Air Force hurricane hunters have been flying WC-130J aircraft through Tropcal Storm Iselle every six hours since Tuesday providing location, wind conditions and other meteorological information to the Central Pacific Hurricane Center.
The aircraft fly through the eye wall of the hurricane, into the eye itself and through the eye wall on the other side at 10,000 feet, increasing the accuracy of forecasts up to 25 percent, the Air Force said.
On a nearly 10-hour mission that returned to Joint Base Pearl Harbor-Hickam at about 3:30 p.m. Thursday, Air Force Reserve crews with the 53rd Weather Reconnaissance Squadron out of Mississippi noted a "disorganized" hurricane that was starting to become ragged but was still packing a lot of punch.
"At 150 miles out we were still getting tropical-storm-force winds above 30 to 35 knots," said meteorologist Maj. Kevin Fryar after touching back down. "So that means basically it’s got a very broad wind field of at least 150 nautical miles."
Four of the aircraft and about 40 to 50 crew members are in Hawaii to track both Iselle and Hurricane Julio following it.
Colder waters around Hawaii, dryer air and upper-elevation wind shear that knock the tops off many hurricanes work in Hawaii’s favor, but Iselle was the exception, said Maj. Jon Brady, an aerial reconnaissance meteorologist with the 53rd squadron.
"There’s a reason why Iselle made it this far, and it appears that through its lifetime in getting here, it developed into what we call an annular hurricane — and they are very rare," Brady said at the unit’s temporary offices at Hickam.
Annular, or "truck tire," hurricanes have an extra-thick eye wall and are resistant to all three factors that usually benefit Hawaii.
"This Iselle has amazingly made it through incredibly harsh conditions. It had three things working against it, and it’s still knocking on our door," Brady said.
Only 3 percent of Pacific hurricanes become annular, he said.
The other rarity with Iselle is that the storm was expected to "crash head-on into" Mauna Loa and Mauna Kea on Hawaii island.
"When a system like this crashes into something that big, it’s going to cause a lot of problems as far as turbulence is concerned," Brady said. "All that fairly steady wind-flow is going to hit (the peaks) and come crashing down, and that’s going to make things very, very turbulent on the ground and aloft."
Brady said he was on one of the unit’s aircraft in 2012 flying into Hurricane Carlotta heading for the west coast of Mexico when the storm hit 10,000-foot mountains "and we got caught up in very wicked turbulence."
"We dropped about a thousand feet in I don’t know how many seconds," Brady said. "I lifted out of my chair, pen went to the ceiling, my papers flew all over. It was scary."
The Air Force hurricane hunters, along with a National Oceanic and Atmospheric Administration P-3 propeller aircraft and Gulfstream G-IV jet that flies at a much higher altitude, have been monitoring Hurricane Iselle, officials said.
The Air Force reservists with the 53rd typically fly through hurricanes at 10,000 feet and tropical storms at 5,000 feet, Brady said.
The aircraft have radar to determine precipitation ahead and wind sensors. In the eye wall, "dropsondes" with parachutes are released to determine the maximum winds at flying altitude and surface level.
"The general public a lot of times assumes that maybe we fly over the hurricanes and look down into them and maybe release instruments into them," Brady said. "We don’t. We fly as low as possible with safety in mind to measure the worst of it."
Hurricane thunderstorm eye walls can reach as high as 50,000 to 60,000 feet, he said.
In the eye of the storm, it can be "completely clear, calm and mild, and winds are near zero," he said. One 53rd member described seeing what looks like a "stadium of cotton balls."
The aircraft often have to "crab" when they fly through the eye wall, meaning they fly sideways to a degree as the circulating winds push the side of the aircraft.
The hurricane hunters were evaluating whether they will be able to continue the weather missions as the hurricane passes over Hawaii island because of the turbulence expected, and are also planning for an alternate landing site in Lihue when the storm reaches Oahu around noon Friday, Brady said.
Air crews will be flying into Julio next, which is expected to reach Hawaii island late Sunday morning, he said.
Fryar, a National Weather Service forecaster in Chicago, said "it feels good" to be able to provide the hurricane-tracking information.
"That’s one of the things we feel like we’re able to serve people by being able to provide this kind of information," he said.