Typhoon Lan

Typhoon Lan, known in the Philippines as Typhoon Paolo, was the third-most intense tropical cyclone worldwide in 2017. A very large storm, Lan was the twenty-first tropical storm and ninth typhoon of the annual typhoon season. It originated from a tropical disturbance that the United States Naval Research Laboratory had begun tracking near Chuuk on October 11. Slowly consolidating, it developed into a tropical storm on October 15, and intensified into a typhoon on October 17. It expanded in size and turned northward on October 18, although the typhoon struggled to intensify for two days. On October 20, Lan grew into a very large typhoon and rapidly intensified, due to favorable conditions, with a large well-defined eye, reaching peak intensity as a "super typhoon" with 1-minute sustained winds of 250 km/h (155 mph) – a high-end Category 4-equivalent storm – late on the same day. Afterwards, encroaching dry air and shear caused the cyclone to begin weakening and turn extratropical, before it struck Japan on October 23 as a weaker typhoon. Later that day, it became fully extratropical before it was absorbed by a larger storm shortly afterwards.

Typhoon Lan (Paolo)
Typhoon (JMA scale)
Category 4 super typhoon (SSHWS)
Typhoon Lan nearing peak intensity south of Japan on October 21
FormedOctober 15, 2017
DissipatedOctober 23, 2017
Highest winds10-minute sustained: 185 km/h (115 mph)
1-minute sustained: 250 km/h (155 mph)
Lowest pressure915 hPa (mbar); 27.02 inHg
Fatalities17 total
Damage$2 billion (2017 USD)
Areas affectedCaroline Islands, Philippines, Japan, South Korea
Part of the 2017 Pacific typhoon season

Lan caused significant impacts in Japan, with over 380,000 evacuations occurring in Japan, and the cancellations of several domestic flights. In total, approximately 17 deaths were attributed to the typhoon, mainly due to flooding from its rainbands. Damage totals were estimated to have been at least US$2 billion (2017 USD), making it one of the costliest typhoons to have struck Japan.

Meteorological history
Map plotting the track and the intensity of the storm, according to the Saffir–Simpson scale

The United States Naval Research Laboratory (NRL) initially mentioned a tropical disturbance over Chuuk on October 11.[1] After the slow consolidation, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert to the elongated system early on October 14,[2] shortly after the Japan Meteorological Agency (JMA) started to monitor it as a low-pressure area.[3] The agency upgraded it to a tropical depression almost one day later and began to issue tropical cyclone warnings since 06:00 UTC on October 15.[4][5] In the afternoon, the JTWC also upgraded it to a tropical depression assigning the designation 25W, which formative but shallow convective bands had become more organized, and symmetrically wrapped into a defined low-level circulation center.[6] About three hours later, the JMA upgraded it to the twenty-first Northwest Pacific tropical storm in 2017 and assigned the international name Lan, when it was located approximately 310 km (190 mi) to the northeast of Palau.[7] Early on October 16, the JTWC upgraded Lan to a tropical storm too, based on T-number 2.5 of the Dvorak technique,[8] shortly before it entered the Philippine Area of Responsibility and received the name Paolo from PAGASA.[9]

In an area of low to moderate low vertical wind shear, convection over Lan's center was occasionally displaced, but strong poleward outflow enhanced by a tropical upper tropospheric trough (TUTT) as well as sea surface temperature (SST) over 30ºC with high ocean heat content (OHC) contributed to the intensification,[10] resulting in being upgraded to a severe tropical storm by the JMA at around 00:00 UTC on October 17.[11] Soon, the westward system became quasi-stationary due to a weakening subtropical ridge to the north.[12] When Lan developed into the ninth typhoon of 2017 at around 18:00 UTC,[13] it had turned slowly northward under the steering influence of a building steering ridge to the southeast and east.[12] Early on the next day, the JTWC also upgraded it to a typhoon.[14] although it later became partially exposed for a half of day.[15][16] At 12:00 UTC on October 18, the JMA reported that Lan had become a large typhoon, with a diameter of about 1,310 km (815 mi).[17] Despite favorable conditions, Lan had struggled to intensify for two days, even while growing larger in diameter.[17][18]

