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Typhoon Lan (2017)

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Typhoon Lan (Paolo)
Very strong typhoon (JMA scale)
Category 4 super typhoon (SSHWS)
Typhoon Lan at peak intensity on October 21
FormedOctober 14, 2017
DissipatedCurrently active
(Extratropical after October 23)
Highest winds10-minute sustained: 175 km/h (110 mph)
1-minute sustained: 250 km/h (155 mph)
Lowest pressure925 hPa (mbar); 27.32 inHg
Fatalities3 direct
DamageUnknown
Areas affectedCaroline Islands, Philippines, Japan, South Korea
Part of the 2017 Pacific typhoon season

Typhoon Lan, also known in the Philippines as Typhoon Paolo, was the second largest tropical cyclone in terms of a gale diameter on record,[1] and the most intense of the Northwest Pacific Ocean in 2017, which struck Japan. Lan developed into the twenty-first tropical storm of the annual typhoon season on October 15 and intensified into a typhoon on October 17. It became a large system and turned northward on October 18, yet 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, reaching peak intensity with a large eye late on the same day.

Meteorological history

Map plotting the storm's track and intensity, according to the Saffir–Simpson scale
Map key
Saffir–Simpson scale
  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown
Storm type
triangle Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

The United States Naval Research Laboratory (NRL) initially mentioned a tropical disturbance over Chuuk on October 11.[2] After the slow consolidation, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert to the elongated system early on October 14,[3] shortly after the Japan Meteorological Agency (JMA) started to monitor it as a low-pressure area.[4] 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.[5][6] 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.[7] 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.[8] Early on October 16, the JTWC upgraded Lan to a tropical storm too, based on T-number 2.5 of the Dvorak technique,[9] shortly before it entered the Philippine Area of Responsibility and received the name Paolo from PAGASA.[10]

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 30 ºC with high ocean heat content (OHC) contributed to the intensification,[11] resulting in being upgraded to a severe tropical storm by the JMA at around 00:00 UTC on October 17.[12] Soon, the westward system became quasi-stationary due to a weakening subtropical ridge to the north.[13] When Lan developed into the ninth typhoon of 2017 at around 18:00 UTC,[14] it had turned slowly northward under the steering influence of a building steering ridge to the southeast and east.[13] Early on the next day, the JTWC also upgraded it to a typhoon.[15] although it later became partially exposed for a half of day.[16][17] At around 15:00 on October 18, the JMA reported that Lan had become a large typhoon, with a diameter of about 1,340 km (835 mi).[18] Despite favorable conditions, Lan had struggled to intensity for two days, even while growing larger in diameter.[19]

Lan grew into a very large typhoon with a diameter of about 1,670 km (1,040 mi) early on October 20,[20] and eventually started to rapidly intensify thanks to excellent outflow, particularly poleward, which gradually formed a large and symmetric eye with a diameter of 95 km (60 mi).[21] The JMA indicated that the typhoon had reached its peak intensity at around 18:00 UTC, with the central pressure at 925 hPa (27.32 inHg) and ten-minute maximum sustained winds at 175 km/h (110 mph);[22] the JTWC also reported that Lan had intensified into a super typhoon at the same time.[21] Late on October 22, Lan’s diameter of gale winds expanded to approximately 2,220 km (1,380 mi), making it the second largest tropical cyclone on record.[1]

See also

References

  1. ^ a b Kitamoto, Asanobu. "Typhoon List by Wind Information". Digital Typhoon. Japan Meteorological Agency. Retrieved October 23, 2017.
  2. ^ "Index of /tcdat/tc17/WPAC/25W.LAN/ir/geo/1km". United States Naval Research Laboratory. Retrieved October 21, 2017.
  3. ^ "Tropical Cyclone Formation Alert". Joint Typhoon Warning Center. October 14, 2017. Archived from the original on October 14, 2017. Retrieved October 21, 2017.
  4. ^ "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.
  5. ^ "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.
  6. ^ "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.
  7. ^ "Prognostic Reasoning for Tropical Depression 25W (Twentyfive) Warning Nr 01". Joint Typhoon Warning Center. October 15, 2017. Archived from the original on October 16, 2017. Retrieved October 21, 2017.
  8. ^ "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.
  9. ^ "Prognostic Reasoning for Tropical Storm 25W (Lan) Warning Nr 03". Joint Typhoon Warning Center. October 16, 2017. Archived from the original on October 16, 2017. Retrieved October 21, 2017.
  10. ^ "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.
  11. ^ "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.
  12. ^ "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.
  13. ^ a b "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.
  14. ^ "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.
  15. ^ "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.
  16. ^ "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.
  17. ^ "Prognostic Reasoning for Typhoon 25W (Lan) Warning Nr 13". Joint Typhoon Warning Center. October 18, 2017. Archived from the original on October 18, 2017. Retrieved October 21, 2017.
  18. ^ "WTPQ21 RJTD 181500 RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 18, 2017. Archived from the original on October 18, 2017. Retrieved October 21, 2017.
  19. ^ "Prognostic Reasoning for Typhoon 25W (Lan) Warning Nr 18". Joint Typhoon Warning Center. October 19, 2017. Archived from the original on October 19, 2017. Retrieved October 21, 2017.
  20. ^ "WTPQ21 RJTD 200600 RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 20, 2017. Archived from the original on October 20, 2017. Retrieved October 21, 2017.
  21. ^ a b "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.
  22. ^ "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.
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