Rainfall data of May 2026 of some towns of Sub-Himalayan W Bengal (SHWB) and Sikkim.

May marks the final month of the pre-monsoon season and normally receives 257.5 mm rainfall over the Sub-Himalayan West Bengal (SHWB) and Sikkim region according to IMD (1971–2000 normals). The month is usually characterized by thunderstorms, squalls, hailstorms, and increasing moisture influx from the Bay of Bengal ahead of the southwest monsoon.

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May 2026 was a highly variable month, with rainfall distributed unevenly across the region. Some locations experienced rainfall well above the long-term normal, while others remained comparatively dry.

A notable feature was the occurrence of several intense rainfall events between 13–17 May and again around 22–26 May, particularly affecting Sikkim and parts of the Himalayan foothills.
The extraordinary rainfall which took place in Kalimpong on 28May2026 is covered in an earlier blog.

 Wettest Stations

1. Mangan – 642.3 mm
2. Gangtok – 584.5 mm
3. Sevoke – 440.4 mm
4. Kurseong – 434.2 mm

Driest Stations

1. Khanitar – 92.4 mm
2. Darjeeling – 131.2 mm
3. Kalimpong – 213.0 mm 

Above and Below normals
The IMD normal rainfall for May over SHWB & Sikkim is 257.5 mm. 

Above Normal
Mangan (+149%)
Gangtok (+127%)
Sevoke (+71%)
Kurseong (+69%)
Banarhat (+43%)
Alipurduar (+43%)
Siliguri (+30%)
Damthang (+18%) 

Near Normal 
Neora (−8%) 

Below Normal 
Kalimpong (−17%)
Darjeeling (−49%)
Khanitar (−64%)

Spatial Distribution

Northern Sikkim (see map - Zone 1)

Mangan and Gangtok experienced exceptional rainfall. 

Foothills and the Dooars (see map - Zone 2)

Sevoke, Banarhat, Alipurduar and Siliguri all received abundant rainfall. The foothill belt was particularly active during thunderstorm episodes.

Darjeeling/Kalimpong Hills (see map - Zone 3)

Darjeeling itself was surprisingly dry compared with neighbouring Kurseong and Kalimpong. This highlights the highly localized nature of pre-monsoon convection and terrain-induced rainfall.

Praful Rao
SaveTheHills
savethehills@gmail.com
9475033744

Using the Automatic Weather Station data to understand weather and rainfall (in this case, of Kalimpong)

The rainfall chart for the period May2025 to May2026 for Kalimpong is above and a brief analysis of the same here👇:
a. We had a fairly wet monsoon season (from approx May to Oct2025) characterized by 9 spikes when rainfall exceeded 90mm in a 24hr period. The season did start with some hiccups though:

Typical cloud image over North Bengal and Sikkim before the heavy rain of 19Jun2025

Warning on 13Jul2025 for the heavy rain (112.8mm) on 14Jul2025.

July is typically the wettest month of the monsoon season. In July 2025, there were four days during which rainfall exceeded 90 mm in a 24-hour period. Thereafter, rainfall gradually declined, apart from a brief spike on 12 August 2025. Total rainfall amounted to 467 mm in August and 253.2 mm in September 2025.

October 2025 was relatively dry, except for two days of intense rainfall. On 4–5 October, widespread heavy rain affected the entire region and triggered devastating landslides and flash floods, resulting in significant loss of life in Mirik.

These instances of spikes in rainfall are normally associated with convective clouds and normally consist of short, violent bursts of rainfall which cause high runoff and low infiltration of water (as such no recharge of aquifers) and only result in soil erosion, landslides and damage to roads.

 

After the 2025 monsoons, we went thru an extended 5 month period of drought-like conditions from November2025 to March2026.

Praful Rao
SaveTheHills
savethehills@gmail.com
9475033744 

Rainfall data of March/April 2026 of Sub-Himalayan W Bengal (SHWB) and Sikkim.

Despite the numerous Western Disturbances (WD) hitting the Western Himalayas during the winter of 2026, winter rains for us in the eastern end of the Himalayas were conspicuous by their absence. This was because WDs, which are responsible for our winter precipitation were tracking along higher latitudes or veering off towards the Tibetan plateau as they moved east (see satellite image above) as such never reached the Darjeeling-Sikkim Himalaya.

