Vongfong – like mother like daughter?

Fortunately, Phanfone turned out not to be a major disaster for Japan. There have been some power outages, some disruption to air travel and other things, and a handful of people killed (mainly due to being in or near the waves at at a bad time, whether the Americans in Okinawa or the surfer in Kanagawa). Nothing to make light of, but not nearly as bad as it could have been.

But it’s not yet time for Japan to relax. The next Typhoon, Vongfong, is spinning its wheels in the tropical western Pacific, and is likely to take almost the same path as Phanfone did, down to the landfall on Honshu, Japan’s big island.

Vongfong is currently estimated to be a category 2 storm, with peak winds of 90 knots, or over 100 mph. It has developed the appearance to go with that intensity, including a proper eye, seen here in the latest visible satellite image:



Track and intensity forecasts for this storm, as for all tropical cyclones in the western Pacific, are issued by the Japan Meteorological Agency (JMA) and the US Joint Typhoon Warning Center. Like the US National Hurricane Center (which produces all our forecasts here in the US for the Atlantic and Eastern Pacific) and other forecast centers worldwide, both agencies issue forecasts out to 5 days. The current track forecasts look quite similar to what Phanfone’s did at this stage. This includes especially the northward turn, scheduled for around 48 hours from now, shown here in the current forecast map from JMA:


While these forecasts have no landfall in them yet, the numerical models seem to be reaching some agreement that Japan is likely to get another one in about a week. Here is a forecast map from NOAA’s GFS model for 00 UTC next Tuesday, October 14. (The recent runs of the ECMWF model look pretty similar.) The map shows surface pressure (contours) together with 500 hPa geopotential height (color shading). Vongfong is the bullseye riding up the east coast of Honshu, interacting with an upper level trough (the southward dip in the ribbons of color) to undergo extratropical transition into a midlatitude cyclone:



Even the intensity forecast (from JTWC) is eerily similar to Phanfone’s. At 90 kt now, Vongfong is forecast to make it up to a 130 kt super typhoon, in the low end of category 4, over the next 48 hours, before starting to weaken again as it moves over cooler waters and higher wind shear. Just how much it weakens is the key question – the phasing with the upper trough in the model run above is just of the right kind to add an extra jolt of energy from the jet stream at landfall. (That’s what happened to Sandy just about two years ago, and in fact the map above would look quite similar to the equivalent one at Sandy’s landfall, if one were to swap North America for Asia.)

Why would two storms develop so similarly, one right after the other?

First, the Western North Pacific has more tropical cyclones per year than any other region on earth. A typical year sees around 90 in the whole earth; the WNP typically accounts for 25 or 30 of those. For our North Atlantic 10 would be about average.

But there’s more to it than just a lot of storms. They do form in bunches sometimes, and it may not be an accident. One typhoon can help generate the next one, when its own spin interacts with the earth’s much larger-scale rotation to produce a “Rossby wave” wake in the atmosphere to its east or southeast – a high pressure, clear weather ridge, followed by another low-pressure trough, typically about 2000-3000 km away, which then is a promising site for another typhoon to form. I haven’t analyzed the early biographies of Phanfone and Vongfong yet to see if they might have been such a “mother-daughter” pair at Vongfong’s genesis, but if they did it wouldn’t be very unusual.

As for the tracks being the same after genesis, that may be just a consequence of the large-scale steering winds not having changed much during the interval between the two storms. It’s fall, the Pacific jet stream should be starting to make its way south, but isn’t far enough south yet for its westerlies to blow the storms back out to sea before they get as far north as Japan.

While those scientific explanations are backed by some research – the links above are to my own research papers, with my former Ph.D. student Kyle Krouse – I don’t think we understand everything we could about the clustering of tropical cyclones in time and space.

Perhaps the most extreme case in (relatively) recent memory was the Atlantic season of 2005, when the hurricanes just kept coming, one after another, long after they had any right to. That was mind-boggling at the time. This current pair in the Pacific may be less so, but it still feels a little spooky.


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