Monsoon Update 02 August 2026 — Deep Depression Was Chief Rainfall Driver Last 3 Days; Axis Now Sweeping Northeast; Bihar RED Alert 04 Aug; Bay of Bengal System Watch 07–11 Aug

The Deep Depression that made landfall over the Gujarat/Saurashtra coast on 30–31 July was the dominant rainfall driver across central India for the last three days — producing Extremely Heavy Rain over Gujarat, Vidarbha, and South Chhattisgarh and setting the context for the Valsad extreme event and the subsequent offshore trough re-activation. That system has now dissipated, and the VayuMet model (GFS IC 02 Aug 00 UTC) shows the monsoon axis resetting and sweeping decisively northeast. The next four days bring an orderly procession of heavy rainfall eastward: UP and Rajasthan on 03 Aug, Bihar peaking on 04 Aug, West Bengal erupting by 05 Aug. Looking further ahead, an exceptionally strong Bay of Bengal signal is developing for 07–11 August — the 200 hPa upper-level divergence pattern is among the most pronounced seen this season.

Mean Sea Level Pressure and anomaly vs 1981–2010 NCEP R2 LTM · GFS IC 02 Aug 2026 00 UTC · Left: 02–06 Aug · Right: 07–11 Aug

Trough Lifting North — Bay of Bengal Low Developing by Day 6–10

The Day 1–5 MSLP chart shows a residual low (~998–1000 hPa) over the Saurashtra coast — the decaying remnant of the Deep Depression — with the monsoon trough extending northeast across Rajasthan and the Gangetic plains. The negative MSLP anomaly of −4 to −6 hPa over northwest India and the foothills confirms the trough is still deeper than the long-term mean, sustaining active conditions. By Day 6–10, the picture changes markedly: the negative anomaly over northwest India relaxes toward neutral while a fresh negative anomaly consolidates over the Bay of Bengal and sub-Himalayan northeast. This is the MSLP signature of a new lower-tropospheric circulation organising over the northern Bay — the next system beginning to announce itself.

Cumulated Rainfall (mm) and anomaly vs 1991–2020 LTM · GFS IC 02 Aug 2026 00 UTC · Left: 02–06 Aug · Right: 07–11 Aug

Above-Normal Rainfall Belt Shifting Northeast — Bay Signal Dominant by Day 6–10

The Day 1–5 rainfall anomaly shows the above-normal belt concentrated over northwest India — Rajasthan, UP foothills, and the Himalayan arc — with anomalies of +60 to +100 mm. This is the trailing active period of the post-depression trough. Northeast India is independently heavy throughout. By Day 6–10, the above-normal signal retreats from the northwest and re-emerges with intensity over northeast India and the Bay of Bengal zone — consistent with a new system organising and directing moisture into the northeast quadrant. South India shows a persistent below-normal anomaly in both periods as the Arabian Sea Low-Level Jet (LLJ) continues to pump moisture northward rather than toward the Peninsula.

Mean 2 m Temperature (°C) and anomaly vs 1991–2020 LTM · GFS IC 02 Aug 2026 00 UTC · Left: 02–06 Aug · Right: 07–11 Aug

Active Monsoon Suppressing Temperatures — No Heatwave Signal Through 11 Aug

Temperature anomalies across active monsoon zones remain 2–4°C below the long-term mean during Day 1–5, consistent with persistent cloud cover and rainfall over the Gangetic plains, foothills, and northeast India. Northwestern Rajasthan and western Pakistan retain an above-normal signal — the residual heat source that sustains the monsoon trough dynamics. By Day 6–10 the below-normal temperature signal spreads further eastward with the rainfall axis. No heatwave conditions are signalled anywhere in India through 11 August, and no break monsoon pattern is indicated in this run.