Forest fires in South Sikkim on 17Feb2026 due to extreme dry weather

In Kalimpong, we received our first storm and rains around mid - March 2026 but the Darjeeling-Kalimpong districts remained largely deficient in rain in Mar2026. 
Sikkim, however received far more rain in March and it is tabulated below:

Rainfall data day-wise for APRIL 2026 of some places in the Darjeeling and Sikkim Himalayas is shown below:

 

 

Location of rain gauge stations and rough zones of rainfall are shown:

Zone 1:  Sikkim, especially North Sikkim, received the heaviest rainfall
Among all areas in the SHWB–Sikkim, the highest precipitation occurred in North Sikkim (Mangan, Lachen, Lachung, Chungthang belt).
Zone 2. Plains of Dooars and Alipurduar were also very wet. The foothill districts of Alipurduar, Jalpaiguri, and the Dooars experienced substantial rainfall due to strong thunderstorm activity and moisture convergence.
Zone 3.  Darjeeling and Kalimpong hills were wet but comparatively less so Although rainfall was above normal, totals in Darjeeling and Kalimpong were generally lower than in North Sikkim and parts of the plains.
And in this region, Kurseong certainly always has the heaviest rainfall. The foothills of the Dooars ie Gorubathan and that belt also have intense thunderstorms and heavy rain.

Graphical Analysis of Rainfall and Windspeed of March and April 2026 of Kalimpong

Praful Rao
SaveTheHills
savethehills@gmail.com
9475033744

Extreme rainfall event in the Eastern Himalayas: 04/05Oct20205 (Part II - 'The damage and fatalities in Nepal and Bhutan')

The October 2025 rains (see previous blog) were among the most intense to strike Eastern Nepal, the Darjeeling Himalayas, and Bhutan in recent years. The storm system, which crept in from northern Uttar Pradesh and Bihar, tracked east-northeast, impacting Eastern Nepal — including Kathmandu — first. The devastation it caused has been extensively covered by the media. Below, we’ve compiled a selection of key excerpts:

Nepal

Rainfall data (mm): Kathmandu 145, Rautahat 330, Ilam 330mm (reported 37 fatalities)

Fatalities, damage and cost:
a. 66 fatalities have been reported, 69 people are missing. 37 people died in Ilam district.
b. Huge damage on development infrastructure like roads, bridges and drinking water projects across Koshi province amounting to Nepalese Rs2.06 billion. Road projects worth about Rs190 million have been lost in Ilam alone.Bridges worth an additional Rs385 million have been destroyed. 226 homes were reported submerged in Kathmandu and a total of 4,059 households affected (ReliefWeb / GDACS summary of national reports).
c. Across Panchthar, Taplejung, Sankhuwasabha, Solukhumbu and Okhaldhunga, dozens of rural roads have been blocked or buried under landslides. Of the 73 roads, 44 still remain completely obstructed, while 12 of 23 motorable bridges have been totally destroyed. A total of 20 suspension bridges remain impassable due to flood damage.

Bhutan

Bhutan lies directly to the east of Kalimpong district (West Bengal) and Sikkim. As the powerful October 2025 storm swept across the Darjeeling–Sikkim Himalayas, it reached Bhutan on 5 October, bringing with it widespread devastation. The rainfall recorded during the event is shown in the map above.
Like Nepal, Bhutan is crisscrossed by several major rivers — Jaldhaka, Diana, Torsa, Sunkosh, Raidak, Jayanti, and Kaljani — which flow from its mountains into the fertile plains of North Bengal and Assam. These rivers are lifelines for irrigation and agriculture in the region. However, intense rainfall in Bhutan’s highlands often translates into dangerous flooding in the plains downstream.

Fatalities and damage reported

As per The Bhutanese, '3 people are likely dead as two persons are reported missing in Haa Dzongkhag due to flash floods in Sertena, Gakiling Gewog and one was washed away in Kazhi in Wangduephodrang. 1 body from Haa was recovered on 6 October 2025 from Cooch Bihar'.
Further '17 bailey bridges, six suspension bridges, three culvert bridges, three wooden bridges and three private bailey bridges were washed away'. Details of the damage are available here.
According to Kuensel, Bhutan’s national newspaper, “across Bhutan, numerous roadblocks, landslides, and washed-out bridges have cut off several communities. The southern and western highways have reported significant disruptions, and several homes have been damaged or flooded.”

One of the most critical impacts was on the country’s extensive hydropower infrastructure. Authorities in North Bengal were placed on high alert after a technical failure at the Tala Hydropower Dam caused it to overflow, sparking fears of downstream flooding in the Dooars region.
In response to the severe weather, five major hydel projects — Tala, Suchhu, Dagachhu, Punatsangchhu, and Chhuka — were temporarily shut down. This unprecedented situation not only disrupted power generation but also highlighted the growing vulnerability of Himalayan infrastructure to extreme weather events.

Further details on the damage to Bhutan’s dams can be found here.

Praful Rao,
SaveTheHills
savethehills@gmail.com
9475033744