User:RandomInfinity17/Tropical Storm Namtheun (2021)

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Severe Tropical Storm Namtheun
Namtheun at peak intensity in the open Pacific on October 16
Meteorological history
FormedOctober 8, 2021 (2021-10-08)
ExtratropicalOctober 17, 2021 (2021-10-17)
DissipatedOctober 22, 2021 (2021-10-22)
Severe tropical storm
10-minute sustained (JMA)
Highest winds95 km/h (60 mph)
Lowest pressure996 hPa (mbar); 29.41 inHg
951 hPa (mbar); 28.11 inHg while extratropical[1]
Tropical storm
1-minute sustained (SSHWS/JTWC)
Highest winds100 km/h (65 mph)
Lowest pressure996 hPa (mbar); 29.41 inHg
Overall effects
FatalitiesNone
DamageMinimal
Areas affectedPacific Northwest, California, British Columbia
Part of the 2021 Pacific typhoon season

Severe Tropical Storm Namtheun was a strong tropical storm that affected the Pacific Northwest and British Columbia as a powerful extratropical cyclone. It was the first of three systems that impacted the Pacific Northwest in late October 2021.[2] The 36th tropical depression, and 19 tropical storm of the 2021 Pacific typhoon season, Namtheun began as an area of convection approximately 333 miles (535 km) southwest of Wake Island on October 8. The JMA recognized it as a tropical depression the next day with the JTWC issuing a Tropical Cyclone Formation Alert (TCFA) at the same time. By midnight, the depression was named Namtheun. Namtheun continued to move west for the next two days before weaking back into a tropical depression due to a subtropical ridge. The storm then started to move to the northeast before strengthening back into a tropical storm on October 13. Namtheun continued to move to the northeast before peaking as a severe tropical storm with winds of 100 km/h (60 mph) on October 16 soon before turning into an extratropical cyclone.

As a tropical cyclone, Namtheun never affected any landmasses. However, the extratropical remnants brought heavy rains and wind gusts of up to 35 miles per hour (56 km/h) in the Pacific Northwest and British Columbia. However, only minimal damage was reported.

Meteorological history[edit]

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

On October 8, the Joint Typhoon Warning Center (JTWC) noted an area of convection persisted approximately 289 nmi (535 km; 333 mi) from Wake Island, that had a medium chance a development.[3] The next day, the Japan Meteorological Agency (JMA) recognized the system as a tropical depression.[4] At 14:00 UTC the same day, the JTWC issued a TCFA for the invest as it developed a significant convection around the center.[5] By midnight on October 10, the JMA upgraded it to a tropical storm and named it Namtheun, which comes from the Nam Theun river in Laos.[6][7] The JTWC soon after upgraded the system to a tropical depression, then a tropical storm at 09:00 UTC.[8][9] Namtheun managed to maintain its intensity for two days until October 13, when it was downgraded to a tropical depression by the JTWC, as it started moving westwards because of the presence of a subtropical ridge towards the southeast.[10] However, at 15:00 UTC of the next day, the JTWC re-upgraded it to a tropical storm, as it entered over warm sea-surface temperatures which allowed the system to gain it intensity despite the presence of high wind shear. Satellite imagery indicated that the storm exhibited subtropical characteristics.[11] Unexpectedly, Namtheun further intensified into a severe tropical storm according to JMA at 06:00 UTC on October 16, and a Category 1-equivalent typhoon according to JTWC at 09:00 UTC the same day.[12][13][nb 1] Satellite imagery depicted that the system had developed an eye-like structure in the core of the storm. The weakening of the vertical wind shear was main reason for the unexpected intensification.[14] A few hours later, the cooling of sea surface temperatures and increasing wind shear caused the storm to weaken further from its peak intensity.[15][16] Namtheun managed to maintain its intensity as it continued north-northwards before it started its extratropical transition between 00:00 and 15:00 UTC on October 17.[17][18] For the next several days, the extratropical remnants of Namtheun moved eastward across the North Pacific, before undergoing explosive intensification and developing into a bomb cyclone on October 21, reaching an extratropical peak of 951 millibars (28.1 inHg), while off the coast of the Pacific Northwest.[19] Afterward, the system curved northward and then north-northwestward, while gradually weakening, before being absorbed into another extratropical cyclone from the west, late on October 22.[20]

Preparations, impacts, and notability[edit]

Namtheun as a hurricane-force extratropical cyclone on October 21

Namthuen stayed over open ocean and didn't affect land as a tropical cyclone.

