Private weather forecaster Skymet has said that it
expects the 2019 monsoon rains to be “below normal”. It expects monsoon rains
to be about 7% short of the long period average rainfall (89cm) that India receives
from June to September. It has also predicted the onset of monsoon to be late.
The general duration of the monsoon in India is
between 100-120 days from early June to mid-September. The monsoon arrives at
the southern tip of the Indian peninsula generally by the first week of June.
Skymet has predicted that there is a 15% chance
of a drought, 30% chance of normal rainfall and 55% chance of below normal
Normal rainfall is when the percentage departure
of realised rainfall is within ± 10 % of the Long Period Average (LPA). Below normal
rainfall is when percentage departure of realised rainfall is < 10% of the LPA.
Drought is when the seasonal rainfall is less than 90% of the LPA.
Skymet attributed developing El Nino phenomenon
for its forecast of below normal rainfall during the monsoon. El Nino refers to
the large-scale ocean-atmosphere climate interaction linked to a periodic warming
in sea surface temperatures across the central and east-central Equatorial
Pacific. It is the periodic development of a warm ocean current along the coast
of Peru as a temporary replacement of the cold Peruvian current.
A strong El Nino results in reduction and uneven
distribution of rainfall across the Indian sub-continent. This is because the
trade winds coming from South America which normally blow westward towards Asia
during Southwest Monsoon gets weakened due to the warming of the Pacific Ocean.
Therefore, moisture and heat content gets limited and this leads to poor
rainfall in the region.