Warming oceans challenge Arabian Sea cyclone forecasts

Warming oceans challenge Arabian Sea cyclone forecasts

Subject: geography

Section: Physical geography Climatology

Context: The data suggest that it takes more time for the agency to accurately forecast the trajectory of storms that originate in the Arabian Sea, than those in the Bay of Bengal.

Details:

• Historically, most cyclones around India tend to originate in the Bay of Bengal but global warming is causing the Arabian Sea to be heating up more than average and whetting greater – and increasingly stronger – cyclones like Biparjoy.
• IMD has predicted the path of cyclone Mocha ( a storm of Bay of Bengal) more accurately than that of Cyclone Biporjoy.
• IMD has predicted the path of Cyclone Sitrang, Yaas, Mandous and Gulaab more accurately, all of which are an storm of Bay of Bengal region.
• However IMD failed to predict accurately the path of Arabian sea cyclone Tauktae.

Reason:

• The Bay of Bengal has more frequent cyclones and were better understood.
• The Arabian Sea cyclones, historically have been fewer because of relatively colder sea surface temperatures.
• Nearly 48% of cyclones here never reached land, as opposed to only 13% in the Bay of Bengal.
• There is an increasing prominence of Arabian Sea cyclones with a 52% rise in such cyclones from 2001-2019 and an 8% decrease in those over the Bay of Bengal.
• It is the winds in the upper reaches of the atmosphere, called steering winds, that influence the direction and recurving, whereas the heat within the ocean layers determined the strength and duration of cyclones.
  • While the latter is better captured in the (prediction) models, the wind component is not always fully captured in the models.
• The weather models used to predict the Arabian Sea and Bay of Bengal cyclones were the same and the IMD incorporated inputs from Indian as well as several international models to estimate the track and intensity of cyclones.

There are factors unique to the Arabian Sea, but absent in the Bay of Bengal, which influence a cyclone’s intensity and movement:

• The Arabian Sea has a much deeper – up to 40 metres – layer of warm water compared to that in the Bay of Bengal.
• Many times, these sub-surface values aren’t captured in the cyclone prediction models and that’s why, the strength and speed of the cyclones aren’t accurately captured in advance.