Tropical Depression Usman

Tropical Depression Usman was a weak but deadly tropical cyclone that impacted the southern Philippines in December 2018. Tropical Depression Usman originated first as a low-pressure area to the east of Palau on December 23. Slowly intensifying, the system became a tropical depression two days later. The system maintained its intensity while moving in a general west-northwestward direction approaching the eastern portion of the Philippine islands. However, due to unfavorable conditions, the depression weakened into a remnant low on December 29, while making landfall over Eastern Samar thereafter.

Tropical Depression 35W (Usman)
Tropical depression (JMA scale)
Tropical depression (SSHWS)
Tropical Depression Usman over the Philippines on December 29
FormedDecember 25, 2018
DissipatedDecember 29, 2018
Highest winds10-minute sustained: 55 km/h (35 mph)
1-minute sustained: 55 km/h (35 mph)
Lowest pressure1000 hPa (mbar); 29.53 inHg
Fatalities156 total, 26 missing
Damage$103 million (2018 USD)
Areas affectedCaroline Islands, Philippines
Part of the 2018 Pacific typhoon season

While the system possessed weaker winds, it brought torrential rainfall over much of Visayas, hitting the regions of Eastern Visayas and Bicol the hardest. Sea travel to the country was vastly disrupted during the holiday season. Torrential rain caused flooding to as high as 7 feet in Northern Samar. An estimated of 36,000 houses were damaged due to Usman. A total of 156 people perished during storm, while 26 people remain missing. Damage from Usman is estimated to be about ₱5.41 billion (US$103 million). After the season, the PAGASA struck off the name Usman from their naming lists because it exceeded more than ₱1 billion worth of damages.

Meteorological history

Map plotting the storm's track and intensity, according to the Saffir–Simpson scale
Map key
  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
Extratropical cyclone / Remnant low / Tropical disturbance / Monsoon depression

On December 23, the Joint Typhoon Warning Center (JTWC) began monitoring a tropical disturbance that had developed about 657 km (409 mi) to the east of Palau.[1] Around that time, the system was located in an area of moderate vertical wind shear and warm 28–30 °C (82.4–86 °F) sea-surface temperatures.[1] The disturbance slowly intensified and the JTWC issued a tropical cyclone formation alert at about 09:00 UTC on December 24.[2] At that time, the convection, or thunderstorm activity, around the system's low-level circulation center was rather sheared. Dvorak estimates were around T1.5 at the time, signalling that the system had 1-minute sustained winds of 45 km/h (30 mph).[3] This prompted the JTWC to upgrade the disturbance to a tropical depression, with the system receiving the designation 35W.[4] By 21:00 UTC of the same day, visible satellite imagery showed shallow rain banding (which is a cloud structure that is associated with an area of rain and thunderstorms) wrapping into a tight, but exposed center, with poorly organised convection.[5] The Japan Meteorological Agency (JMA) declared the system to be a weak tropical depression at around 06:00 UTC of December 25.[6] Around the same time, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) had reported that the depression had entered their area of responsibility and assigned the local name Usman.[7]

The JMA began issuing advisories on 12:00 UTC of December 25, when they considered that the tropical depression had 10-minute sustained winds of 55 km/h (35 mph).[8] With Usman's ragged center, the system remained disorganised, as wind shear was becoming displaced to the northwest.[9] By 03:00 UTC on December 26, satellite imagery depicted that the system had multiple, minor circulation centers revolving around its original center. The storm's structure became somewhat disorganised due to the lack of convection, being blown off by the southeasterly wind shear.[10] The system maintained its intensity until the next day, when satellite imagery showed a broad circulation with excellent outflow along with extensive deep convection flaring near its center. At this point, both the JMA and the JTWC predicted that the system would intensify into a tropical storm within the next 24 hours.[11][12] Thereafter, convection had increased around the system, and the system's center became much more organised.[13] At 00:00 UTC on December 28, the JTWC reported that the system's 1-minute sustained winds to 55 km/h (35 mph).[14] A cold cold cover began obscuring the system's elongated center, thereafter.[15] On December 29, the system's central cold cover began to dissipate, and the JTWC had stated that the system began weakening and deteriorating.[16] Tropical Depression Usman made landfall in Borongan, Eastern Samar on 06:00 UTC of the same day, as the PAGASA downgraded the system to a low-pressure area.[17] The JMA stated that the system was located in an area of increasing wind shear.[18] Several hours later, both the JMA and the JTWC issued their final advisory on the system.[19][20]

