Cyclone twins form in the Indian Ocean

11 05 2013

April to June each year usually sees the transition from the southern to the northern hemisphere tropical cyclone season.

During this time it is possible to see cyclones in both hemispheres simultaneously. Furthermore, cyclone ‘twins’ sometimes develop at approximately the same longitude either side of the equator.

For the first time since 2009 cyclone twins have developed in the Indian Ocean.

This was caused by a strong burst of westerly winds along the equator about a week ago. A large mass of clouds located in the same area initially moved eastwards with the wind.

The clouds furthest from the equator then started to curl northwards in the northern hemisphere and southwards in the southern hemisphere due to the earth’s rotation. Over time these cloud masses have consolidated and started to rotate to produce twin tropical storms.

The southern hemisphere storm has been named Jamala and is currently not expected to affect any land areas.

The northern hemisphere storm has been named Mahasen and there is a stronger likelihood of this making landfall next week on one of the Bay of Bengal’s coastal regions.

Regional warnings for Tropical Storm Jamala are produced by the Tropical Cyclone warning Centre at La Réunion in the South Indian Ocean.

Regional warnings for Tropical Storm Mahasen are produced by the Tropical Cyclone Warning Centre at New Delhi, India.

The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance.

You can keep up to date with tropical cyclones around the world on our website or follow us on Twitter.

You can see the latest image of Tropical Storms Jamala and Mahasen at:

http://tropic.ssec.wisc.edu/real-time/indian/images/xxirm5bbm.jpg





Monsoon rains bring devastating floods to southern Pakistan

14 09 2011

Parts of Pakistan and Thailand have seen devastating floods after two weeks of persistent torrential rain. The floods have come at a time when many parts of South Asia expect heavy rainfall as part of the region’s summer monsoon, but it has been particularly heavy for the affected areas and it has come late in the season.

It is usual for monsoon rainfall to vary from year-to-year and for there to be large regional differences in the amount of rain, but what has caused the problems this year?

Observations show there has been a series of low pressure systems passing over Pakistan from northern India over the past two weeks, with little respite in between. This has given no time for water to flow away or seep into the ground, causing a build up of floodwater.

With the rain coming so late in the season, there are indications that the region’s monsoon is continuing beyond its usual length. This means the conditions which persist in a monsoon and bring the heavy rainfall have allowed the low pressure systems to continue to move over the region, bringing the heavy rains with them. It’s not clear why the monsoon would be extended like this, but there is some suggestion that this may be related to knock-on effects from long-term cycles in sea-surface temperatures in the Pacific and Indian Oceans, although it could also be part of the normal year to year variability in the length of the monsoon period.

In 2010, while the flooding was similarly devastating, the reasons behind it were different. This came in the middle of the monsoon season and most of the heaviest rainfall came from a single low pressure system which moved over the region over a period of four or five days. Such low pressure systems aren’t unusual, but in this case it was unusually intense and moved very far to the west – causing the floods. The low pressure system was intense because atmospheric conditions prevailing at the time meant the low pressure dragged in additional warm moist air from the Indian Ocean, intensifying the rains.








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