The eye of Typhoon Lan at peak intensity on October 21

Lan started to rapidly intensify thanks to excellent outflow, particularly poleward, which gradually formed a large and symmetric eye with a diameter of 60 mi (97 km).[19] The JMA indicated that the typhoon had reached its peak intensity at around 18:00 UTC, with the central pressure at 915 hPa (27.02 inHg) and ten-minute maximum sustained winds at 185 km/h (115 mph);[20] the JTWC also reported that Lan had intensified into a super typhoon at the same time.[19] Early on October 21, when Lan accelerated north-northeastward along the western periphery of the deep layered subtropical ridge, the JTWC reported that its one-minute maximum sustained winds reached 250 km/h (155 mph), a high-end category 4 of the Saffir–Simpson scale, ranging from T6.5 to T7.0 of the Dvorak technique.[21] For increasing vertical wind shear, Lan began to weaken and undergo the extratropical transition early on October 22 with significant erosion of its eyewall, after maintaining the super typhoon status as well as peak intensity for over one day. Despite excellent poleward outflow tapping into the mid-latitude westerlies over Japan, the satellite imageries revealed cold-air stratocumulus streaming southward over the western semi-circle of the typhoon, which was associated with advection of cooler, drier air.[22] As the result, the once large eye was quickly filled, and Lan was exhibiting frontal characteristics.[23]

At 03:00 JST on October 23 (18:00 UTC on October 22), Lan made landfall over Omaezaki, Shizuoka Prefecture in Japan,[24] with ten-minute maximum sustained winds at 150 km/h (90 mph) and one-minute maximum sustained winds at 165 km/h (105 mph), equivalent to a Category 2 hurricane.[25] At that time, its diameter of gale winds had expanded to approximately 1,700 km (1,055 mi).[26] Three hours later, Lan weakened to a severe tropical storm.[27] Lan entered the Pacific Ocean shortly before 09:00 JST (00:00 UTC) and continued accelerating northeastward within the westerlies, displaying a well-defined frontal structure with an exposed, broad center and rapidly decaying deep convection sheared to the northeast.[28] The JMA reported that Lan had become extratropical at 06:00 UTC,[29] although the JTWC issued a final warning three hours before and even declared an extratropical cyclone about 12 hours earlier.[28][25] A new extratropical low absorbed the former typhoon late on the same day and explosively intensified into a 934 hPa (27.58 inHg) system east of the Kamchatka Peninsula, on October 24.[30][31][32]

Preparations and impact
Flooding was a prevalent issue for the Kansai region once the rainbands passed, affecting rivers such as the Yodo River here

Ahead of the storm, approximately 381,000 people were evacuated from their homes.[33] Several flights were also cancelled due to the typhoon's impending arrival, and some of Japan's trains were suspended.

In total, 17 people were killed in Mainland Japan and the agricultural loss were about JP¥62.19 billion (US$547.9 million).[34] Total economic losses were counted to be US$2 billion.[35] In the Osaka Prefecture, a train was forced to brake due to part of the railroad having caved in.[33] The typhoon's remnant moisture boosted the intensity of another extratropical cyclone, which later opened up an atmospheric river, contributing to heavy flooding in Alaska from October 24 to 28.[36][37][38]

