Biporjoy: Cyclonic storm develops over Arabian Sea, could make landfall in Pakistan or Oman

Subject: Geography

Section: Physical Geography

Context:

A cyclonic storm “Biporjoy” has developed over the east-central and adjoining southeast Arabian Sea, according to the India Meteorological Department (IMD).

Details:

The IMD predicts a very severe cyclonic storm with a wind speed of 115-125 kmph and gusts of 140 kmph on June 8, 2023.
The European Centre for Medium-Range Weather Forecasts (ECMWF) model, as visualised by the software Windy, shows that the system is moving towards the Sindh province of Pakistan.
Another weather forecast model, Global Forecast System (GFS), predicts a different track. Data visualised by Windy shows that it will likely make landfall in Oman.
Between 1881 and 2019, 41 tropical cyclone systems made landfall in Oman. They have been associated with extreme winds, storm surges and significant flash floods, often resulting in loss of life and substantial damage to infrastructure.
This is the first cyclone to form in June since 2020
The last such cyclone emerged in 2019. Cyclone Vayu flooded low-lying coastal towns in Oman.

Link with the climate change:

The sea surface temperatures in the Arabian Sea are 30-32 degrees Celsius.
This is above the climatological mean. This is clearly the climate change link, as Arabian Sea warming is favouring more intense cyclones.
Delayed monsoon:
- The system will delay the arrival of the southwest monsoon. The system is driving moisture away from India and is hindering monsoon winds.
- There could further cause a delay in the onset and progress of monsoon
- The long-term Indian Ocean warming and the developing El Nino — both have the potential to weaken the monsoon.

Conditions for Formation of Tropical Cyclones:

A consistent source of heat as tropical cyclones are thermally induced low-pressure systems.
Large sea surface with a temperature higher than 27° C which is possible only during the late summers i.e. September, October, and November
Presence of the Coriolis force. It is the result of the earth’s rotation and deflects objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Small variations in the vertical wind speed.
A pre-existing weak low-pressure area or low-level-cyclonic circulation;
Upper divergence above the sea level system.

Cyclonic activities in the Arabian Sea:

Annually, five cyclones on average used to form in the Bay of Bengal and the Arabian Sea combined. Among these, four develop in the Bay of Bengal and one in the Arabian Sea.
Previously, tropical cyclones in the Arabian Sea were restricted to Gujarat. However, now even Kerala and Karnataka have also become more vulnerable to cyclones. A recent example is ‘Ockhi’.
Tauktae is the fourth cyclone in consecutive years to have developed in the Arabian Sea. Cyclone Mekanu hit Oman in 2018, Cyclone Vāyu struck Gujarat in 2019 and Cyclone Nisargahit Maharashtra in 2020.
Apart from frequency, a rise in the intensification rate is also observed. All these cyclones since 2018 have been categorised either ‘Severe Cyclone’ or above.
Tauktae took only 2 days to become Very Severe Cyclonic Storm (VSCS) while Cyclone Mekanu and Cyclone Nisarga had developed slower, taking 4 and 5 days respectively.

Reasons behind increasing cyclonic activities in the Arabian sea:

The sea surface temperatures in the Arabian Sea have increased rapidly during the past century due to global warming. Temp. now is 1.2–1.4 °C higher than the temperature witnessed four decades ago. These warmer temperatures support active convection, heavy rainfall, and intense cyclones.
Therising temperature is also enabling the Arabian Sea to supply ample energy for the intensification of cyclones. Currently, seawater up to depths of 50 metres has been very warm that allowed Cyclone tauktae to become a VSCS in only 2 days.
The Arabian Sea is also providing conducive wind shear for cyclones. For instance, a higher level easterly wind drove the depression of Cyclone Ockhi from the Bay of Bengal to the Arabian Sea.
Greater occurrence of El Niño Modoki. It is a climate phenomenon that means ‘pseudo El Niño’ and creates conditions that are not conducive for cyclogenesis in the Bay of Bengal. However, this condition is conducive for the formation of cyclones in the Arabian Sea.
- El Nino is associated with suppressing cyclone formation in the Arabian Sea.