image: NASA's Aqua satellite and RapidScat instrument showed that Guillermo was getting better organized and strengthening. On July 31, Guillermo became the fifth of the Eastern North Pacific 2015 hurricane season.
On July 30, the RapidScat instrument that flies aboard the International Space Station measured the storm's surface winds when it was still a tropical storm. When RapidScat gathered data on the Guillermo, the strongest winds were on the eastern side of the storm, and measured about 24 meters per second (53.6 mph/ 86.4 kph). Those winds continued to increase as the storm became more organized.
Later in the day, NASA's Aqua satellite passed over Guillermo as it continued moving west through the Eastern Pacific Ocean. The Moderate Imaging Spectroradiometer (MODIS) instrument aboard Aqua captured a visible-light image on July 30, 2015 at 21:55 UTC (5:55 p.m. EDT).
Forecaster Pasch at the National Hurricane Center noted that imagery showed Guillermo's cloud pattern continued to become better organized (over the previous day), with well-defined convective banding (of thunderstorms) and a fairly symmetric upper-level outflow pattern. A recent microwave image from the Global Precipitation Measurement (GPM) microwave imager showed a nearly closed low-level eyewall.
At 5 a.m. EDT (0900 UTC) on July 31, satellite images indicated that the maximum sustained winds have increased to near 80 mph (130 km/h) with higher gusts. The center of Hurricane Guillermo was located near latitude 11.5 North and longitude 130.6 West, about 1,526 nautical miles east-southeast of Hilo, Hawaii. Guillermo was moving toward the west-northwest near 16 mph (26 kph), and this general motion is expected to continue through Saturday. The estimated minimum central pressure is 985 millibars.
The hurricane-force winds cover a small area, and extend outward up to 25 miles (35 km) from the center. Tropical storm force winds extend outward up to 115 miles (185 km) from the center.
Pasch noted that Guillermo should be moving over warm waters, and in a moist mid-level environment with moderate vertical wind shear allowing further strengthening over the next couple of days.
Credit: Image: NASA JPL, Doug Tyler Text: NASA Goddard, Rob Gutro