News Excerpt
Rainfall over the Southern peninsular region has been deficient so far. The India Meteorological Department (IMD) had forecast below normal rainfall over the southern peninsula for the current season.

•    The northeast Indian monsoon (NEM) season is generally defined by the calendar months of October–December, when there is significant rainfall in the southeastern part of peninsular India.
•    In contrast to the southwest Indian summer monsoon (SISM), the NEM contributes only about 11% of the all-India annual rainfall.

About NEM
    The Northeast monsoon occurs during October to December, and is a comparatively small-scale monsoon, which is confined to the Southern peninsula only.
    It is also called the winter monsoon, the rainfall associated with the Northeast monsoon is important for Tamil Nadu, Puducherry, Karaikal, Yanam, coastal Andhra Pradesh, Kerala, north interior Karnataka, Mahe and Lakshadweep.
    After the complete withdrawal of the Southwest monsoon. The wind pattern rapidly changes from the south-westerly to the north-easterly direction.
    The period after the Southwest monsoon season, from October to December, is the peak time for cyclonic activity in the North Indian Ocean region — covering the Arabian Sea and the Bay of Bengal.
    The winds associated with the formation of low pressure systems, depressions, or cyclones influence this monsoon, and therefore, the rainfall.

NEM Season this year
    IMD had forecast below normal rainfall over Tamil Nadu and normal rainfall over the southern peninsula for the current season.
    This year, the Southwest monsoon withdrew completely from the country on October 28, with a delay of a fortnight. On the same day, the IMD declared the onset of the Northeast monsoon over peninsular India. However, rainfall thereafter remained largely subdued and remained below normal till around first week of November.
    IMD’s data records between October-November show significantly below-normal rain over Lakshadweep (-42%), Puducherry (-39%), Tamil Nadu (-25%) and Kerala (-30 %). The majority of districts in Tamil Nadu remain highly rain-deficient.
    South Asian countries such as Maldives and Myanmar, too, record rainfall during October to December. In this season, Sri Lanka also has experienced subdued rain.

Reasons cited for NEM deficiency
    The reason is a prevalent La Niña condition (an abnormal cooling of surface waters), along with a low pressure belt that is currently lying to the north of its normal position. The prevailing La Niña conditions are linked with Pacific Ocean.
    A trough in the easterlies in lower levels is likely to affect the southern peninsula’s rainfall pattern. During years when La Nina conditions prevail, the Northeast monsoon remains below normal.
    La Nina is cooler than normal sea surface temperatures recorded along the East and central Pacific Ocean. It influences rainfall over India.
    The current position of the Inter Tropical Convergence Zone (ITCZ) has also contributed to the poor rainfall during the ongoing monsoon season.  
    La Niña conditions are expected to prevail until early 2021, with some weather models forecasting it to last even till March. As a result, there are high chances that the southern peninsular region may end up with deficient rainfall by the end of the Northeast monsoon season in December.

La Niña link with the Northeast monsoon-
o    While La Niña conditions enhance the rainfall associated with the Southwest monsoon, it has a negative impact on rainfall associated with the Northeast monsoon.
o    During La Niña years, the synoptic systems — low pressure or cyclones — formed in the Bay of Bengal remain significantly to the north of their normal position.
o    Besides, instead of moving westwards, these systems recurve. As they lie to the north of their normal position, not much rainfall occurs over southern regions like Tamil Nadu.

Importance of NEM
The NEM contributes anywhere between 30% and 60% of the annual mean in the provinces of Tamil Nadu, coastal Andhra Pradhesh. Thus, the NEM seasonal rainfall affects the productivity of rice and maize in the provinces of Tamil Nadu and Andhra Pradesh.

Monsoon trough, Pseudo monsoonal tendencies, Monsoon break, Monsoon burst, Retreating Monsoon, Indian Ocean Dipole