An average of 6 to 7 tropical cyclones hit the Philippines each year. In November 1991, Tropical Storm Thelma became one of the most devastating tropical systems to impact the Philippines in the 20th century.
Thelma began as a tropical disturbance over the Eastern Caroline Islands (Western Pacific region). The system moved west- northwest and was identified as Tropical Depression 27W on November 1, 1991. The storm continued heading west until 4 November, where its track shifted to the west-southwest. At this time, the system was also upgraded to a tropical storm with peak winds reaching approximately 80 km/h (50 mph). Tropical Storm Thelma made landfall on 5 November in the eastern Philippines on the island of Samar. Following landfall, Thelma continued westward with weakening winds of 64 km/h (40 mph). Strong vertical wind shear in the South China Sea kept Thelma from intensifying further. Thelma then passed over the Island of Leyte on 6 November, and on 8 November the storm struck eastern Vietnam. Shortly after this, the system dissipated.
Tropical cyclones that do not attain typhoon (or hurricane) intensity can still be deadly (see Tropical Storm Allison). While Thelma was considered a minimal storm and did not produce the strongest of winds, it did produce torrential rains. An estimated 580.5 millimeters (22.85 inches) of rain fell over the Tongonan Geothermal Site in the Eastern Phillipines. In the 24-hour period it took Thelma to cross the Phillipines, as much as 152.4 millimeters (6 inches) of rain fell over several areas. This rainfall resulted in catastrophic events such as dam failures, landslides, and flash flooding, which in turn, caused an estimated 6,000 casualties. This made Tropical Storm Thelma the deadliest storm of the 1991 Pacific typhoon season. Over half of the deaths were reported in the port city of Ormoc on the Philippine Island of Leyte. Here, a 2.4 m (8 ft) storm surge swept through the area. Three-quarters of the city was destroyed in the subsequent flooding. Additionally, a number of homes were flattened, leaving 20,000 people in Ormoc homeless. Another 30,000 people were homeless throughout the Leyte region leaving a total of 50,000 people homeless following the storm. Total damage from Tropical Storm Thelma in the Philippines and Vietnam, is estimated to have cost $19 million (1991 USD; $30.4 million, 2009 USD).
1991 Annual Tropical Cyclone Repot- Joint Typhoon Warning Center, Guam, Mariana Islands
NOAA Backgrounder- NOAA’s Top Global Weather, Water and
Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA). Climatology and Agrometerology. Important Facts about Tropical Cyclones- Five (5) Most Destructive Typhoon that affected the Philippines, in terms of death.
Divine Wind- Kerry Emanuel (there is a blurb about the storm on page 266)
Joint Typhoon Warning Center. Appendix B: Characteristics of Tropical Cyclones Affecting the Philippine Islands (Shoemaker 1991).
National Institute of Informatics
Wikipedia- 1991 Pacific typhoon season
Wikipedia- Tropical Storm Thelma