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The western pacific is on fire at the moment with yet another tropical depression forming this afternoon. There are now 3 simultaneous tropical cyclones in the basin. 11W has winds of 25kts, and is located in the far east of the basin, a couple hundred miles east of the island of Kwajalein. 11W is a compact system which has developed a small central dense overcast feature and spiral banding. If shear remains low enough, I wouldn't be surprised to see rapid strengthening from 11W. The depression is forecast to head west-northwestwards along the south side of the subtropical ridge, and strengthen under low shear and over warm waters.

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<Analyses at 04/12 UTC>

 

Center position                                   :   N11°10'(11.2°)    E167°05'(167.1°)
Direction and speed of movement      :  WNW 30km/h(16kt)
Central pressure                                 :  996hPa
Maximum wind speed near the center :  20m/s(40kt)

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11W became Tropical Storm Nangka and is now at a 50kt intensity according to JTWC. The storm is experiencing moderate shear which is keeping strengthening slow for now. Nangka is expected to become a fairly intense typhoon as it continues to track to the west-northwest.

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Nangka has intensified at a faster rate overnight, and is now a typhoon, with winds of 70kts according to JTWC. Further intensification is expected, with perhaps rapid intensification during the next day or so.

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Nangka is now a cat 2, with winds of 95kts. The eye is clearing out nicely now, and JTWC expect Nangka to become a 130kt super typhoon.

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Nangka continues to strengthen, with winds now at 120kts, cat 4. Further strengthening is expected over the next 24 hours or so, before a turn to the north brings Nangka over cooler waters, initiating weakening.

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After a lull in strengthening and actually a little bit of weakening, Nangka looks like it's intensifying again. Winds are up to 125kts according to JTWC's 3am update, but I think Nangka is a touch stronger than this now.

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Nangka has become the season's fourth Super Typhoon, with winds of 135kts, top end cat 4 on tbe SS scale. There are signs of an eyewall replacement on the way, so Nangka may have peaked. From tomorrow, the upper levels become less favorable so weakening will probably begin at this point anyway.

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Under increased shear, Nangka has weakened, and winds are currently at 105kts, cat 3. The typhoon continues west-northwestwards, but should slow and turn to the north later as Nangka rounds the periphery of the steering ridge to the east. Eventually, ridging over Japan will gain influence and steer Nangka back to the northwest. As this occurs, shear will ease once more, allowing for some re-intensification in the long term.

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Nangka has weakened further, with winds down to 80kts this morning as the typhoon slows and crawls to the north. Shear is impacting the system, but is expected to ease, allowing for some reintensification over the next few days. Some weakening is then expected again on approach to Western Japan, but Nangka is still expected to be a typhoon at landfall.

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Nangka is putting on an impressive second round of intensification. Winds are up to 105kts according to JTWC, cat 3 on the SS scale. Nangka continues to move very slowly northwards in a track well west of Iwo To. Further reintensification is expected, and Nangka is expected to become a category 4 typhoon again before weakening again as it eventually approaches mainland Japan. At already 10 days old and forecast to be around for the next 5 days, Nangka will be a pretty long lived tropical cyclone.

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Nangka underwent another eyewall replacement cycle, which has resulted in winds falling to 90kts sustained according to JTWC. The cycle is now complete and Nangka has a little time to intensify again. Because of the weakening, Nangka probably won't become a category 4 again, but JTWC expect a a third peak of 100kts before weakening begins again on approach to Western Japan.

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An influx of dry air and passage over cooler waters has prevented any further strengthening and has instead caused Nangka to weaken to 85kts. The typhoon is closing in on Western Japan, and should make landfall in a day or so.

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Nangka made landfall earlier today in Skikoku Island, Japan. Nangka is now moving further inland and degrading. Weakened Nangka will recurve to the east soon and dissipate due to further land interaction, high shear and cool sea temperatures in the Sea of Japan.

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Nangka made landfall earlier today in Skikoku Island, Japan. Nangka is now moving further inland and degrading. Weakened Nangka will recurve to the east soon and dissipate due to further land interaction, high shear and cool sea temperatures in the Sea of Japan.

 

Given that Nangka weakened quite a bit before landfall, wind damage seems to have been rather minimal. However, rain impacts were not negligible, given that a measurement site in Japan near Osaka (on the eastern flank of Nangka) measured a total of more than 700 mm (29 inch)!  This rain is causing a high risk of flood damage as well as landslides over the area, which appear to be the primary threat of this system.

 

The Rainbow image below shows that Nangka has lost its strongest convection, and all that remains is an area of rainfall on the southern and eastern side of the system. Still, given that a lot of rain has already fallen in that area, the risk on landslides and flooding will remain.

 

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Rainbow image of Nangka as of July 17, 16:01 UTC. Courtesy: NOAA

 

Sources:

http://www.weather.com/storms/typhoon/news/typhoon-nangka-west-pacific-japan-july2015

http://www.ssd.noaa.gov/PS/TROP/floaters/11W/imagery/rb0-lalo.gif

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