Typhoon Olga, known in the Philippines as Typhoon Didang, was a strong typhoon that brought widespread damage to the Philippines in May 1976, causing what was called the "worst flooding in 30 years". The storm killed over 300 people and displaced over 1.3 million others. The storm originated from an area of several surface circulations on May 4, in which the JTWC first noted its predecessor as a southwestward-moving storm on May 12. However, it was first tracked by the JMA on May 11. Nevertheless, it strengthened to a tropical storm while continuing its motion and track. However, it weakened to a tropical depression as it slowly interacted with another circulation to its east, in which the new system dominated over the existing one. The JMA and JTWC still treated the storm as Olga as it entered the area of responsibility of the Philippines, in which the state weather bureau tracked the system as "Didang". Despite the presence of shear around the storm, the system slowly consolidated and grew as it neared the country and few hours prior to landfall, it rapidly intensified to a Category 3 storm before its landfall over Aurora on May 21. Upon inland, Olga subsequently weakened to a tropical storm as it slowed down over Central Luzon before finally exiting through the South China Sea on May 24. There, it slightly strengthened to a tropical storm as it neared land again, this time over Northern Luzon before becoming absorbed by a subtropical disturbance to the south of Okinawa on May 28, in which the JTWC last monitored the system one day prior. However, the JMA continued to track the system along with Olga's remnants until they dropped their advisories while near the International Date Line on May 31.

As a slow-moving system, Olga caused copious amounts of rainfall over the Philippines, with one area recording 50 inches of rain (1,300 mm), becoming one of the wettest tropical cyclones the island nation had ever endured. winds were also recorded at Iba, where sets for the movie Apocalypse Now were destroyed and its staff were forced to shelter in hotels and houses. 374 people were killed and over 1.3 million were left homeless. Many public infrastructures including a dam, dikes and other reservoirs were damaged while agricultural crops were inundated by the storm's rains. Further, floods affected the wide swath of Luzon, with the Central portion of the island being the most affected. Damages from the storm were officially estimated by the President at that time, Ferdinand Marcos to be at $70 million. Meanwhile, its deaths and the resulting destruction resulted in its local name “Didang” being retired.

Meteorological history

On May 4, the JTWC noted multiple surface circulation zones inside a trough near Micronesia. For some of its early life, this precursor circulation generally moved southwestward, although the Japan Meteorological Agency (JMA) first tracked its predecessor at 18:00 UTC of May 11 as a system. On May 12, the JTWC had issued a warning on the system, citing that one circulation had started to overtake the others. Six hours later, the disturbance made a west-northwest movement as being guided by the southern periphery of a subtropical ridge in the Pacific before the agency upgraded the system to a tropical storm on the next day in the afternoon.

That night, satellite imagery revealed the presence of another circulation, located to the east of Olga. The new circulation interacted with the strengthening system, before the original center dissipated and its remaining convection had been absorbed by the second feature while moving west-northwest. Slowly but modest intensification prevailed over the disturbance, and the new cyclone reintensified to a tropical storm. However, both the JMA and JTWC continued tracking this system as Olga. It then inclined northwards due to a shortwave trough trailing across the westerlies on May 16 before resuming its track to the west-northwest as a result of the trough moving to the east. At this time, Olga was now tracked by PAGASA entered the Philippine Area of Responsibility (PAR) and assigned it the local name “Didang”. Olga subsequently entered an area of unfavorable wind shear caused by a 200 mb ridge inclined over the Southeast Asia and despite this, it slowly intensified while nearing the mainland Philippines. The cyclone also initiated a counterclockwise loop and slowed down as a result of a long-wave trough moving off the east coast of China. The system completed this loop on May 20 while continuing to slowly strengthen. Reconnaissance aircraft reports from 03:30 UTC and 19:47 UTC indicated that Olga started to underwent rapid intensification as a pressure drop of 44 mb (from 978 mb to 934 mb) were recorded. At approximately 00:00 UTC of the next day, Olga made landfall on the province of Aurora with an estimated maximum sustained winds of and a barometric pressure of , making at a Category 3 typhoon.