Mean 850 hPa Wind (m/s) and speed anomaly vs 1991–2020 LTM · GFS IC 02 Aug 2026 00 UTC · Left: 02–06 Aug · Right: 07–11 Aug

LLJ Active Over Western India, Then Pivoting Into the Bay

The Day 1–5 wind chart shows the Arabian Sea Low-Level Jet (LLJ) sustaining strong westerly/southwesterly flow into western India, with a positive speed anomaly of +3 to +5 m/s over the 20–25°N latitude band. This keeps moisture transport into Rajasthan and the Gangetic plains elevated through early August. The Day 6–10 anomaly pattern reveals the pivotal transition: the above-normal westerly flow over the Arabian Sea and western India weakens and the positive anomaly migrates toward the Bay of Bengal and Northeast India. This 850 hPa signal is the low-level confirmation that the monsoon's next active pulse is being directed into the northeast — not the northwest.

Mean 200 hPa Wind (m/s) and speed anomaly vs 1991–2020 LTM · GFS IC 02 Aug 2026 00 UTC · Left: 02–06 Aug · Right: 07–11 Aug

Exceptional Upper-Level Divergence Signal Over Bay — Strongest of the Season

The 200 hPa chart is the most striking signal in this run. During Day 1–5, the Tibetan High is well-positioned over the plateau and the Tropical Easterly Jet (TEJ) is active across peninsular India — standard active monsoon upper-level structure. The Day 6–10 anomaly, however, shows a +14 to +16 m/s positive speed anomaly over northeast India and the northern Bay of Bengal — among the largest upper-level divergence signals seen this monsoon season. This represents deep tropospheric ventilation: the upper-level anticyclone is strengthening and expanding over the Bay, creating the outflow channel that allows a lower-tropospheric system to develop and intensify without being capped. Combined with the MSLP and 850 hPa signals, the three-level vertical structure for Bay cyclogenesis is assembling in the 07–11 August window.

Deep Depression Recap — Chief Rainfall Driver 29 July–01 August

The Deep Depression that originated over South Chhattisgarh on 29 July and made landfall over the Gujarat/Saurashtra coast by 31 July was responsible for the most intense and widespread rainfall episode of the 2026 monsoon season to date. Over a 72-hour period, it produced:

• Extremely Heavy Rain (≥ 204.5 mm/24h) over South Chhattisgarh and Vidarbha on 29–30 July
• Very Heavy to Extremely Heavy Rain over Madhya Pradesh, northern Maharashtra, and South Gujarat on 30–31 July
• Re-activation of the offshore trough off the South Gujarat coast — the same zone as the 1,064 mm Valsad event of 22–23 July
• Above-normal rainfall anomaly of +60–100 mm across the northwest India belt persisting into early August

The system lacked the Mid-Tropospheric Circulation (MTC) component that made the Valsad event a record extreme — so while South Gujarat received Widespread Very Heavy Rain, the concentrated 1,000+ mm event at a single location was not repeated. Full depression analysis →

Heavy Rain Alert Districts — 02–05 August 2026 (Model Guidance)

Date	State	Key Districts	Alert Level
02 Aug	Northeast India (Assam, Nagaland, Arunachal Pradesh)	Jorhat, Charaideo, Mokokchung, Lower Siang, Longding, Longleng, Kokrajhar, Mon	Very Heavy
02 Aug	Bihar	Supaul, Madhepura	Very Heavy
03 Aug	Uttar Pradesh	Bareilly, Rampur, Sambhal, Gorakhpur	Extremely Heavy Very Heavy
03 Aug	Rajasthan	Karauli, Sawai Madhopur	Extremely Heavy Very Heavy
03 Aug	Chhattisgarh	Koriya	Extremely Heavy
03 Aug	Northeast India (Nagaland, Assam, Arunachal, West Bengal)	Longleng, Tuensang, Mokokchung, Mon, Kokrajhar, Alipurduar	Very Heavy
04 Aug	Bihar	Rohtas, Aurangabad, Buxar, Bhojpur, Katihar	Extremely Heavy Very Heavy
04 Aug	Jharkhand	Ranchi	Extremely Heavy
04 Aug	West Bengal	Bankura	Extremely Heavy
04 Aug	Northeast India (Assam, Arunachal Pradesh, Meghalaya)	Dhemaji, Dibrugarh, Kokrajhar, Bajali, Nalbari, East Siang, Lower Siang, Lower Dibang Valley, Lepa Rada, Lohit, North Garo Hills	Very Heavy
05 Aug	West Bengal	Alipurduar, Maldah, Purba Medinipur, Hooghly, Medinipur West, Nadia	Very Heavy
05 Aug	Uttar Pradesh	Siddharthnagar, Maharajganj	Very Heavy
05 Aug	Uttarakhand	Hardwar, Rudraprayag	Very Heavy
05 Aug	Odisha	Ganjam	Extremely Heavy

