TRACK TO SOUTH
Initial signals from the US National Centres for Environmental Prediction (NCEP) show that the long-delayed pre-monsoon ‘low' may take shape during this period.
NCEP projections show that the system may get generated over south-central and adjoining southwest Bay of Bengal and track south-southwest to hit southern Sri Lanka first.
The weakened system is shown to take a northward course then and aim the Kerala coast for a second hit.
Forecast until May 19 shows the southwest coast and adjoining south interior peninsula slipping under rain cover of varying intensity.
It may be too early to call an onset of monsoon anytime soon, but all major weather models are indicating the arrival of a wet phase of the Madden-Julian Oscillation (MJO) wave during the course of the next two weeks.
An MJO wave travels periodically from the west to east (covering Indian Ocean to the Pacific) and has alternating ‘wet' and ‘dry' phases.
These waves have been known to trigger monsoon onset, formation of low-pressure areas and cyclones on the one hand, and intra-seasonal ‘droughts' and rain shutouts on the other.
All major models surveyed seem to unanimously agree that the MJO wave would peter out by May 18, bringing forth a ‘dry phase' of the MJO wave. However, according to the Earth System Research Lab (ESRL) of the US National Atmospheric and Oceanic Administration (NOAA), the wet phase of the incoming MJO wave would hold strong until May 24.
CONCENTRATED ACTION
The ESRL has indicated that concentrated action of the MJO wave would be on view on extreme south peninsula around May 17, the normal time for monsoon onset over the Andaman and Nicobar Islands.
The onset over these eastern islands, which is the first outpost for southwest monsoon in the territorial waters, is known to precede the onset over Kerala over the mainland by around two weeks.
Sea-surface temperatures (SSTs) in the Bay have been hovering in the high-30 deg Celsius for sometime now.
It was particularly high around the Andaman and Nicobar islands and just to the southeast of the Kerala coast on Monday.
Meanwhile, pre-monsoon activity continued unabated over large parts of the country even as a weather-setting western disturbance aimed to cross the international border and enter into northwest India on Monday.
A weather-setting trough lay parked west to east from northeast Madhya Pradesh to Assam, an India Meteorological Department (IMD) update said on Monday.
It cut across north Jharkhand, Gangetic West Bengal, north Bangladesh and Meghalaya with an embedded upper air cyclonic circulation over north east Madhya Pradesh.
A north-south trough ran down from northeast Madhya Pradesh to the Tamil Nadu coast across east Vidarbha, Andhra Pradesh, south interior Karnataka and Tamil Nadu with an embedded upper air circulation over Tamil Nadu.
The western disturbance over northeast Afghanistan and adjoining north Pakistan persisted with an induced upper air cyclonic circulation over central Pakistan. It is expected to impact the western Himalayan region with moderate strength.
Satellite imagery showed convective (thundershower-causing) clouds over parts of west Uttar Pradesh and adjoining east Uttar Pradesh and Uttarkhand and southwest Arabian Sea.
Low to medium clouds (partly clouded conditions) were seen over parts of southeast Bay of Bengal, northeast Andaman Sea and the remaining parts of the country except Punjab, Haryana, Rajasthan and Gujarat.
The IMD update warned of the possibility of isolated thunder squalls over Bihar, Jharkhand, West Bengal, Sikkim and the Northeastern States during next two days.
Isolated thunder squalls are likely to occur over peninsular India and Uttar Pradesh during next 24 hours while scattered to fairly widespread rain or thundershowers would occur over the Northeastern States.
Isolated dust storm or thunderstorms would occur over Punjab, Haryana, Delhi, Chandigarh and Uttar Pradesh during next 24 hours and again from Thursday. Isolated thunder squalls would also occur over these regions during this period.
As for rest of the country, isolated rain or thundershowers would occur over Maharashtra, Madhya Pradesh and Chhattisgarh during next 24 hours.
Scattered rain or thundershowers has been forecast over east India, peninsular India, Lakshadweep and the Andaman and Nicobar Islands.
No significant change is seen in maximum temperatures over parts of northwest, central, east and peninsular India during the next two days.
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