Preparations and impact

On December 27, as Tropical Depression Usman inches closer to the eastern portion of the Philippines, the PAGASA raised a Tropical Cyclone Warning Signal #1 over much of the Bicol region and the Eastern Visayas region, with some even extending as north as Quezon province and as west as Cebu.[21] Local officials advised residents at that time to take precautionary measures in areas of low-lying and mountainous areas, especially those living near river channels.[22] The PAGASA also warned on sea travel, either to fishermen or those with small sea crafts, are risky in the seaboards of Southern Luzon, Central Luzon and the Surigao provinces due to rough seas combined with the northeast monsoon.[21][23] Heavy rains that could trigger landslides and flashfloods were expected in the areas under the alert signals.[21] Roughly 1,000 passengers later became stranded in Bacolod after sea travel was suspended.[24] The region of Western Visayas, which includes the island of Palawan, was raised a TCWS #1 on December 28,[25] as 851 passengers were stranded in that region alone.[26] As of 5 p.m. local time, the NDRRMC raised the "blue alert" status in much of the Western Visayas region, meaning that 50 percent of the RDRRMC personnel are on standby for emergencies and it is the second highest alert level.[26] At this point, the number of passengers stranded from the cause of suspended sea travel rose to 13,000,[25] where 6,000 of them were from the Bicol Region.[27] In the city of Tacloban, their mayor ordered to suspend work in government offices and their local officials have set up 71 evacuation centres ready for displaced families.[28]

Following the landfall and the deterioration of the tropical depression, widespread flooding and landslides were reported in many areas. Six towns in Masbate saw 61 families, or 259 individuals forced to evacuate their homes due to extreme flooding.[29] Local officials in the area also lifted the temporary ban for sea travel on the morning of December 29 to allow the remaining stranded passengers to travel.[29] This was the same in the Bicol Region were 3,900 people were evacuated. In Northern Samar, the heavy rained caused flooding to as high as 2–7 ft (24-84 inches).[30] In Bicol, 473.1 mm (18.6 in) of rain was recorded for the two days of December 28 and 29.[31] Strong winds and heavy rain from Usman caused the shutdown of some power plants, which led to power outages in some areas In Albay, Catanduanes and Eastern Visayas.[30] On December 30, a state of calamity was raised in the provinces of Camarines Sur, Camarines Norte and Sorsogon, along with the municipality of Polangui in Albay.[32][33] Eight other municipalities in Oriental Mindoro were also raised a state of calamity by local officials on the next day.[32]

Throughout the country, a total of 238,127 families were affected by Usman. About 36,574 houses were either partially or totally damaged.[34] A total of 156 people have died from the storm, with 105 people being injured. 26 people have remained missing. An estimated cost of damages were toppled to ₱5.41 billion (US$103 million), where ₱1.95 billion (US$37.1 million) were to be part of agricultural damages and ₱3.46 billion (US$65.9 million) were to be part of infrastructure damages.[34]

Aftermath and retirement

In January 2019, Mahar Lagmay, a Disaster scientist, claimed that the high death toll by the system was caused by the PAGASA issuing incorrect and misleading forecasts for Tropical Depression Usman.[35][36] The PAGASA then responded to the scientist's statement regarding this claim, and stated that Lagmay had used the "hour rainfall intensity" classification instead of the "24-hour accumulated rainfall" classification, where it has been used commonly in their tropical cyclone bulletins.[35] Local officials also criticised the PAGASA due to the fact how their residents became confused and complacent when Usman was downgraded to a low-pressure area, which also meant the PAGASA lifting any storm signals.[35] The PAGASA later addressed and confirmed this, however they explained that the storm signals are distinct from the amount of rainfall accumulated, as the signals described more of the expected winds in the area.[35] They also added that they did release a weather advisory on the low-pressure area (that was once Usman) on December 29 regarding that "moderate to heavy rains will continue over Bicol Region in the next 24 hours."[35]

Because the system caused damages of over ₱1 billion, the PAGASA retired the name Usman, despite it being used for the first time in their naming lists. In March 2019, the PAGASA revised their lists and replaced the name with Umberto for the 2022 season.[37]

