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I'm teaching a physics class, and I'm getting to the point where we are talking about the Coriolis effect. I usually show a couple of photos/videos showing a storm in the Northern Hemisphere and a storm in the Southern Hemisphere, and talk about why they rotate different directions.

However, it occurred to me that at some point in history, there could well have been two storms occurring in the same ocean but in different hemispheres. Has this ever occurred? This would most likely have to be in the Pacific or Indian Oceans (probably the Pacific, since from what I've gathered the Northern Indian Ocean is less active than most other cyclone basins.) Ideally, a photo/video of this event would exist that I could show my students.

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    $\begingroup$ Coincidentally, as hinted at by a link from gansub, in the Pacific, this has been theorized as a cause or indication of forthcoming El Niño. And it doesn't appear that anyone hit the key point of summary... they form in the western Pacific every 2-5 years, depending on definition (see the Schubert link at the top of gansub's answer), and do occasionally occur in the Indian as well (don't think any of the rare S Atl TC's have matched anything in the N Atl). $\endgroup$
    – JeopardyTempest
    Jul 14, 2016 at 9:16

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It does occasionally happen. Not often, because to kick-start a hurricane there has to be some rotation to start with, from the Coriolis effect, together with a sea surface temperature of >27 °C (+ some other requirements such as lack of horizontal shear). This combination is best met during summer when one or other hemisphere is tilted towards the sun, so the hurricane seasons in both hemispheres tend to be 6 months out of synchronization. But there are occasional overlaps, as in this vector composite, found at http://www.wunderground.com/blog/JeffMasters/archive.html?year=2015&month=06&MR=1 enter image description here

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    $\begingroup$ Here's the source of the image : earth.nullschool.net - It's animated so you might be able to get a better visualisation. Link is for the appropriate date/location $\endgroup$
    – Basic
    Nov 18, 2015 at 16:44
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The formation of twin cyclones does occur in both the Indian Ocean as well as the Western Pacific with the Indian Ocean twins being weaker . Schubert et al Symmetric Twin Tropical Cyclones report that the October through May is the period of formation of twin tropical cyclones with December through February being the maximum frequency. The original definition of twin tropical cyclones was provided by Keen in 1982 Cross Equatorial Pairs in the Southern Oscillation. Apart from high SSTs you also need conditions of intense low level vorticity. The convection associated with the eastward propagating Madden Julien Oscillation(MJO) contains cyclonic Rossby gyres that favour tropical cyclogenesis.

If students are wondering what and where are the cyclonic gyres this image may help in that regard- please pay attention to the cyclonic gyres at the 850 hPa level that trail the convection MJO 3D structure

Lander in Formation of Twin Tropical Cyclone Twins Symmetrical With Respect to the Equator outline the "Keen criteria"

  • The northern and southern systems must initially form within 9 days of each other
  • Latitudinal separation must not be more than 22 degrees
  • The longitudinal difference of the initial disturbances ranged between +9 degrees and -17 degrees

A further strict definition for twins include

  • They must form simultaneously

  • They form at low latitudes (5 degrees above and below the equator)

  • They form along the same longitude

Lander performs case studies for the twin cyclones Lola and Namu in the 1986 Pacific Typhoon season - 1986 Pacific Typhoon Season

A more recent reference Schreck et al. A case study of an outbreak of twin tropical cyclones have performed studies that conclude that a broad and long lasting envelope of warm water, low surface pressure and easterly shear are other conditions that are required for formation of twin cyclones. Students can watch the video in this URL Cyclone Pam and Bavi and see the twin cyclone activity

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To add to Gordon's answer, Cyclone Twenty-five was also called Cyclone Raquel and it was an "off-season" cyclone, as the following reported in the news. It was the first cyclone recorded in the region during July.

The synoptic weather map the region on that day was

West Pacific Weather Map

Source: http://www.bom.gov.au/cgi-bin/charts/charts.view.pl?idcode=IDX0016&file=IDX0016.201506300000.gif

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Today (February 22nd 2019) There are cyclones/typhoons/hurricanes in both the North and South Pacific - Wutip east of Philippines, Oma East of Australia. They are not twin cyclones as defined above, having formed at different times, and being well over 22 degrees of latitude apart. Never seen an asymmetrical pair like this before, maybe a function of increasing sea surface temperatures due to global warming. Link to satellite pictures and text below:

http://www.weatherzone.com.au/news/cyclones-update/529321

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