Scientists have now discovered why in some years more cyclones form in the Arabian Sea than usual. This is due to a newly discovered Phenomenon (2007) El Nino Modoki.

El Nino Modoki :causes warm moist conditions in the Central Pacific and dry cold conditions in Eastern and western pacific.

El Nino Modoki brings only fewer number of cyclones in the Bay of Bengal because one of the two descending limbs of the Walker Cell is over the western Pacific and Bay of Bengal. The descending limb causes dry conditions not conducive for cyclone formation. The ascending limb of the Walker Cell, on the other hand, brings rain.

El Nino Modoki creates stronger divergence over the western Pacific and Bay of Bengal compared to El Nino. Divergence means surface winds move away from each other and result in low relative vorticity (rotational flow of winds). These conditions are not conducive for cyclones. This explains why Bay of Bengal region (close to western Pacific) has fewer cyclones during an El Nino Modoki.

But there is large convergence over the Arabian Sea during an El Nino Modoki explaining the large number of cyclones in that region.

The number of cyclones per year show significant differences indicating that El Nino Modoki years are conducive for cyclone formation over Arabian Sea while El Nino is conducive for cyclones over the Bay of Bengal.