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See also

References
  1. "Index of /tcdat/tc17/WPAC/25W.LAN/ir/geo/1km". United States Naval Research Laboratory. Retrieved October 21, 2017.
  2. "Tropical Cyclone Formation Alert". Joint Typhoon Warning Center. October 14, 2017. Archived from the original on October 14, 2017. Retrieved October 21, 2017.
  3. "Marine Weather Warning for GMDSS Metarea XI 2017-10-13T18:00:00Z". WIS Portal – GISC Tokyo. Japan Meteorological Agency. October 13, 2017. Retrieved October 21, 2017.
  4. "Marine Weather Warning for GMDSS Metarea XI 2017-10-14T18:00:00Z". WIS Portal – GISC Tokyo. Japan Meteorological Agency. October 14, 2017. Retrieved October 21, 2017.
  5. "WTPQ21 RJTD 150600 RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 15, 2017. Archived from the original on October 15, 2017. Retrieved October 21, 2017.
  6. "Prognostic Reasoning for Tropical Depression 25W (Twentyfive) Warning Nr 01". Joint Typhoon Warning Center. October 15, 2017. Archived from the original on October 15, 2017. Retrieved October 21, 2017.
  7. "WTPQ21 RJTD 151800 RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 15, 2017. Archived from the original on October 15, 2017. Retrieved October 21, 2017.
  8. "Prognostic Reasoning for Tropical Storm 25W (Lan) Warning Nr 03". Joint Typhoon Warning Center. October 16, 2017. Archived from the original on October 17, 2017. Retrieved October 21, 2017.
  9. "Severe Weather Bulletin #2 for Tropical Storm Paolo (Lan)". PAGASA. October 16, 2017. Archived from the original (PDF) on October 21, 2017. Retrieved October 21, 2017.
  10. "Prognostic Reasoning for Tropical Storm 25W (Lan) Warning Nr 06". Joint Typhoon Warning Center. October 16, 2017. Archived from the original on October 16, 2017. Retrieved October 21, 2017.
  11. "Tropical Cyclone Warning for GMDSS Metarea XI 2017-10-17T00:00:00Z". WIS Portal – GISC Tokyo. Japan Meteorological Agency. October 17, 2017. Retrieved October 21, 2017.
  12. "Prognostic Reasoning for Tropical Storm 25W (Lan) Warning Nr 10". Joint Typhoon Warning Center. October 17, 2017. Archived from the original on October 17, 2017. Retrieved October 21, 2017.
  13. "Tropical Cyclone Warning for GMDSS Metarea XI 2017-10-17T18:00:00Z". WIS Portal – GISC Tokyo. Japan Meteorological Agency. October 17, 2017. Retrieved October 21, 2017.
  14. "Typhoon 25W (Lan) Warning Nr 011". Joint Typhoon Warning Center. October 17, 2017. Archived from the original on October 17, 2017. Retrieved October 21, 2017.
  15. "Prognostic Reasoning for Typhoon 25W (Lan) Warning Nr 12". Joint Typhoon Warning Center. October 18, 2017. Archived from the original on October 18, 2017. Retrieved October 21, 2017.
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  17. Typhoon Lan (PDF) (Report). Best track data. Tokyo, Japan: Japan Meteorological Agency. December 18, 2017. Retrieved March 17, 2018.
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  19. "Prognostic Reasoning for Super Typhoon 25W (Lan) Warning Nr 22". Joint Typhoon Warning Center. October 20, 2017. Archived from the original on October 20, 2017. Retrieved October 21, 2017.
  20. "Tropical Cyclone Warning for GMDSS Metarea XI 2017-10-20T18:00:00Z". WIS Portal – GISC Tokyo. Japan Meteorological Agency. October 20, 2017. Retrieved October 21, 2017.
  21. "Prognostic Reasoning for Super Typhoon 25W (Lan) Warning Nr 23". Joint Typhoon Warning Center. October 21, 2017. Archived from the original on October 21, 2017. Retrieved October 26, 2017.
  22. "Prognostic Reasoning for Typhoon 25W (Lan) Warning Nr 27". Joint Typhoon Warning Center. October 22, 2017. Archived from the original on October 22, 2017. Retrieved October 26, 2017.
  23. "Prognostic Reasoning for Typhoon 25W (Lan) Warning Nr 28". Joint Typhoon Warning Center. October 22, 2017. Archived from the original on October 22, 2017. Retrieved October 26, 2017.
  24. Kitamoto, Asanobu. "台風201721号の全般台風情報一覧". Digital Typhoon (in Japanese). Japan Meteorological Agency. Retrieved October 26, 2017.
  25. "Typhoon 25W (Lan) Warning Nr 30". Joint Typhoon Warning Center. October 22, 2017. Archived from the original on October 22, 2017. Retrieved October 26, 2017.
  26. Kitamoto, Asanobu. "Typhoon List by Wind Information". Digital Typhoon. Japan Meteorological Agency. Retrieved October 23, 2017.
  27. "WTPQ21 RJTD 222100 RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 22, 2017. Archived from the original on October 22, 2017. Retrieved October 26, 2017.
  28. "Typhoon 25W (Lan) Warning Nr 31". Joint Typhoon Warning Center. October 23, 2017. Archived from the original on October 23, 2017. Retrieved October 26, 2017.
  29. "WTPQ21 RJTD 230600 RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 23, 2017. Archived from the original on October 23, 2017. Retrieved October 26, 2017.
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  33. Wright, Pam (October 23, 2017). "Typhoon Lan Clobbers Japan With 100+ MPH Winds, Killing 2". The Weather Channel. Retrieved December 24, 2017.
  34. "平成29年台風第21号による被害状況". Ministry of Agriculture, Forestry and Fisheries. December 7, 2017. Retrieved December 27, 2017.
  35. "Companion Volume to Weather, Climate & Catastrophe Insight" (PDF). Aon Benfield. Retrieved January 30, 2018.
  36. "NASA examines heavy rainfall generated by former Typhoon Lan". Phys.org. October 24, 2017. Retrieved October 28, 2017.
  37. "Weather Service issues flood watch". Phys.org. October 26, 2017. Retrieved October 28, 2017.
  38. "Flood warning for Jordan Creek". KINY. Retrieved October 28, 2017.
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