Extremely Heavy Rain Threat in North Bihar as Cyclone Arnab Weakens

Key Takeaways:

• Extremely Heavy Rain Threat: North Bihar faces the possibility of isolated extremely heavy rainfall on October 30 as Cyclone Arnab's remnant moves north-northeastwards.
• Very Heavy Rain Warning: Eastern Uttar Pradesh, Sub-Himalayan West Bengal and Sikkim may experience isolated very heavy rainfall, while Jharkhand could receive heavy showers.
• Cyclone Arnab Weakens: The system has weakened into a well-marked low-pressure area over northern Chhattisgarh but continues to support significant inland rainfall.
• Gradual Weekend Improvement: Rainfall activity is expected to decrease across Bihar, Jharkhand and Gangetic West Bengal from October 31, with further improvement likely by November 1.
• Forecast Validity: October 30 – November 1, 2026

North Bihar faces a significant rainfall threat on October 30, with chances of isolated extremely heavy falls as the remnants of Cyclone Arnab move north-northeastwards. Eastern Uttar Pradesh also carries a very heavy rain warning, while Sub-Himalayan West Bengal and Sikkim face locally intense rainfall. The main concern is now inland rain rather than coastal cyclone winds, with potential disruption to harvesting, road travel and drainage in areas receiving repeated downpours.

At 5:30 AM IST on Friday, Arnab’s remnant was seen as a well-marked low-pressure area over northern Chhattisgarh and neighbouring areas. The system is expected to weaken further while continuing north-northeastwards. Although its circulation is much weaker than during the coastal cyclone phase, it remains capable of transporting moisture and organising rain-bearing clouds. Convergence around the remnant, together with the wider atmospheric pattern, can sustain substantial rainfall well away from its centre.

For October 30, we expect the highest rainfall category over northern Bihar. Eastern Uttar Pradesh has a very heavy rain warning, while Jharkhand may receive isolated heavy rain. Farther east, Sub-Himalayan West Bengal and Sikkim also face isolated very heavy rainfall. These are forecasts of localised intensity, not an indication that every district will experience the same conditions. City-specific timing and the placement of persistent rain bands require district forecasts and short-duration nowcasts.

Rainfall coverage is expected to decrease over Bihar, Jharkhand and Gangetic West Bengal from October 31, although Bihar retains a thunderstorm and gusty wind forecast on Saturday. Sub-Himalayan West Bengal and Sikkim may continue receiving rain at many places through October 31 before activity becomes less widespread on November 1. The overall outlook, therefore, suggests gradual improvement over the weekend, with the most intense phase concentrated on Friday.

Farmers should move harvested grain under cover and avoid spraying immediately before rain. Drivers should not cross flowing water or enter inundated underpasses. Residents near small streams and poorly drained settlements should monitor local instructions. Heavy rainfall can cause rapid runoff, but river flooding also depends on upstream rainfall, existing water levels and catchment conditions. Improving weather will not immediately remove hazards from saturated ground, damaged roads or swollen streams.