Southern Hemisphere tropical cyclone season from fall 2015 to spring 2016. JTWC tracked nine tropical cyclones in the southern Indian Ocean. (Photo by Joint Typhoon Warning Center)
Southern Hemisphere tropical cyclone season from fall 2015 to spring 2016. JTWC tracked 11 tropical cyclones in the southern Pacific Ocean. (Photo by Lieutenant Caitlin Fine)
Sample modernized warning graphic used by JTWC. (Photo by Lieutenant Caitlin Fine)
PEARL HARBOR —
The first warning on a Southern Hemisphere tropical cyclone was issued Nov. 29, 2017 by the Joint Typhoon Warning Center (JTWC) in Pearl Harbor, Hawaii. Dahlia (Tropical Storm 01S) was the first Southern Hemisphere system where warnings were issued every six hours without higher authority request.
Previously, manpower constraints limited updating warnings to every 12 hours but with the training of two more typhoon duty forecasters and innovative internal business practices, JTWC is now capable of six-hourly warnings regardless of their location in the ocean.
"This periodicity change of warnings specifically enables the U.S. Pacific Command and its components greater fidelity of information on systems threatening their assets, enabling better informed decisions," said Cmdr. Jillene Bushnell, the commanding officer of JTWC. "The previous gap between warnings would regularly result in larger changes in tropical cyclone fix, intensity and forecast track based on a longer interval between forecasts in a chaotic environment. Matching our forecast accuracy and periodicity throughout our assigned Pacific and Indian Ocean regions is extremely important to me."
JTWC releases warnings on tropical cyclones above 35 knot (40 mph) wind speeds in the Pacific and Indian Oceans. Products include a graphic of the tropical cyclone depicting the historical and predicted track, wind speed, and the radius of gale (34 knot), destructive (50 knot), and typhoon (64 knot) strength winds. In addition to the graphic, the products include an explanation of the current environmental situation and forecast philosophy; a text product listing the track, wind speed, and wind radii information in six hour intervals; a satellite image showing the tropical cyclone's center position at the time of the warning; and a Google Earth overlay.
During the 2016 season, JTWC warned on 20 tropical cyclones in the Southern Hemisphere. During February 2016, the strongest Southern Hemisphere tropical cyclone on record, Severe Tropical Cyclone Winston, made landfall on the islands of Fiji with winds estimated up to 185 mph by JTWC. Winston caused almost $500 million in damage and 44 deaths in Fiji, and launched a multinational relief response to help 350,000 affected residents. Upon request, JTWC issued six-hourly warnings for Tropical Cyclone Winston as it approached the islands of Fiji, providing more detailed information that improved preparation, emergency management and follow-on humanitarian assistance and disaster relief operations.
Additionally, starting in 2018 JTWC will update its wind radii colors and graphic color scheme, change the historical track character to dashed and add clarifying information in the legend. The intent is to improve the user experience and first-use understanding. The modernized warning will be issued for tropical cyclones above 25 knots in the western North Pacific Ocean and above 34 knots in the Indian and southern Pacific Oceans.
JTWC provides tropical cyclone reconnaissance, forecast, safety warning and decision support services for operational advantage to U.S. government agencies operating in the Pacific and Indian Oceans.
JTWC also provides tsunami advisory information and recommendations to shore installations and afloat units, as well as maritime impact forecast and decision support services to U.S. Pacific Command subordinate commands, as directed.
JTWC is jointly staffed by U.S. Navy and Air Force personnel and falls under the operational control of Commander, Task Force 80.7-Commander, Naval Meteorology and Oceanography Command. U.S. Air Force personnel are sourced to JTWC by the 17th Operational Weather Squadron, a subordinate squadron of the 557th Weather Wing.