The 1991 Pacific typhoon season was a slightly above-average season with 29 tropical storms, 17 typhoons and five super typhoons forming. It was quite a catastrophic season – Typhoon Yunya impacted the Philippines in mid June while in the same time experiencing a volcanic eruption, Typhoon Mireille severely impacting Japan, which became known for being the costliest typhoon on record until it was surpassed by Typhoon Doksuri in 2023, and Tropical Storm Thelma on November which became one of the deadliest storms to strike the Philippines, killing at least over 5,000 people. The season was deadliest since 1975.

It ran year-round in 1991, although most tropical cyclones tended to form in the northwestern Pacific Ocean between May and November 1991. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean. However, the first named storm, Sharon, did not develop until. March 8. The last named storm, Zelda, dissipated on December 5.

The scope of this article is limited to the Pacific Ocean, north of the equator and west of the International Date Line. Storms that form east of the date line and north of the equator are called hurricanes; see 1991 Pacific hurricane season. Tropical Storms formed in the entire west pacific basin were assigned a name by the Joint Typhoon Warning Center. Tropical depressions in this basin have the "W" suffix added to their number. Tropical depressions that enter or form in the Philippine area of responsibility are assigned a name by the Philippine Atmospheric, Geophysical and Astronomical Services Administration or PAGASA. This can often result in the same storm having two names.

Season summary

Systems 32 tropical cyclones formed this year in the Western Pacific, of which 30 became tropical storms. 17 storms reached typhoon intensity, of which 5 reached super typhoon strength.

Severe Tropical Storm Sharon (Auring)

Severe Tropical Storm Sharon existed between March 5 and March 16, 1991. Sharon hit the Philippines.

Typhoon Tim

On March 17, a cluster of thunderstorms grouped together which formed a low pressure area far east of the Mariana islands. The low pressure area rapidly intensified and became a tropical storm 4 days after formation. Favorable conditions allowed the system to continue to intensify into a Category 1 typhoon. High wind shear on March 25 caused the system to weakened, and it transitioned into an extratropical cyclone.

Tropical Storm Vanessa (Bebeng)

Vanessa deepened over the South China Sea.

Typhoon Walt (Karing)

On May 3 an area of disturbed area formed south east of the Mariana Islands. A day later the system strengthened into a tropical depression, and continued to intensify into typhoon status four days later. The system showed annular characteristics on May 11, showing an axisymmetric shape. Walt reached peak intensity on May 12, before showing a distinct eyewall replacement cycle lasting four hours from late May 13 to May 14. When the eyewall replacement cycle was over, a new, larger eye measuring 65 kilometers across formed. Walt soon turned north east, becoming extratropical on May 17, before merging with another extratropical cyclone north east of Japan.

Typhoon Yunya (Diding)

After a month without any activity in the Western Pacific, a weak tropical depression (with winds of only 10 knots) developed just east of the Philippines and south of the Tropical Upper Tropospheric Trough on June 11. Located in an area of little wind shear, it headed southwestward, developing spiral-band outflow and becoming a tropical storm on the 12th. As a small central dense overcast (CDO) developed over Yunya, it rapidly developed, becoming a typhoon on the 13th as it paralleled the eastern Philippines. The mid-level ridge forced Yunya westward, where it briefly reached a peak intensity of winds on the 14th. Subsequently, the eastward building of the subtropical ridge produced unfavorable vertical wind shear that weakened Yunya to a minimal typhoon before hitting Dingalan, Luzon early on the 15th. Yunya left Luzon as a minimal tropical storm at Lingayen Gulf. It turned northward due to a break in the ridge, and dissipated on the 17th near southern Taiwan due to the vertical shear.

Yunya would likely have been an uneventful cyclone had it not struck Luzon on the same day as the climactic eruption of Mount Pinatubo. The ash cloud that normally would have been dispersed across the oceans was redistributed over Luzon by the cyclonic winds of the typhoon, greatly exacerbating the damage caused by the eruption. The water-laden ash fell over the evacuated Clark Air Base, as well as the rest of Luzon, resulting in downed power lines and the collapse of flat-roofed buildings. In some areas it was practically raining mud.

Yunya exited Luzon through Lingayen Gulf as a weak tropical storm and then turned north toward a break in the subtropical ridge. The system continued to weaken due to the strong vertical wind shear. It then brushed the southern coast of Taiwan as a tropical depression and finally dissipated before it could complete full recurvature into the mid-latitude westerlies. Yunya directly caused one death from the flooding and heavy rainfall it left.Joint Typhoon Warning Center. Typhoon Yunya. Retrieved on January 10, 2006.

Typhoon Zeke (Etang)

At least 23 people were killed by Zeke on Hainan Island.

Typhoon Amy (Gening)

145 mph Typhoon Amy, having developed on July 12 over the open Western Pacific, brushed southern Taiwan on the 18th. Its outflow became restricted, and Amy hit southern China on the 19th as a 120 mph typhoon. It caused heavy flooding, resulting in 99 casualties, 5000 people injured, and 15,000 people homeless. In addition, Amy caused the sinking of the freighter in a river, resulting in an additional 31 deaths.

Severe Tropical Storm Brendan (Helming)

Brendan was the third consecutive tropical cyclone to strike China during the month of July.

