Was there a cloud burst in Sikkim on 03Oct2023?

The media is howling about a cloud burst that occurred in North Sikkim around the 03Oct2023 and which triggered the GLOF (Glacial Lake Outburst Flood) at South Lhonak lake, which led to the terrifying devastation in Sikkim and Kalimpong district on 04Oct 2023.

To get to the truth of the matter let us first see what is a cloud burst:
As per IMD
'If 100mm rainfall is received at a station in one hour, the rain event is termed as cloud burst.'

Placed below is a map and the rainfall data of North Sikkim (and Gangtok) and of Darjeeling and Kalimpong for the period 01Oct to 04Oct2023.

What is apparent is that Darjeeling and Kalimpong received far more rain than North Sikkim during this period and to support this are placed the Infra Red cloud images of 03Oct2023. Sikkim

It is highly unlikely that the type of clouding seen in the vicinity of Lhonak glacier would trigger a cloud burst since such high intensity rain is normally associated with convective clouding and cumulonimbus (CB) clouds which generate a distinct white signature in IR satellite images.
What are cumulonimbus (CB) clouds and how do they appear on IR satellite images?

How CB clouds appear on satellite imagery

There is no doubt that a GLOF did occur at South Lhonak glacier on 03/04Oct2023 between midnight and around 1am on 04Oct2023 - satellite imagery and reports from people at Lachen confirm this.
However, the widely held belief that a cloudburst triggered the GLOF is probably incorrect and maybe ascribed to media loosely calling any 'heavy rain' event a 'cloud burst' just as many issues these days are conveniently labelled under the banner 'climate change' without any verification.

So if a cloudburst did not trigger the GLOF, just what did?

That is a question which has still not been answered.

Praful Rao
Kalimpong district
Darjeeling-Sikkim Himalaya
savethehills@gmail.com
9475033744

Highly localized, extreme rainfall in Kalimpong :01Aug2023

With a deep depression in the north Bay, 01Aug2023 started off in North Bengal and Kalimpong as a warm, dry day and remained so most of the day. There was little indication of the severe weather which was looming in the evening and IMD had issued only a YELLOW warning for our region.
The first patches of cumulonimbus clouds appeared in the satellite image at 5.45pm.

Thundershowers started around 6.30pm and continued nonstop till 11.30pm. Rainfall intensities remained high as can be seen from the graph.

What was very surprising was that the rainfall was very localized with the precipitation only occurring in Kalimpong. Other towns in the vicinity had the normal expected rain - only Jhalong and Rongo in the far east of Kalimpong district showed the extreme rain as was experienced in Kalimpong.

Even though landslides did occur, their prevalence was not high - perhaps because of the meagre rainfall received in north Bengal in the latter half of Jul2023 and the consequent decrease in the moisture content of the soil.

Praful Rao
Kalimpong district
Darjeeling Sikkim Himalaya
savethehills@gmail.com
9475033744

STH stormwatch : Reporting a Low Pressure Area in the Bay of Bengal (11Aug2015)

See here for further information

Praful Rao,
Kalimpong,
Dist Darjeeling

STH Stormwatch : Last update on storm for 02Aug2015

1.In the absence of more detailed information from IMD websites (which seem to be on an extended weekend holiday) through the day , I have placed above :-
a. Satellite image from Nepal MFD which shows the storm position at approx 8.00pm IST.
b. Image of lightning (blue dots - associated severe weather in thundershowers and rain) in the entire south Asian region from the University of Washington at approximately the same time.
The lightning position in India coincides with the storm position.( The red stars in the lower image indicate position of the ground stations for lightning detection)
2. The absence of clouding from south Bengal as compared to previous image should come as a huge relief to most of us.

Praful Rao,
Kalimpong,
Dist Darjeeling

STH stormwatch (31Dec2014) : Update on well marked Low Pressure Area in Bay of Bengal

Praful Rao,
Kalimpong,
Dist Darjeeling

Rainfall data (May2014) and tracks/timeline of a depression (22May-28May2014)

• As per IMD, Sub-Himalayan West Bengal and Sikkim is running 27% deficient in rainfall for the period 01Mar-28May2014 (Slide 1).
• Actual rainfall figures, date-wise are given in Slide 2.
• In our 'Storm Watch' series, STH reported a storm in the Bay of Bengal on 20May2014 and tracked it upto 28May2014 when it reached the Darjeeling-Sikkim Himalaya resulting in a 12hr spell of rain in our region. Luckily, the rainfall though continuous, was not heavy.Tracks and rainfall associated with the disturbance can be seen in Slides 3 & 4.
• No landslide fatality is reported in May2014 and all landslides in this region were confined to North Sikkim and along roads.
  
  
  Praful Rao,
  Kalimpong,
  Dist Darjeeling

Satellite Imagery : How reliable is it for rainfall / adverse weather prediction?

Satellite Imagery (both Vis and IR) is an invaluable tool for the lay person to obtain information on the formation,development and movement of weather systems. It has been a part of the STH blog for the past 3 yrs and is an integral part of the "STH Stormwatch" series in which we monitor weather systems that form in the Bay of Bengal.
This information, earlier only available to scientists and meteorologists is now available to anyone with internet connectivity. Having said this however, it  is not advisable to depend on satellite images exclusively as a method to predict rainfall / adverse weather, the next few images will explain why :

Thus it is clear that satellite images though vital for early warning CANNOT give foolproof warnings. For those interested the link to the Darjeeling "Hurricane" is here.

Rohan Rao,
Kalimpong,
Dist - Darjeeling,
E-mail - rohan.rao1313@gmail.com

The Low Pressure is upgraded to a Depression

                     

Bulletin Number : BOB 03/2012/01      

Dated: 17.11. 2012
Time of issue: 1400 hours IST

               Sub: Depression over east central Bay of Bengal

Latest satellite imagery and current Buoy observations indicate that a depression has formed over east central Bay of Bengal and lay centred at 1130 hrs IST of today, the 17thth November 2012 near latitude 15.50N and longitude 90.00E, about 1050 km east-northeast of Chennai (Tamilnadu), 750 km east-southeast of Visakhapatnam and 650 km southeast of Paradip. 

The system would intensify into a deep depression and move slowly northwestwards during next 24 hrs. It would move west/west-southwestwards towards south Andhra Pradesh and north Tamil Nadu coasts during subsequent 48 hrs.
Under the influence of this system, rainfall at most places with isolated heavy rainfall would occur over Andaman and Nicobar Islands during next 24 hrs.

No adverse weather is likely along and off east coast of India during next 48 hrs. However, Fishermen along north Tamil Nadu and Andhra Pradesh coasts are advised to be cautious while venturing into sea during this period.
The next bulletin will be issued at 2030 hrs IST of today, the 17th November, 2012

You can read the next bulletin here

Praful Rao

STH Stormwatch : Update on storm in Bay of Bengal (17Nov2012)

On 13Nov2012 STH reported the formation of a low pressure in the Bay of Bengal; today the storm has intensified into a "well-marked low with an associated cyclonic circulation upto 3.6km".
The storm which is also being reported by the U.S Navy's Joint Typhoon Warning Center is likely to intensify further.

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For anyone interested in knowing how severe weather systems are classified :-

Classification of cyclonic disturbances and tropical cyclones

1. Low or Low pressure area

2. Depression or tropical depression

3. Deep depression

4. Cyclonic storm

5. Severe cyclonic storm

6. Very severe cyclonic storm

7. Super cyclonic storm

Praful Rao