11:30 a.m. Wednesday, Sept. 7, Japan time: When is a typhoon not a typhoon?
That’s been the subject of discussion of late, particularly on social media, regarding Mindulle and Lionrock the past few weeks, and most recently a hybrid storm headed to the Tokyo area; it should cause quite a bit of rain and gusts in the Kanto Plain on Thursday.
Pacific Storm Tracker generally mirrors the Joint Typhoon Warning Center and downline military weather outlets in determining what is and is not a typhoon. Other weather outfits such as the Japan Meteorological Agency use different criteria in determining whether a storm is a typhoon, the numbering and naming of same storms, etc.
As an example: While JMA referred to Mindulle last month as a typhoon, JTWC pegged it as a severe tropical storm. Yet U.S. Forces Japan official social-media pages, even American Forces Network, reported on Typhoon Mindulle, with all the flooding it caused on Yokota Air Base’s east side.
The current system headed toward Tokyo, dubbed Tropical Storm 16-13 (Malou) by JMA, has been acknowledged not even as a tropical system, but only with a tropical cyclone formation alert by the Joint Typhoon Warning Center at 10:30 a.m. local time Tuesday. JTWC re-issued the tropical cyclone formation alert at 10:30 a.m. Wednesday, showing pretty much the same data.
To try to clarify, PST consulted with Tokyo-based international meteorologist Robert Speta, whose reports appear on everything from Japan’s national broadcaster NHK to weather-based social-media groups.
“What you need,” Speta told Stripes in explaining JMA’s criteria, “is a closed-off tropical low with winds of 35 knots (40 mph) or higher. The same as JTWC, only the wind scale for sustained winds is a 10-minute average, instead of a 1-minute average.”
TS 1613 (Malou) did meet JMA’s criteria as a tropical system; in fact, it caused sustained 45-mph sustained winds at a 10-minute threshold, with gusts up to 72 mph at Naha, Okinawa’s prefectural capital.
That would seem to meet JTWC’s criteria for a tropical system. But a closer look at JTWC’s text associated with the tropical cyclone formation alert showed that this system was a “hybrid.” Featured some tropical characteristics, particularly the warmer southern quadrants, and some non-tropical characteristics in the northern quadrants.
Thus, JTWC has not to this point called it a tropical cyclone. And despite winds on Kadena Air Base reaching 43-mph sustained and 52-mph gusts, what’s classified as damaging winds, 58-mph sustained or greater, never took place; thus, U.S. bases on Okinawa remained in seasonal Tropical Cyclone Condition of Readiness 4.
Just as a refresher: Here's the wind criteria used by JTWC, National Weather Service, Central Pacific Hurricane Center and other U.S. agencies to determine what's a tropical depression, tropical storm and/or typhoon/hurricane:
Tropical depression: Up to 38-mph sustained. Tropical storm: 39- to 73-mph sustained. Hurricane/typhoon: 75-mph or above sustained. Super typhoon: 150-mph or above sustained.
Bottom line: It’s not as easy to discern as it may seem.
What is easy to see even from a casual observer’s view, is if it looks dangerous, walks dangerous and quacks dangerous, chances are, the winds and sideways rain are dangerous. And could at some point get worse, blowing vehicles, trampolines, trash cans and other objects around quite easily. Thus, preparation is always key.
Tokyo on Thursday should see winds between 30 and 35 mph with gusts exceeding 40, plus rainshowers, especially from mid-morning to late afternoon. Probably not nearly as bad as Mindulle caused, but still quite nasty. As if the Tokyo area didn’t need any more rain …
11 a.m. Tuesday, Sept. 6, Japan time: A tropical cyclone formation alert has been issued on a disturbance just west of Okinawa that’s projected by computer models to push northeast toward Japan’s main islands in the coming days.
As a result, the weather over Okinawa should remain unpleasant, 60- to 80-percent chance of showers and thunderstorms the next couple of days, with gusty winds overnight into Wednesday. Shoguweather.com forecasts southerly to southwesterly winds 13 to 17 mph gusting up to 34 mph, remaining gusty through Wednesday.