|Above: Himawari-8 infrared image of Super Typhoon Wutip taken at 2:10 am EST Monday, February 25, 2019. At the time, Wutip was a Category 5 storm with 160 mph winds--the first Northern Hemisphere Category 5 tropical cyclone on record in February. Image credit: NOAA/RAMMB.|
Super Typhoon Wutip underwent an impressive burst of rapid intensification on Monday morning in the waters about 300 miles west of Guam, topping out as Category 5 super typhoon with a central pressure of 915 mb and sustained winds of 160 mph at 2 am EST. Wutip is the first Category 5 storm ever observed in the Northern Hemisphere in the month of February.
According to NOAA’s Historical Hurricane Tracks database, only seven January and February Category 4 or Category 5 typhoons have been recorded in the Northwest Pacific since records began in the late 1940s. Wutip is tied with Super Typhoon Ophelia of 1958 as the strongest typhoon ever observed these two months. Ophelia peaked as a Category 5 storm with 160 mph winds on January 13, 1958. The previous strongest February typhoon on record was Super Typhoon Higos, which hit 150 mph winds on February 10, 2015.
It is unusual to see a Category 5 storm form with such cool ocean temperatures. According to the 9Z February 25 discussion from the Joint Typhoon Warning Center, sea surface temperatures (SSTs) were a mere 26 - 27°C (79 - 81°F) during Wutip’s rapid intensification to Category 5 strength, and the ocean had a low total heat content. Update: An email I received from hurricane scientist Karl Hoarau detailed an observation from an ocean sensor that measured an ocean temperature of 27.5°C (82°F) on February 19 from the surface to a depth of 75 meters at 13.6°N, 143.3°E, in the region where Wutip intensified. Thus, Wutip's intensification to a Category 5 storm was less improbable than it originally appeared.
Using thermodynamic theory, we can compute a quantity called the maximum potential intensity of a tropical cyclone, based on the prevailing temperatures in the atmosphere and ocean. The maximum potential intensity of Wutip on Monday morning was rated approximately as a high-end Category 4 storm with 150 mph winds, according to an analysis by Dr. Kerry Emanuel (Figure 1). Given that Wutip intensified to be about 5 - 10 mph stronger, this was an impressive feat. Wutip made up for its lack of favorable SSTs with some unusually favorable upper level winds: wind shear was almost non-existent, less than 5 knots, and the typhoon took advantage of two strong upper-level outflow channels, one to the north and one to the south.
|Figure 1. Using thermodynamic theory, we can compute a quantity called the maximum potential intensity of a tropical cyclone, based on the prevailing temperatures in the atmosphere and ocean. The maximum potential intensity (MPI) of Wutip on Monday morning using images provided by wxmap.org was as a high-end Category 3 storm with 125 mph winds and a central pressure of 940 - 945 mb. However, hurricane scientist Kerry Emanuel emailed me to say that tropical cyclones create holes in the analyzed potential intensity owing to their warm cores, so it is probably not a good idea to interpolate MPI maps to estimate PI at actual storm locations. Above is a chart showing the MPI of Wutip over time (orange line), corrected for the storm's warm core. Note that the MPI is meant to apply to the circular wind component, so fast-moving tropical cyclones will be able to achieve higher winds that their MPI might suggest. Image credit: Kerry Emanuel.|
As of 10 am EST Monday, the Joint Typhoon Warning Center had Wutip as a weaker 150 mph Category 4 super typhoon. Satellite images showed that Wutip was likely undergoing an eyewall replacement cycle, and the intensity of the eyewall thunderstorms was waning. Continued weakening is expected as Wutip heads northwest over cooler waters and into an area of increased wind shear. The typhoon is not a threat to any land areas, though it will continue to bring high surf and dangerous rip currents to Guam through Tuesday.
Wutip made its closest pass to Guam on Saturday morning (EST), passing about 180 miles to the island’s southwest. Winds at the Guam Airport peaked at 39 mph--minimal tropical storm force—at 11:54 am Saturday (local time), and gusted as high as 56 mph during the day. The typhoon dumped 8 – 12” of rain over southern Guam, and 4 – 7” over central Guam. Waves near the coast reached 20 feet on Saturday afternoon. Fortunately, the typhoon caused no injuries, major damage, or significant flooding on Guam, according to the Guam Daily Post.