Model guidance only — verify against latest IMD district bulletins.

VayuMet Outlook — 02–11 August 2026

02–03 August — Trough Resetting, Northeast and UP Leading

• Northeast India (02–03 Aug): Assam, Nagaland, and Arunachal Pradesh carry the heaviest rainfall during the transition period, independently active from a persistent easterly moisture feed. Jorhat, Mokokchung, Charaideo, and Longleng districts lead with Widely Widespread Very Heavy Rain through both days.
• Uttar Pradesh (03 Aug): The trough axis arrives over western and central UP — Bareilly and Rampur are flagged RED (Extremely Heavy Rain, ≥ 204.5 mm). Gorakhpur active in the eastern sub-Himalayan belt. Fairly Widespread Very Heavy Rain likely across the UP foothills band.
• Rajasthan (03 Aug): Karauli and Sawai Madhopur in eastern Rajasthan see RED alert signals — a residual pulse from the retreating depression trough over Rajasthan before it lifts northward.
• Bihar and sub-Himalayan West Bengal: Beginning to activate from 02–03 Aug with Very Heavy Rain signals; will intensify sharply on 04 Aug.

04–05 August — Bihar Peak and West Bengal Eruption

• Bihar (04 Aug): The rainfall axis reaches Bihar at peak intensity. Rohtas district is flagged RED with a 130 mm/24h signal — the highest single-district value in this run. Aurangabad, Buxar, and Bhojpur (all Magadh/Bhojpur plateau region) also show Widely Widespread Very Heavy Rain. This is a significant flood risk day for southern and central Bihar.
• Jharkhand (04 Aug): Ranchi flagged RED — Jharkhand activates in tandem with Bihar as the trough passes through.
• West Bengal (04–05 Aug): A rapid escalation. Bankura RED on 04 Aug; by 05 Aug the signal explodes across the state — Alipurduar (127 mm), Maldah (97 mm), Purba Medinipur (85 mm), Hooghly (80 mm) all ORANGE. Widely Widespread Very Heavy Rain across 6+ districts on 05 Aug. This is likely related to the early development of the Bay system drawing moisture into West Bengal from the south.
• Uttarakhand (05 Aug): Hardwar and Rudraprayag active with Very Heavy Rain — the Himalayan foothills pick up as the trough consolidates near its northern position.
• Odisha (05 Aug): Ganjam (coastal Odisha) RED — the first sign of the developing Bay system influencing the eastern coast.

07–11 August — Bay of Bengal System Watch

The convergence of signals in this run for the 07–11 August window is striking. Three independent model layers are pointing in the same direction:

• MSLP: Negative anomaly consolidating over the northern Bay — surface low developing
• 850 hPa wind: Flow pivoting from Arabian Sea westerlies into Bay easterlies — low-level convergence over Bay
• 200 hPa: +14 to +16 m/s positive anomaly over NE India/northern Bay — the strongest upper-level divergence signal of the 2026 monsoon season, providing the outflow channel for deep convection to organise

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