Super Typhoon Haiyan — which is one of the strongest storms in world history based on maximum windspeed — is about to plow through the Central Philippines, producing a potentially deadly storm surge and dumping heavy rainfall that could cause widespread flooding. The densely populated city of Manila, home to 12 million, is in the storm's path, although it is predicted to escape the worst of the winds and storm surge. As of Thursday afternoon Eastern time, Haiyan, known in the Philippines as Super Typhoon Yolanda, had estimated maximum sustained winds of 195 mph with gusts above 220 mph, which puts the storm in extraordinarily rare territory. Since 1969, only three storms have had sustained winds close to this magnitude — Hurricane Camille in 1969, Super Typhoon Tip in 1979, and Hurricane Allen in 1980. No storm in the Atlantic has ever been stronger than Haiyan, accoring to The Weather Channel. Haiyan is capable of causing catastrophic damage in the central Philippines and its outer bands are already starting to affect the island nation. The U.S. Navy's Joint Typhoon Warning Center forecasts that Haiyan will cross the Central Philippines as a Category 4 or 5 Super Typhoon, and then re-emerge over open water, before making landfall in Vietnam as a Category 3 typhoon on November 10. Ryan Maue, a meteorologist at WeatherBELL Analytics, said that Haiyan appears to be the strongest storm since Super Typhoon Tip in 1979. Maue said the storm has avoided the typical hiccups that other intense storms encounter, such as eyewall replacement cycles, during which a storm's inner core undergoes a reorganization. Such cycles can cause a Category 5 storm to weaken to a Category 3 or 4 storm, before re-strengthening. Instead of doing this, though, Haiyan has remained at peak strength for more than 24 hours, which is unusual, and even strengthened on Monday morning. After hitting the Leyte province, the Philippines' Department of Science and Technology expects the storm to traverse the central Philippines from Biliran to Busuanga before passing into the West Philippine Sea. The Department is warning coastal residents to expect storm surges "which may reach up to 7-meter (23 feet) wave height," along with flooding and mudslides. The storm poses an especially grave danger to the capital of Leyte, the city of Tacloban, which has about 220,000 people and lies along or just to the north of the storm's path where the most intense winds and storm surge will come ashore. For the past 24 hours, the storm has remained at a strength close to the theoretical upper limit that cyclones can reach. Unlike in the tropical North Atlantic, there is no aircraft reconnaissance of tropical storms and typhoons in the Western Pacific, so the actual wind speeds and minimum central air pressure — two key parameters used to classify such storms — are being estimated using satellites. Storm surge forecasts from the Philippines' Project NOAH indicate a maximum storm tide (storm surge plus the tide level) of 16.4 feet at Ormoc in Leyte Province on November 8, with 14-16 foot storm tides occurring in the provinces of Palawan, Quezon, Biliran, and others. The storm tide forecast for Manila is 5 feet, but the city is so low-lying that flooding may still occur there. Sea level rise from global warming is escalating the risk posed by storm surges across the globe, including in low-lying areas of the Philippines. Aiding the storm's development has been a plentiful supply of warm ocean waters, low atmospheric wind shear and plentiful amounts of warm, moist air surrounding the storm. Chia-Ying Lee, a researcher at Columbia University's International Research Institute for Climate and Society, told Climate Central in an email that Haiyan's moderate forward speed has prevented it from encountering the cooler ocean waters that its potent winds are stirring up from deep below the ocean's surface, which would have weakened the storm. Lee said there have been 9 years that have had more than three super typhoons in the Western Pacific Ocean (equivalent to Category 4 and 5 hurricanes) for the period from 2002-2012. "So actually, having 3 or more super typhoons is quite common, at least in the last decade." Lee said that Haiyan is unique in that it reached Category 5 strength at a very southern latitude, although it did not set a record for this. ". . . In general, a storm's movement has a northward component, (so) the longer it takes for the storm to reach Category 4 or 5, the further north it gets. For Haiyan, it went through a rapid intensification process and has not actually experienced any weakening stage, while lots of storms experienced ups and downs before reaching such a strong stage," she said. The Western Pacific Ocean Basin has been far more active than the Atlantic Hurricane Season this year. Haiyan is the fourth Category 5 storm in the Western Pacific this year. There was also a Category 5 storm in the Eastern Pacific this year.

• published: 08 Nov 2013
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