The extratropical remnants of Namthuen was the first of three systems to affect the western coast of Canada and the United States in late October of 2021. The National Weather Service (NWS) issued storm warnings and gale warnings off the coast of the Pacific Northwest on October 21.[21] The storm was expected to bring up to 5 inches (130 mm) of rain to the Santa Cruz Mountains and up to 8 inches (200 mm) to the North Bay.[22]

The storm carried a category 5 atmospheric river to the region, bringing most rainfall in nine months.[23] Minimal thunderstorms were observed on the Oregon and Washington coasts on October 21.[24] Over 16,000 customers lost power in California alone with another 3,000 in Washington.[25] Along with another powerful system, the rainfall effectively put an end to the state's wildfire season of the year.[26]

Namthuen, along with the other storms in late-October, was unusual for its low pressure. At peak intensity as an extratropical cyclone, it had a pressure of 951 millibars (28.1 inHg). The lowest pressure on record at the time in the area was around 950 millibars (28.05 inHg). However, the following system would become the most intense storm in the region on record at 942 millibars (27.8 inHg).[27][28]

See also[edit]

Notes[edit]

  1. ^ In post-season analysis, Namtheun was downgraded to a tropical storm by JTWC/JMA best track data.

References[edit]

  1. ^ "WPC Surface Analysis valid for 10/21/2021 at 15 UTC". wpc.ncep.noaa.gov. Weather Prediction Center. October 21, 2021. Archived from the original on October 28, 2021. Retrieved October 28, 2021.
  2. ^ "Fascinating 'bomb cyclone' to put on show out in Pacific Ocean". FOX 13 Seattle. 2021-10-20. Retrieved 2022-09-17.
  3. ^ Significant Tropical Weather Advisory for the Western and the South Pacific Oceans Reissued (Report). United States Joint Typhoon Warning Center. 8 October 2021. Archived from the original on October 8, 2021. Retrieved 10 October 2021. Alt URL
  4. ^ "JMA Warning and Summary 090600". Japan Meteorological Agency. October 9, 2021. Archived from the original on October 9, 2021. Retrieved October 10, 2021.
  5. ^ Tropical Cyclone Formation Alert (Invest 95W) (Report). United States Joint Typhoon Warning Center. 9 October 2021. Archived from the original on October 9, 2021. Retrieved 10 October 2021. Alt URL
  6. ^ "RSMC Prognostic Reasoning No. 3 for Tropical Storm Namtheun (2119)". Japan Meteorological Agency. October 10, 2021. Archived from the original on October 10, 2021. Retrieved October 10, 2021.
  7. ^ "Meaning of Tropical Cyclone Names". www.hko.gov.hk. Retrieved 2022-11-24.
  8. ^ Prognostic Reasoning for Tropical Depression 23W (Namtheun) Warning No. 1 (Report). United States Joint Typhoon Warning Center. 10 October 2021. Archived from the original on October 10, 2021. Retrieved 10 October 2021.
  9. ^ Prognostic Reasoning for Tropical Storm 23W (Namtheun) Warning No. 2 (Report). United States Joint Typhoon Warning Center. 10 October 2021. Archived from the original on October 10, 2021. Retrieved 10 October 2021. Alt URL
  10. ^ Prognostic Reasoning for Tropical Storm 23W (Namtheun) Warning No. 2 (Report). United States Joint Typhoon Warning Center. 10 October 2021. Archived from the original on October 10, 2021. Retrieved 10 October 2021. Alt URL
