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A prevailing cyclonic circulation over the Malacca Strait (between Malaysia and Indonesia) has locked itself into position over North Sumatra (Indonesia), and will now move West-North-West into the South Andaman Sea to set up the anticipated low-pressure area there in next two days.

The India Meteorological Department (IMD) said on Wednesday that the low-pressure area would concentrate into a depression during the subsequent two days. It could intensify further (likely to a deep depression) and move North-North-West (facing India’s coast) during May 1-3 and subsequently North-North-East (away from India’s coast) towards the Myanmar-Bangladesh coasts.

MJO wave in

Arrival of a strong pulse of the Madden-Julian Oscillation (MJO) wave into the East Indian Ocean and adjoining South Bay of Bengal has prepared the ground for this development. The MJO wave moves periodically in the higher levels of the atmosphere with its paraphernalia of cloud, moisture and precipitation and helps with monsoon onsets and storm development in the region under its footprint.

Squally winds with speeds reaching 40-50 km/hr gusting to 60 km/hr are forecast over the South Andaman Sea on May 1 (Friday), the Nicobar Islands, and the adjoining South-East Bay of Bengal. Wind speeds may increase to 45-55 km/hr gusting to 65 km/hr on Saturday, and to 50-60 km/hr gusting to 70 km/hr over South-East Bay and adjoining South Andaman Sea on Sunday.

Pre-monsoon thunderstorms

The 24 hours ending on Wednesday morning saw heavy to very heavy rainfall at isolated places over Kerala while it was heavy at isolated places over Rayalaseema, South Interior Karnataka and Tamil Nadu. Hailstorm was reported at isolated places over West Madhya Pradesh and Telangana while a thundersquall (with wind speeds exceeding 65 km/hr, almost cyclonic strength) ambushed Vidarbha.

Pre-monsoon thunderstorms dumped moderate to heavy rainfall accompanied by lightning and high winds also over parts of East and North-East India during this period. Among the main rainfall events recorded were (in cm) Bengaluru-9; Thiruvananthapuram, Cherrapunji and Agartala-5 each; Anantapur, Coimbatore, Dhubri and Kailashahar-4 each; Arogyavaram, Tiruttani, Vellore, Kochi, Periakulam, Pasighat and Goalpara-3 each.

Kerala will continue to witness scattered to fairly widespread rain/thundershowers during the next two days. An identical forecast is valid for Maharashtra, Goa and north Interior Karnataka from Wednesday to Friday. Isolated thunderstorms, lightning, gusty winds (30-40 km/hr) are also likely over these regions during this period. Meanwhile, an approaching western disturbance would trigger isolated to scattered rain or thundershowers over the hills of North-West India (Jammu & Kashmir, Himachal Pradesh and Uttarakhand) and the plains of Punjab, Haryana, Chandigarh and Delhi from Thursday before peaking in the subsequent two days.

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