TYPHOON IN-FA

27th July, 2021 Geography

Context

Typhoon In-fa has moved to Shanghai and continued to lash the city after making landfall at the nearby island-city of Zhoushan.

Details

A severe Tropical Storm In-fa is known as a Tropical Storm Fabian in the Philippines.
Storm In-Fa is officially the 7th tropical storm of the 2021 Pacific typhoon season.
It will be the third typhoon after Category 5 Surigae (mid-April) and Category 1 typhoon Champi (late June).

Tropical Storms

Hurricanes, cyclones and typhoons are all types of tropical storms. But are given different names depending on where they appear.
Hurricanes are tropical storms that form over the North Atlantic Ocean and Northeast Pacific.
Cyclones are formed over the South Pacific and Indian Ocean.
Typhoons are formed over the Northwest Pacific Ocean.

Favorable Conditions for Tropical Cyclone Formation

What has fueled the In-fa storm?

Favorable conditions under the MJO over the Pacific Basin have helped the storm to intensify since its birth in the Philippine Sea.
The sea surface temperatures across the western Pacific Ocean are extremely warm, even hot in places this summer.
A large portion of the Philippine Sea and the South China Sea is very hot with sea surface water temperatures 30 to nearly 32 °C (86-88 °F) in some spots.
This is *extremely* supportive of healthy fuel for the deep convective storms.
Strongly anomalous sea temperature often leads to the explosive development of deep storms that develop well-organized tropical cyclones.

Sea Temperature Anomaly

Most of the western Pacific remains with well above-average sea waters.
Sea waters are also warm further west across the South China Sea and towards the Indian Sea.
But the highest sea surface temperature anomalies are observed around Japan and across the Northwest Pacific.
These very warm seas again coincide with another tropical factor that has a huge effect on tropical cyclone activity worldwide. It is known as the MJO – The Madden-Julian Oscillation.

What is the MJO wave?

The Madden-Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales.
The MJO can be characterized as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.
It’s a traversing phenomenon and is most prominent over the Indian and Pacific Oceans.
And the intensity of the MJO wave has recently significantly increased over the Western Pacific and lead to the formation of Typhoon In-Fa.
The MJO has two parts, one side is the enhanced rainfall (we call it the wet phase) and the other side is the suppressed rainfall (we call it a dry phase).
This means that there are increased storms with a lot of rainfall on one side and reduced storm potential and drier weather on the other side.
The wet phase leads to diverging (ascending) air parcels while the dry phase brings converging (descending) air parcels.
This horizontal movement of the air is referred to as the Velocity Potential (VP) in the tropics.

How does MJO affect Indian Monsoon?

The journey of MJO goes through eight phases.
When it is over the Indian Ocean during the Monsoon season, it brings good rainfall over the Indian subcontinent.
On the other hand, when it witnesses a longer cycle and stays over the Pacific Ocean, MJO brings bad news for the Indian Monsoon.
Basically, it is linked with enhanced and suppressed rainfall activity in the tropics and is very important for the Indian monsoonal rainfall.
It has also been established that if the periodicity of MJO is nearly 30 days then it brings good rainfall during the Monsoon season.
If it is above 40 days then MJO doesn't give good showers and could even lead to a dry Monsoon.
Shorter the cycle of MJO, better the Indian Monsoon. Simply because, it then visits the Indian Ocean more often during the four month-long period.
Presence of MJO over the Pacific Ocean along with an El Nino is detrimental for Monsoon rains.

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