The eastern Pacific Ocean rages, already surpassing seasonal highs for hurricane activity as powerful storms such as Lowell and Polo have impacted assets from the Mexican mainland to as far away as the Hawaiian Islands.
But in the Atlantic basin, notorious for its heavy parade of storms, it's been strangely quiet with a strong El Niño in play. No hurricanes at all, even as the season has entered its climatological peak.
That lull, however, hasn't brought to a halt the research conducted by tropical cyclone experts at the University of Miami. While the bulk of their investigations typically focus on storm activity in the Atlantic and the Gulf of Mexico, the hyperactive season in the Pacific has provided fertile ground to ensure their work hasn't come to a stop.
One of them is Lynn "Nick" Shay, an oceanographer at the Rosenstiel School of Marine, Atmospheric, and Earth Science.
After a slew of his weather-monitoring devices were deployed into Hurricane Polo this week during Hurricane Hunter reconnaissance flights, Shay has taken another major step forward in learning more about a key parameter used to calculate and convert wind speed into wind stress at the ocean surface in tropical cyclones.
"The surface drag coefficient is a dimensionless number we don't know a lot about. There's so much uncertainty surrounding it," Shay said of that key parameter. "It can either go up or down at high winds, or it can remain the same. So, our ultimate goal is to obtain more data points, particularly under very high wind conditions, about what that drag coefficient might actually look like."
As part of Shay's Office of Naval Research-funded study, some 20 expendable weather measurement sensors—from dropsondes and current profilers to ocean drifters and Airborne eXpendable BathyThermograph, or AXBT, devices—were deployed from two National Oceanic and Atmospheric Administration (NOAA) P-3 Orion aircraft nicknamed Kermit and Miss Piggy.
Benjamin Jaimes de la Cruz, an associate scientist in Shay's Upper Ocean Dynamics Laboratory, deployed the instruments during three flights into Polo when the hurricane, now a post-tropical cyclone, was at its strongest. He manned a data-receiving station aboard the aircraft, analyzing some of the data as it was transmitted via radio signal from the instruments.
The ocean temperature, salinity and current data collected will prove indispensable in Shay's research of the surface drag coefficient's impact on wind stress.
"And learning more about a hurricane's wind stress is crucial for a whole bunch of reasons, not the least of which is projecting storm surge—in other words, how much energy from the atmosphere is being transferred into the current and the wave field," Shay said.
After fieldwork, researchers will conduct testing in the Rosenstiel School's Alfred C. Glassell Jr. SUrge-STructure-Atmosphere INteraction (SUSTAIN) wind-wave tank, simulating conditions they encountered in the field to refine their results, according to Shay.
The study is part of Shay's ongoing research on the surface drag coefficient that has stretched back for decades. "We've been doing this with our expendables for a while, so we have a nice database about where these things fit in," he said.
Also, this is not the first time that storm activity in the eastern Pacific has been one of the centerpieces of Shay's research. Back in 2001, he was part of a joint NOAA and National Science Foundation project called EPIC (the Eastern Pacific Investigation of Climate) in which scientists observed and studied the coupled ocean-atmosphere processes in that area of the Pacific.
And 10 years ago, he and scientists at NOAA's Hurricane Research Division conducted a postanalysis of Hurricane Patricia. That storm, which occurred during an El Niño year and registered maximum sustained winds that topped out at an incredible 215 miles per hour, smashed records for intensity in the Western Hemisphere before smashing into Mexico's southwestern coast on Oct. 23, 2015.
With the El Niño climate pattern suppressing hurricane activity in the Atlantic while driving a surge in the number of storms in the Pacific, this hurricane season has been one of the strangest Shay has ever seen. But El Niño, which is characterized by unusually warm ocean temperatures in the equatorial Pacific, isn't the sole reason for the ramp up in Pacific hurricanes this year.
It is a combination of two factors: warm ocean temperatures and strong salinity in the upper ocean layer that is preventing ocean cooling, according to Shay. "And that means more heat for the atmosphere," he said. "That's something that is often overlooked by forecasters."
Shay maintains scientific websites showing daily ocean heat content and sea surface temperatures for both the Atlantic and Pacific oceans. When Polo was at full strength, his site reported ocean temperatures well above what is needed to maintain a hurricane.
Hurricane extra
Hurricane Hunter pilots and a team of scientists from the Rosenstiel School's Cooperative Institute for Marine and Atmospheric Studies (CIMAS), a NOAA Center of Excellence, flew out of Harlingen, Texas, to collect data on Hurricane Polo that satellites could not measure.
"Not a single hurricane in the Atlantic but gangbusters in the eastern and central Pacific," CIMAS scientist Jason Dunion, who flies on many Hurricane Hunter fights, said in describing this storm season. "We do most of our flying in the Atlantic, but we do occasionally fly out of Hawaii if it's under threat, and it has been a lot this season. Less often, we fly out of Costa Rica or Harlingen to cover storms off of Mexico, either for operations or to do some research."
Polo may have dissipated, but the Hurricane Hunters are still busy in the region, flying out of Texas to capture data on another Pacific hurricane: Rachel.
