross Central Asia, West Asia, Iraq, Iran, Afghanistan and Pakistan to enter North-West India.
When they are intense or with depth with a limb dropping down to the Arabian Sea, they carry incremental moisture and induce the formation of secondary circulations over North-West India, leading to snowfall in the hills and thundershowers in the plains.
Once the western disturbance passes further East and out of the country, colder Arctic air fills and sets up biting cold till such time as the next warm western disturbance shows up. In fact, the India Meteorological Department (IMD) has located an incoming western disturbance this (Wednesday) morning over over Afghanistan and its neighbourhood. Under its influence, an induced cyclonic circulation is likely to form over South-West Rajasthan and adjoining Pakistan by tomorrow (Thursday).
Rainfall for North and Central India
This is expected to set up weather of maximum intensity with widespread rain/snow with isolated heavy falls over Jammu & Kashmir, Himachal Pradesh and Uttarakhand on Thursday and Friday. Light to moderate scattered/fairly widespread rainfall is likely over Punjab, Haryana, Chandigarh, Delhi, West Uttar Pradesh, North Rajasthan and North Madhya Pradesh on Thursday and Friday.
Isolated heavy rainfall is likely to occur over North Punjab on these days and over North Haryana on Saturday. Thunderstorms/hailstorms accompanied by lightning are forecast at isolated places over Jammu & Kashmir and Himachal Pradesh from today to Saturday; over Uttarakhand, Punjab, Haryana, Chandigarh and Delhi and North-West Uttar Pradesh on Thursday and Friday.
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