  11. ^ Prognostic Reasoning for Tropical Storm 23W (Namtheun) Warning No. 19 (Report). United States Joint Typhoon Warning Center. 14 October 2021. Archived from the original on October 14, 2021. Retrieved 15 October 2021. Alt URL
  12. ^ "RSMC Prognostic Reasoning No. 28 for Severe Tropical Storm Namtheun (2119)". Japan Meteorological Agency. October 16, 2021. Archived from the original on October 16, 2021. Retrieved October 16, 2021.
  13. ^ Prognostic Reasoning for Typhoon 23W (Namtheun) Warning No. 26 (Report). United States Joint Typhoon Warning Center. 16 October 2021. Archived from the original on October 16, 2021. Retrieved 16 October 2021.
  14. ^ Prognostic Reasoning for Typhoon 23W (Namtheun) Warning No. 26 (Report). United States Joint Typhoon Warning Center. 16 October 2021. Archived from the original on October 16, 2021. Retrieved 16 October 2021.
  15. ^ "RSMC Prognostic Reasoning No. 29 for Tropical Storm Namtheun (2119)". Japan Meteorological Agency. October 16, 2021. Archived from the original on October 16, 2021. Retrieved October 18, 2021.
  16. ^ Prognostic Reasoning for Tropical Storm 23W (Namtheun) Warning No. 27 (Report). United States Joint Typhoon Warning Center. 16 October 2021. Archived from the original on October 16, 2021. Retrieved 18 October 2021. Alt URL
  17. ^ "RSMC Tropical Cyclone Advisory". Japan Meteorological Agency. October 17, 2021. Archived from the original on October 17, 2021. Retrieved October 18, 2021.
  18. ^ Tropical Storm 23W (Namtheun) Warning No. 31-FINAL (Report). United States Joint Typhoon Warning Center. 17 October 2021. Archived from the original on October 17, 2021. Retrieved 18 October 2021. Alt URL
  19. ^ "WPC Surface Analysis valid for 10/21/2021 at 15 UTC". wpc.ncep.noaa.gov. Weather Prediction Center. October 21, 2021. Archived from the original on October 28, 2021. Retrieved October 28, 2021.
  20. ^ "WPC Surface Analysis valid for 10/22/2021 at 21 UTC". wpc.ncep.noaa.gov. Weather Prediction Center. October 22, 2021. Archived from the original on October 28, 2021. Retrieved October 28, 2021.
  21. ^ "National Weather Service". www.weather.gov. National Weather Service. October 21, 2021. Archived from the original on October 21, 2021. Retrieved November 24, 2022.
  22. ^ "Atmospheric river storms to soak Bay Area, Northern California — biggest in 9 months". The Mercury News. 2021-10-19. Retrieved 2022-11-24.
  23. ^ "Atmospheric river storms to soak Bay Area, Northern California — biggest in 9 months". The Mercury News. 2021-10-19. Retrieved 2022-11-24.
  24. ^ "Storm Prediction Center Oct 21, 2021 0600 UTC Day 1 Convective Outlook". www.spc.noaa.gov. Retrieved 2022-11-24.
  25. ^ "PowerOutages on October 22, 2021". poweroutages.us. Power Outages.us. October 22, 2021. Archived from the original on October 22, 2021. Retrieved November 24, 2022.
  26. ^ David Knowles (October 25, 2021). "Record-breaking California bomb cyclone linked to climate change". Yahoo News. Archived from the original on October 26, 2021. Retrieved November 4, 2021.
  27. ^ "U.S. Readies For 'Strongest Storm in Northwest History'". Newsweek. 2021-10-22. Retrieved 2022-11-24.
  28. ^ "Bomb cyclone: What it is, where the term came from and why it's not a hurricane". kgw.com. October 27, 2021. Retrieved 2022-11-24.

External links[edit]

Wikimedia Commons has media related to Severe Tropical Storm Namtheun (2021).
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