Typhoon Caitlin (Ising)

Typhoon Caitlin developed from a disturbance in the eastern Caroline Islands. A tropical depression formed on July 23 as the system moved towards the northwest. Tropical Storm Caitlin was named on the 24th and was upgraded to a typhoon the next day. Typhoon Caitlin though several hundred miles away increased the monsoonal flow over the Philippines. Heavy rains caused landslides in the Mt. Pinatubo region killing 16 people. As Caitlin turned to the north the storm passed to the west of Kadena AB, Okinawa at peak intensity of 110 mph. The heavy rains from Caitlin helped to relieve the ongoing drought on the island, one death was reported. Typhoon Caitlin then began to accelerate northwards and passed through the Korea Strait before turning extratropical in the Sea of Japan. Heavy flooding in South Korea killed 2 people and caused $4 million in damage.Joint Typhoon Warning Center. Retrieved on December 26, 2007.

Tropical Depression Enrique

Tropical Storm Enrique formed in the eastern Pacific basin, where it reached its peak intensity as a category 1 Hurricane, becoming Hurricane Enrique. Enrique lasted for several days drifting north of the Hawaiian Islands as a weak system. As Enrique approached the International Dateline, the system started to redevelop. Shortly after crossing the dateline, Enrique became a tropical storm again on August 1. It lasted for less than 24 hours before strong upper-level wind shear dissipated its convection, exposing the cyclone's circulation. No damages or casualties were caused by Enrique. It is one of only eight tropical cyclones to exist in all three tropical cyclone basins in the Pacific Ocean. The others are 1986's Georgette, 1994's Li and John, 1999's Dora, 2014's Genevieve, 2018's Hector and 2023's Dora.

Tropical Depression Doug

Doug was a tropical storm according to the JTWC.

Typhoon Ellie (Mameng)

Ellie was an unusually small typhoon which hit Taiwan as a tropical storm.

Typhoon Fred (Luding)

Typhoon Fred organized from a monsoon trough situated to the east of the Central Philippines, a depression formed on August 11. The depression moved across northern Luzon Island, upon entering the South China Sea the depression was upgraded to Tropical Storm Fred. Fred reached typhoon intensity on August 14 as the storm moved south of Hong Kong. Fred reached peak intensity of shortly before moving across Hainan Island. Fred then turned to the southwest across the Gulf of Tonkin and made a final landfall in northern Vietnam before dissipating. The observed minimum atmospheric pressure value in Kỳ Anh (Hà Tĩnh) during the storm reached 976.9 hPa. As Fred moved south of Hong Kong the oil rig support barge DB29 sank with 195 people on board; 22 people on board the ship were killed. In Guangdong, 90,000 homes were damaged and 9,400 homes were destroyed. Losses in Hong Kong reached 350 million RMB (US$64.8 million). On Hainan Island heavy flooding and landslides from Fred's rains killed 16 people.Joint Typhoon Warning Center. Retrieved on December 26, 2007. Losses on Hainan Island reached 304 million RMB (US$56.3 million). Tropical storm Fred left 5 people dead and 16 injured in Vietnam.

Tropical Depression 13W

13W lasted two days.

Severe Tropical Storm Gladys

Minimal typhoon Gladys brushed by southern Japan on August 22. It moved to the northwest, and hit the Korean Peninsula on the 23rd. It caused more than 20 million yen of damage in Japan, more than 270 million won of damage in South Korea, and in South Korea, it left 103 dead or missing and more than 20,000 homeless.

Tropical Storm 15W

15W was a long-lived depression that moved northwest.

Tropical Storm Harry

Harry originally formed from a small cluster of thunderstorms in mid August.it moved over the Pacific Ocean and became better organized. On August 29, it was given the name “Harry”. It then moved north and made landfall on Japan a few days later. Harry then weakened because of the land and also because when it moved out to sea again, it moved over colder waters and dissipated on August 31.

Typhoon Ivy

Typhoon Ivy formed from a broad monsoon trough situated near Kosrae in the eastern Caroline Islands. A tropical depression formed on September 2 as the system moved towards the northwest, the next day the depression strengthened into Tropical Storm Ivy. Ivy began to rapidly intensify and reached typhoon strength as the storm passed east of Tinian and Saipan in the Northern Mariana Islands. On Saipan one drowning death was reported, but only minor damage was reported in the Northern Marianas. Typhoon Ivy continued on a northwesterly path and reached peak strength of on September 7 prior to recurving to the northeast. Ivy paralleled the southeastern Japan coastline and turned extratropical to the east of Tokyo. As Typhoon Ivy made its closest approach to Honshū, Tokyo and surrounding areas were buffeted by high winds and heavy rains. Over 200 landslides were reported and one person was killed with 4 others missing. Joint Typhoon Warning Center. Retrieved on December 27, 2007. Losses totaled to ¥1.6 billion (US$12 million).

Tropical Storm Joel

Joel hit southern China. Joel killed five people and injured 75 people. 8,680 homes were flooded and 4,000 homes were destroyed. 78,000 hectares of farmland were affected. 130 bridges, 257 irrigation facilities and 70 hectares of fish ponds were damaged. Economic losses reached 400 million RMB (US$74.1 million).

Typhoon Kinna (Neneng)