See also

References

  1. "Significant Tropical Weather Advisory for the Western and South Pacific Oceans 1630Z 23 December 2018". Joint Typhoon Warning Center. December 23, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  2. "WTPN21 PGTW 240900". Joint Typhoon Warning Center. December 24, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  3. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 01". Joint Typhoon Warning Center. December 24, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  4. "Tropical Depression 35W (Thirty-five) Warning Nr 001". Joint Typhoon Warning Center. December 24, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  5. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 02". Joint Typhoon Warning Center. December 24, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  6. "Archived copy". Archived from the original on 2018-12-26. Retrieved 2018-12-26.{{cite web}}: CS1 maint: archived copy as title (link)
  7. "Tropical depression Usman enters PAR; landfall seen on Friday". ABS-CBN News. ABS CBN News. December 25, 2018. Archived from the original on February 3, 2020. Retrieved May 25, 2020.
  8. "RSMC Tropical Cyclone Advisory TD". Japan Meteorological Agency. December 25, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  9. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 05". Joint Typhoon Warning Center. December 25, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  10. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 07". Joint Typhoon Warning Center. December 26, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  11. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 11". Joint Typhoon Warning Center. December 27, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  12. "Archived copy". Archived from the original on 2018-12-27. Retrieved 2018-12-27.{{cite web}}: CS1 maint: archived copy as title (link)
  13. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 13". Joint Typhoon Warning Center. December 27, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  14. "Tropical Depression 35W (Thirty-five) Warning Nr 015". Joint Typhoon Warning Center. December 28, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  15. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 15". Joint Typhoon Warning Center. December 28, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  16. "Prognostic Reasoning for Tropical Depression 35W (Thirty-five) Warning Nr 20". Joint Typhoon Warning Center. December 29, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  17. "Usman makes landfall in Eastern Samar, weakens into LPA". Rappler. December 29, 2018. Archived from the original on October 3, 2019. Retrieved May 25, 2020.
  18. "Archived copy". Archived from the original on 2018-12-29. Retrieved 2018-12-29.{{cite web}}: CS1 maint: archived copy as title (link)
  19. "Tropical Depression 35W (Thirty-five) Warning Nr 021". Joint Typhoon Warning Center. December 29, 2018. Archived from the original on August 22, 2020. Retrieved May 25, 2020.
  20. "Archived copy". Archived from the original on 2018-12-29. Retrieved 2018-12-29.{{cite web}}: CS1 maint: archived copy as title (link)
  21. "20 areas under Signal No. 1 due to Tropical Depression Usman". Rappler. December 27, 2018. Archived from the original on December 27, 2018. Retrieved May 25, 2020.
  22. "'Usman' intensifies; Eastern Visayas, Caraga at risk". SunStar. December 26, 2018. Archived from the original on December 26, 2018. Retrieved May 25, 2020.
  23. "Signal No. 1 raised in 11 areas due to 'Usman'". Philippine Daily Inquirer. December 27, 2018. Archived from the original on June 11, 2019. Retrieved May 25, 2020.
  24. Erwin Necavera (December 27, 2018). "At least 1,000 passengers stranded in Bacolod due to TD Usman". Philippine News Agency. Archived from the original on March 5, 2019. Retrieved May 25, 2020.
  25. "Signal no. 1 up in several areas as Usman nears Eastern Samar". ABS-CBN News. ABS CBN News. December 28, 2018. Archived from the original on February 3, 2020. Retrieved May 25, 2020.
  26. Cindy Ferrer (December 28, 2018). "'Usman' grounds 851 passengers in Western Visayas". Philippine News Agency. Archived from the original on December 29, 2018. Retrieved May 25, 2020.
  27. Mar Serrano (December 28, 2018). "Nearly 6K passengers stranded in Bicol ports". Philippine News Agency. Archived from the original on January 2, 2019. Retrieved May 25, 2020.
  28. Jazmin Bonifacio (December 28, 2018). "71 evacuation centers ready for displaced families in Tacloban City". Rappler. Archived from the original on December 28, 2018. Retrieved May 25, 2020.
  29. "'Usman' death toll rises to 16 in Bicol". Philippine Daily Inquirer. December 30, 2018. Archived from the original on December 30, 2018. Retrieved May 25, 2020.
  30. "Heavy rain from Usman leaves 3 dead". The Philippine Star. December 30, 2018. Archived from the original on January 1, 2019. Retrieved May 25, 2020.
  31. "Bicol execs blame climate change for 'Usman' deaths: Iba ang lakas ng ulan!". Politikol Bicol. December 31, 2018. Archived from the original on January 7, 2019. Retrieved May 26, 2020.
  32. "1 killed, 2 missing as Oriental Mindoro places 8 areas under state of calamity". GMA News. GMA News. December 31, 2018. Archived from the original on February 20, 2019. Retrieved May 26, 2020.
  33. "3 Bicol provinces under state of calamity due to Usman". Rappler. December 31, 2018. Archived from the original on October 4, 2019. Retrieved May 26, 2020.
  34. Sitrep No.26 re Preparedness Measures and Effects of TD USMAN (PDF) (Report). NDRRMC. January 20, 2019. Archived (PDF) from the original on August 22, 2020. Retrieved January 20, 2019.
  35. "PAGASA: No wrong forecast for Tropical Depression Usman". Rappler. January 16, 2019. Archived from the original on October 23, 2019. Retrieved May 26, 2020.
  36. Mavin Conde (January 8, 2019). "Wrong forecast worsened Usman death toll in Bicol – expert". Rappler. Archived from the original on October 22, 2019. Retrieved May 26, 2020.
  37. "Pagasa 'retires' 3 typhoon names". Manila Standard. March 2, 2019. Archived from the original on March 3, 2019. Retrieved May 25, 2020.
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