The forecasts from IMD scientists would primarily be based on Madden Julian oscillation. This phenomenon is an equatorial traveling pattern of anomalous rainfall that is planetary in scale.

Behavior

The Madden-Julian Oscillation (MJO) is the dominant component of the intra-seasonal variability in the tropical atmosphere. It consists of large-scale coupled patterns in atmospheric circulation and deep convection. It comes with coherent signals in many other variables, all propagation eastward slowly through the portion of the Indian and Pacific oceans. Here the sea surface is warm. It constantly interacts with the underlying ocean and influences many weather and climate systems.

Its large-scale and multi-scale structures are described in a better way now. Its scale interaction is also recognized over the years with persistent observations. Its broad influences on tropical and extra tropical weather and climate are increasingly appreciated looking at its role in enhancing monsoon. Its mechanisms for disturbing the ocean are further realised. Yet the MJO remains an unmet challenge to our understanding of the tropical atmosphere and to our ability to simulate and predict its variability.

The Madden-Julian oscillation (MJO) is an equatorial traveling pattern of anomalous rainfall that is planetary in scale. The MJO is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian Ocean and Pacific Ocean. The anomalous rainfall is usually first evident over the western Indian Ocean, and remains evident as it propagates over the very warm ocean waters of the western and central tropical Pacific. This pattern of tropical rainfall then generally becomes very nondescript as it moves over the cooler ocean waters of the eastern Pacific but reappears over the tropical Atlantic and Indian Ocean. The wet phase of enhanced convection and precipitation is followed by a dry phase where thunderstorm activity is suppressed. Each cycle lasts approximately 30-60 days. Because of this pattern, The MJO is also known as the 30-60 day oscillation, 30-60 day wave, or intra-seasonal oscillation.

It propagate eastward across the equatorial Indian and western/central Pacific oceans, with a local intra-seasonal period of 30-90 days. This phenomenon- Madden-Julian Oscillation (MJO) was first documented by Madden and Julian 1971, 1972 the MJO has intrigued many atmospheric scientists and oceanographers all over the world. There are distinct patterns of lower-level atmospheric circulation anomalies which accompany the MJO-related pattern of enhance or decreased tropical rainfall across the tropics. These circulation features extend around the globe and are not confined to only the eastern hemisphere. The Madden-Julian oscillation moves eastward at 5 meters per second (11 mph) across the tropics, crossing the Earth's tropics in 30 to 60 days, with the active phase of the MJO tracked using the degree of outgoing long wave radiation which is measured by infrared-sensing geostationary weather satellites. The lower the amount of outgoing long waves radiation, the stronger the thunderstorm complexes, or convection, is within that region.

Enhanced surface westerly winds occur near the east side of the ocean surface, follow in phase with the east-wind component of the surface winds. In advance, or to the west of the enhanced rainfall area, winds aloft are easterly. These wind changes aloft are due to the divergence present over the active thunderstorms during the enhanced phase. Its direct influence can be tracked pole ward as far as 30 degrees latitude from the equator in both northern and southern hemispheres, propagating outward from its origin near the equator at around 1degree latitude, or 111 kilometers (69 mi), per day.

Local effects - Connection to the monsoon

During the Northern Hemisphere summer season the MJO-related effects on the Indian summer monsoon are well documented. MJO-related effects on the North American summer monsoon also occur, though they are relatively weaker. A strong relationship between the leading mode of intra-seasonal variability of the North American Monsoon System, the MJO and the points of origin of tropical cyclones is also present.

Periods of warming sea surface temperatures are found five to ten days prior to a strengthening of MJO-related precipitation across southern Asia. A break in the Asian monsoon, normally during the month of July, has been attributed to the Madden-Julian oscillation, after its enhanced phase moves off to the east of the region into the open tropical Pacific Ocean.

Influence on Tropical Cyclogenesis

Although tropical cyclones occur throughout May-November in both the north Pacific and the north Atlantic basins, in any given year there are periods of enhanced/ suppressed activity within the season. There is evidence that the MJO modulates this activity (particularly for the strongest storms) by providing a large scale environment that is favourable (or unfavourable) for development. MJO-related descending motion is not favourable for tropical storm development. However, MJO-related ascending motion is a favourable pattern for thunderstorm formation within the tropics, which is quite favourable for tropical storm development. As the MJO progresses eastward, the favoured region for tropical cyclone activity also shifts eastward from the western pacific to the eastern Pacific and finally to the Atlantic basin.

There is an inverse relationship between tropical cyclone activity in the western north Pacific basin and the north Atlantic basin, however. When one basin is active, the other is normally quiet, and vice versa. The main reason for this appears to be the phase of the Madden-Julian oscillation, or MJO, which is normally in opposite modes between the two basins at any given time. While this relationship appears robust, the MLO is one of the many factors that contribute to the development of tropical cyclones.