Upon moving inland, Olga's winds rapidly degraded to tropical storm-force winds as it passed over Baler Bay before crossing through Central Luzon. Moving with a forward speed from 2 to 4 knots, it moved to the west-southwest, before taking a westward path. Still as a gale-force system, the cyclone turned northwest before exiting through Lingayen Gulf on May 24. It subsequently reintensified slightly before turning to the northeast, this time sparing Northern Luzon a direct hit again from the system as it passed through Batanes as it inclined north-northeast. By the next day, what was Olga is now just a low-level circulation separated through its convection while accelerating away from the typhoon-stricken Philippines. The system was last tracked by the weather bureau of the Philippines on May 26 before the final advisory was issued by the JTWC at 06:00 UTC of that day while located to the east of Hengchun in Formosa (now Taiwan). The agency also noted that the remnants of Olga were absorbed into a subtropical disturbance on May 27 to the south of Okinawa, although the JMA continued to track the system until they dropped monitoring it on 12:00 UTC of May 31 near the International Date Line.

Effects The Philippines suffered a direct hit from Olga on May 21, when the system made landfall over Aurora. Along with the prevailing southwest monsoon over the country, the cyclone caused heavy rainfall along the Southern, Central and Northern portions of Luzon, causing catastrophic floods. Millions lost their homes due to the inundation and many reservoirs overflowed and burst due to continuous downpour, again affecting many individuals. The final death toll for the storm were at 374 while damages reached in millions of dollars. At Cubi Point, the rainfall exceeded over , which would place the system as one of the wettest tropical cyclones in the Philippines. The summary of the events after the storm wrecked through the country are summarized by date as follows:

May 19 On May 19, before moving inland, Olga's rainbands caused heavy rains, leading to flash floods in metropolitan Manila. 8,000 in Manila were required to leave their homes and thousands of commuters were stranded. In a suburb of Caloocan, seven feet of floodwaters were seen; navy amphibious tanks were sent to evacuate people whose are in their homes to schools for their safety. As a response to this, the Philippine President at that time, Ferdinand Marcos lifted the regular 1-4 am martial law curfew to let thousands of stranded passengers go home without any fines.

May 20 On May 20, seven deaths were further confirmed from the storm. Olga's flooding was also described as the “worst in 30 years”, according to the authorities in the Philippines. At least 10,000 individuals forced to flee their homes in Quezon City due to over of rain, with the said amount being confirmed by Roman L. Kintinar, the chief of the PAGASA. Tens of thousands of motorists and commuters were also stranded in capital Manila. Emergency safety shelters were built in several churches and schools throughout the area for the evacuees while the navy frogmen rescued 71 persons from a flooded residential area in an unknown place outside Manila. Ten persons were reported to have been missing there. Over than 1,500 persons were also trapped and affected by six-feet waters in Mandaluyong. Communications outside the metropolitan area were cut and authorities there said that no reports of damages were received as of that date in provinces that are also affected by Olga. As a result, President Marcos declared Manila and five other Luzon provinces in state of emergency and ordered all businesses in Manila and Quezon City to be closed except the essential operations. Floods came as workers in the city were reportedly finishing 25 inundation-control projects that were set up at that time.The Philippine Red Cross appealed help to USAID and local residents to the area for food supplies for the victims of the storm.

May 21 The death toll further rose to 25 and 8 being missing on May 21. Sixteen of them are recovered from the rising waters on an unknown place in the country. Two light aircraft with 12 persons aboard are missing during the onslaught of the typhoon. The proclaimed state of calamity in Manila and nearby areas froze food prices and imposed penalties in hoarders and profiteers there. President Marcos also ordered the Philippine Air Force to run cloud-seeding operations in the mountainous areas north of the capital to induce rainfall away from its storm clouds to populous areas. Marcos said in news reports from the Philippines that a PAF C-47 aircraft poured sodium chloride onto Olga to contain the record rainfall it brought onto the country's capital, but it did still dropped record-heavy downpour. It is based on meeting with relief and rescue officials that Marcos did the decision to declare a state of calamity in several areas in the Philippines that are severely affected from the storm. Storm signals were continued to be raised and maintained as Olga emerges onto the South China Sea.

May 22 A plane of 5 people crashed in a wooded hills 40 miles to the south of Manila from Leyte to the area. The death toll at that date were set at 35. PRC noted that reports from different provinces that are also hit hard by Olga were delayed due to broken power lines. A rescue official also informed the media in the country that bad weather also prevented the dispatch of planes to check the Seng Hong, a Panamanian-registered freighter that was reported to be run aground near Mamburao Bay, located to the south of the capital. 18 passengers were on board. The other aircraft, a Philippine navy plane that was bound for Manila from Palawan with seven passengers that was also affected by Olga.

May 24