Joint Typhoon Warning Center Marks 50 Years of Service
By Bob Freeman
Special to American Forces Press Service
WASHINGTON, Nov. 13, 2009 This year marks the 50th anniversary of the Joint Typhoon Warning Center, a joint Navy and Air Force office that provides tropical cyclone reconnaissance and forecasting to support the safety of military and other government assets in the U.S. Pacific Command and U.S. Central Command areas of responsibility.
“The Joint Typhoon Warning Center was established by the United States Pacific Command in 1959. It actually formed out of the consolidation of several smaller tropical forecast centers that were scattered throughout the Pacific region, and those were actually created in the wake of what's known as Typhoon Cobra,” said Navy Lt. Cmdr. Jeremy Callahan, operations officer at JTWC, in a Nov. 10 interview on Pentagon Web Radio’s audio webcast “Armed with Science: Research and Applications for the Modern Military.”
Callahan described Typhoon Cobra, which hit vessels of the Pacific Fleet in 1944, as one of the worst naval disasters in U.S. history. According to a fleet letter from Navy Adm. Chester Nimitz, the Pacific Fleet’s commander in chief at the time, 790 sailors were lost and 80 were injured, three ships sank and nine suffered serious damage, and 146 aircraft on various ships were lost or damaged beyond repair.
Callahan explained that a typhoon is a western Pacific version of a hurricane. Both constitute the most developed and severe form of tropical cyclones, which are large storms that form over warm tropical waters.
The Joint Typhoon Warning Center ensures that today’s military forces in the Pacific will never again experience a disaster like Typhoon Cobra. Callahan said the center, which is composed of a mix of Navy, Air Force and civilian meteorologists and analysts, provides tropical cyclone guidance, advisories and warnings to U.S. military and government assets throughout the Pacific region.
The center’s actual forecasting responsibilities are in the western Pacific and Indian oceans. Callahan explained that the civilian National Hurricane Center and Central Pacific Hurricane Center share tropical cyclone forecasting responsibilities for the Atlantic and the Pacific region east of the International Dateline.
“We actually only do the forecasting west of the dateline,” Callahan noted, “but our area includes both the northern and southern hemispheres.” Since the seasons are reversed in the southern hemisphere, that means the center is kept busy throughout the year.
“So it's a year-round job here, and with both hemispheres in the Pacific and Indian Ocean, we actually cover about 89 percent of the world's tropical cyclones,” Callahan said. He explained that JTWC provides forecasts to military bases and ships, U.S. embassies, and U.S. territories such as Guam that fall under their area of responsibility.
“Our main products are the storm track, the horizontal extent of the winds and the intensity of the systems,” Callahan said. “These forecasts are very complex, so we use very large numerical models that are run on super computers. We actually have a large suite of these computer models. Some are run here at Joint Typhoon Warning Center, but most are run elsewhere.
“For instance,” he continued, “the Navy has some models that are being run at the Fleet Numerical Meteorology and Oceanography Center. The National Center for Environmental Prediction, which is [the National Oceanic and Atmospheric Administration’s] computing center, runs some of these models. The Air Force Weather Agency runs a model for us.”
He added that the center also uses computer models operated by Japan, Australia, the United Kingdom, and the European Center for Medium Range Weather Forecasts.
Callahan noted that the models all have their strengths and weaknesses. Some are global in scope, depicting the atmosphere over the entire Earth, and some are regional, providing a higher-resolution look. He explained that the larger models are useful for overall atmospheric flow and forecasting a storm’s track.
“But we need the smaller regional models to be able to determine the structure of the cyclone, what the winds are, and how the system is actually behaving within the local environment,” he added.
“We are getting excited about the Navy's global model called NOGAPS, which is starting to do a new four-dimensional data assimilation,” Callahan said. “Instead of just getting a static picture, it's able to identify trends in the data and, hopefully, get a better initialization before the model starts to run.
“We have also just implemented the Navy's regional model, COAMPS,” he continued. “It has a specialized tropical cyclone tracker that we're currently evaluating, and the Air Force Weather Agency is running a regional model called WRF that also is starting to implement a tropical cyclone tracker. So there's a lot of good model development right now, and some other research that we're starting to get excited about.”
As for tropical cyclone reconnaissance, Callahan said JTWC monitors storms through a suite of remote sensing technologies set on geostationary and polar-orbiting satellites, along with shore and ship observations and surface radar imagery.
“The No. 1 tool we use is called the scatterometer, and that's able to give us a direction and wind speed of winds at the surface over the ocean,” Callahan explained. “It does this through the polarization of microwave energy reflected off the little capillary waves, the tiny one- and two-millimeter waves that are being caused by the wind as it goes over the surface of the ocean.”
In addition to traditional weather satellites normally used to track storm movement, Callahan described the use of such space-based sensing devices as microwave imagers and sounders, infrared and water vapor imagers, and radar altimeters. All combine to provide an understanding of the shape, structure, size, intensity and movement of the storm.
Callahan noted that the center has a public-facing Web site that offers regular tropical cyclone warnings, text and graphical products, satellite imagery, and significant weather bulletins. He cautioned, however, that JTWC services are primarily for the Defense Department, and while it may be useful to review the products, viewers should consult their local national meteorological agency for products pertinent to their locality.
(Bob Freeman works in the Office of the Oceanographer of the Navy.)