Category 3 Typhoon Hagupit Threatening Philippine Islands Hit by Haiyan

By: Dr. Jeff Masters , 4:22PM,GMT on December 3,2014

Category 3 Typhoon Hagupit put on a respectable burst of rapid intensification over the past day, and is steaming west-northwest at 21 mph towards the same portion of the Philippine Islands devastated by Super Typhoon Haiyan in November 2013. Hagupit is over very warm ocean waters of 30°C (86°F) and is under light wind shear around 10 knots--conditions which favor intensification into a 150-mph super typhoon by Thursday. The ridge of high pressure steering Hagupit will weaken late this week, putting the typhoon into a region of weak steering currents, making the threat to the Philippines uncertain. The storm will slow down and potentially turn north, keeping the core of the typhoon well out to sea, as predicted by this morning's 00Z and 06Z runs of the GFS model. Most concerning are the recent runs of the usually-reliable European model, which has been consistently showing a landfall near 18 UTC Saturday very close to Tacloban on Leyte Island, which endured the brunt of Super Typhoon Haiyan's fury. However, if Hagupit does hit the Philippines, it will be a much weaker storm than Haiyan was. There is less heat energy available in the ocean for Hagupit, and wind shear is expected to rise to the high range on Friday as strong upper-level winds tear at the storm. Heavy rains, not high winds and storm storm surge, will likely be the greatest threat for the Philippines from Hagupit.


Figure 1. MODIS satellite image of Typhoon Hagupit at 04:30 UTC on Wednesday December 3, 2014. At the time, Hagupit was a Category 3 storm with 115 mph winds. Image credit: NASA.

Less ocean heat energy available to Hagupit compared to Haiyan
As I discussed in my November 13, 2013 post, Super Typhoon Haiyan's Intensification and Unusually Warm Sub-Surface Waters, when Super Typhoon Haiyan exploded into one of the most powerful storms ever recorded on Earth, the mighty storm took advantage of some unusually warm sub-surface waters. Haiyan intensified into a Category 5 super typhoon with 195 mph sustained winds, as rated by the Joint Typhoon Warning Center on November 7, 2013. Haiyan tracked over surface waters that were of near-average warmth, 29.5 - 30.5°C (85 - 87°F), but the waters at a depth of 100 meters (328 feet) beneath Haiyan during its rapid intensification phase were a huge 3°C above average, according to Professor I-I Lin of the Department of Atmospheric Science at the National Taiwan University. The sub-surface waters east of the Philippines have warmed dramatically over the past twenty years. According to Pun et al. (2013), "Recent increase in high tropical cyclone heat potential area in the Western North Pacific Ocean", the depth to where ocean temperatures of at least 26°C (79°F) penetrates has increased by 17% since the early 1990s, and the Tropical Cyclone Heat Potential has increased by 13%. The warm-up is due to an increase in the surface winds blowing across the region--the trade winds--which have caused a southward migration and strengthening of the North Equatorial Current (NEC) and the North Equatorial Counter Current (NECC). However, during the past few months, the trade winds have weakened in the Western Pacific, as the ocean has moved towards an El Niño-like state (as of this week, ocean temperatures in the Eastern Pacific had reached the threshold of "moderate" El Niño conditions.) Weaker east-to-west blowing surface winds means that warm water in the Western Pacific can slosh eastwards towards South America, resulting in a weaker North Equatorial Current in the waters east of the Philippines, and less warm water and heat energy to fuel typhoons threatening those islands.


Figure 2. Ocean temperatures at a depth of 100 meters (328 feet) on December 1, 2013 (top), shortly after the passage of Super Typhoon Haiyan, and on December 1, 2014 (bottom.) Note how weaker east-to-west trade winds near the surface in 2014 have led to a weaker North Equatorial Current, resulting in much cooler waters to the east of the Philippines compared to in 2013. Image credit: Japan Meteorological Agency.

Jeff Masters