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No less than three tropical cyclones are currently marching across the western Pacific Ocean, with more possibly in the works. What's behind this sudden surge in storm activity, and what could it mean for Canada?

Typhoon flashmob threatens Asia; potential impact for Canada


Scott Sutherland
Meteorologist/Science Writer

Tuesday, July 7, 2015, 11:24 PM - After a nearly six-week lull, no less than three tropical cyclones are currently marching across the western Pacific Ocean, with more possibly in the works. What's behind this sudden surge in storm activity, and what could it mean for Canada?

Tropical cyclones are by no means unheard of at this time of year. However, after roughly six-weeks of quiet across the Pacific, a small parade of storms has suddenly sprung up, like some kind of a weather-borne flash mob.

While this parade has already produced a deluge of rain for northern regions of the Philippines, and is setting up to make life along the south and southeast coasts of China very interesting by the weekend, the energy of these spinning cyclones may even produce some long-range effects for Canada as the month of July progresses.

Taking a look at these storms, first there's Chan-hom, which started out a week ago - on June 30 - as Tropical Depression 9W. Chan-hom quickly strengthened into a Tropical Storm (earning the storm its name), and even made it to Typhoon strength before weakening slightly on Friday. 

By this time, it was joined by two other cyclones. The first was Linfa, which spun up to the west of Chan-hom as Tropical Depression 10W on Thursday, July 2 and reached Tropical Storm strength by that very night. Further to the east, Nangka started out as Tropical Depression 11W on Friday, July 3, and advanced through Tropical Storm to reach Typhoon strength into Sunday night. Shortly thereafter, Chan-hom encountered warmer waters again, and it restrengthened into a Typhoon.


Credit: earth.nullschool.net

Over the weekend, Linfa swept across the northern part of the Philippines, while Chan-hom and Nangka formed up with it into a potentially-destructive parade of storms. Further to the east, to the south of Hawaii, forecasters are watching at least one more developing storm.

What's behind this parade?

The weather pattern we have to thank for this sudden burst of cyclone activity, after such a long pause, is a large-scale eastward-migrating disturbance known as the Madden-Julian Oscillation, or MJO.

The MJO consists of two phases, each of which spans roughly half the planet at any time. One phase is characterized by enhanced convection, thus it promotes rising air, greater cloud-cover and more rainfall, while the other phase suppresses convection, leaving mainly clear skies and less rainfall.

Prior to the development of these storms, the suppression phase of the MJO was dominant over the Pacific. Even if the other factors in storm formation lined up properly, they would still fight against this suppressed convection, and conditions in the western Pacific, from mid-May to late-June remained free of cyclones. Once that phase moved on, the convective phase moved in to replace it, and the enhanced convection caused storms to erupt across the region.

What's in the forecast?

As of Tuesday, July 7, it appears as though Tropical Storm Linfa will make landfall to the east of Hong Kong sometime on Thursday, and then track across the city on Friday and into Saturday.

Chan-hom looks to be set up for a path that would take it between Okinawa and Taiwan, possibly reaching Super Typhoon strength as it passes them, and reaching the China coast, south of Shanghai, sometime on Saturday. 

Following along behind Chan-hom, Nangka has already reached Super Typhoon status, with maximum sustained wind speeds of 220 km/h, however its path does not appear to threaten China's coast. The storm is moving along quite slowly, and long-range models are projecting that its path will curve, causing it to pass to the north of Guam and possibly press on towards Japan afterward.

If Typhoon Nangka does follow this northerly path, it may become another example of weather teleconnections.

According to Weather Network Chief Meteorologist Chris Scott, in the event of a northward-tracking Nangka, as the storm weakens, its energy could feed into the larger weather pattern over the Pacific Ocean and North America. Just as we saw with Typhoon Nuri in November 2014, the storm's energy may enhance the large-scale ridge of high pressure along the west coast of Canada and the United States, while at the same time setting off small-scale shortwaves along the flow, which would dig a deeper low-pressure trough over the rest of the continent.


Upper-level winds over the Pacific, Nov 7-12, 2014.


Upper-level winds over North America, Nov 7-12, 2014.

Credit: WeatherBell

Thus, in the end, this heightened cyclone activity in the western Pacific could, ultimately, translate into more cooler, wetter weather over the eastern half of North America by the end of July.

Sources: Joint Typhoon Warning Center | NOAA | CIMSS Satellite Blog

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