At 28,000 feet over Tropical Storm Guillermo a bang is heard within the Hurricane Hunters’ WC-130J. ADVERTISING At 28,000 feet over Tropical Storm Guillermo a bang is heard within the Hurricane Hunters’ WC-130J. On most flights, such a sound might
At 28,000 feet over Tropical Storm Guillermo a bang is heard within the Hurricane Hunters’ WC-130J.
On most flights, such a sound might spur concern for the average passenger, but on this flight of the 53rd Weather Reconnaissance Squadron the sound signals the beginning of data collection that will assist Central Pacific Hurricane Center forecasters in narrowing the cone of uncertainty as Guillermo approaches the Hawaiian Islands.
Falling at a rate of 2,500 feet a minute, the dropsonde — a Pringles can-sized contraption that has some resemblance to a used roll of paper towels — makes its way through Guillermo down to the ocean surface. On its 10-minute solo mission, the highly sophisticated device collects an array of data, including wind speed and direction, temperature, humidity and barometric pressure before it hits water.
In all, 17 dropsondes were ejected from the WC-130J late Monday and early Tuesday amid four alpha patterns that took the U.S. Air Force Reserve aircraft through the center of the storm to as low as 5,000 feet above sea level.
All that data streaming in every half-second helps Central Pacific Hurricane Center forecasters more accurately predict not only the potential track for a tropical cyclone, but also its strength and structure, says crew member Nathan Calloway, who is operating the dropsonde tubes.
“We’re like a test tube in a lab,” Calloway says, raising his voice just enough to be heard over the roar of the WC-130J’s engines. “We’re collecting tons and tons of data that satellites just can’t pick up. All they (forecasters) see is the top of the storm (using satellite), we fly underneath the storm, 5,000 to 10,000 feet at times.”
The missions also can result in savings to taxpayers because the cone of uncertainty for the forecast track can be narrowed, prompting fewer evacuations, he adds.
“Evacuating one coastal mile costs about $1 million,” Calloway said, explaining that narrowing the forecast for Hawaii could mean one island needs to evacuate while another does not.
On this nighttime flight — the fourth the crew has taken through Guillermo since arriving from Biloxi, Miss., Saturday — Guillermo shows little change from earlier in the day, but has weakened since Sunday when it was circulating maximum winds around 100 mph, said aircraft commander Jim Hitterman during a brief period away from the flight deck.
“It seems to be decreasing in size at this time,” he said.
During the overnight mission, the Hurricane Hunters found Guillermo was packing maximum winds around 85 mph at flight level and taking a more northerly track than previously thought, Kyle Larson, the squadron’s aerial weather reconnaissance officer, said shortly before the WC-130J touched down in Honolulu. The five-man crew was slated to take off for another round of data collection Tuesday morning.
With the data added to forecast models, Central Pacific Hurricane Center forecasters were able to adjust the forecast track, putting Guillermo on a path north of the Big Island.
“The track has for the last several cycles shifted farther to the north, or away, from the islands,” said Tom Evans, acting director at the Honolulu-based hurricane center. “The aircraft data is invaluable. The recon they provide gives us a much better idea of where the center is and that data also goes into the forecast models, which allow us to give better forecasts. With that recon data we are more confident than with just the satellite data.”
Guillermo maintained maximum sustained winds of 70 mph at the sea surface and was moving toward the northwest at 9 mph. Increased vertical shear is working to weaken the storm to 60 mph today and 45 mph on Thursday.
The storm was located 350 miles east of the Big Island and boasted tropical storm-force winds extending outward up to 175 miles from its center on Tuesday afternoon. Guillermo was expected to pass 150 miles west-northwest of the island tonight.
The current Central Pacific Hurricane Center forecast calls for up to 3 inches of rain to fall across the island, as Guillermo tracks by today and Thursday. Some isolated high elevation areas could receive up to 7 inches of rain. Swell associated with Tropical Storm Guillermo continues to produce large surf along east-facing shores of all islands, with Big Island faces set to peak around 12 feet Tuesday night before beginning to subside today.
Rainfall amounts will be lower if Guillermo tracks farther away from the islands than currently forecast, however. Should that occur, leeward areas might see more muggy conditions like those that occurred as the remnants of Ela passed north of the state in mid-July.
“Right now, the strong winds are diminishing and the chances of (Guillermo) getting into the Big Island are diminishing, but we will hold on to the watch for a little bit longer — just until we are totally confident that the storm might move away from us,” Evans said.
Little change in strength is forecast for Guillermo today, however, the storm should begin to slowly weaken thereafter as it encounters westerly wind shear. The cyclone should be downgraded to a tropical depression by the end of the week as it moves north of and away from the Hawaiian Islands.
Email Chelsea Jensen at cjensen@westhawaiitoday.com.
