The Joint Typhoon Warning Center (JTWC) updated its tropical cyclone warning products Nov. 1 to reflect marked improvements to wind distribution predictions due to a tropical cyclone.

The changes, driven by priorities set by U.S. Pacific Command for tropical cyclone forecasting, provide a more accurate depiction of wind uncertainty for U.S. and coalition forces operating near a tropical cyclone. Wind structure forecasts are critical for mission planners preparing for an approaching storm. The degree to which gale and destructive force winds extend from a tropical cyclone heavily influences decisions regarding installation preparations, aircraft evacuations, and ship sortie and routing options.

"New techniques enable us to analyze, forecast, and verify tropical cyclone surface wind distribution with much more accuracy," said Cmdr. Jillene Bushnell, JTWC commanding officer. "The improvements allow for planning and preparation well in advance of an impending tropical cyclone, and were only possible through a collaborative research effort led by Charles "Buck" Sampson and the rest of his team at the Naval Research laboratory (NRL) Monterey, California, as well as contributors from the Cooperative Institute for Research in the Atmosphere (CIRA), the National Oceanographic and Atmospheric Administration (NOAA), and JTWC."

On JTWC's warning graphic, wind distributions are displayed as lines encircling the system separated into four quadrants. Three separate radii circles represent the extent of gale strength winds (34 knots), destructive strength winds (50 knots), and typhoon strength winds (64 knots).

Previously, wind distributions were only forecast out to three days and were not included for positions over land, on subtropical systems, or when the system became extratropical due to the complex wind patterns and notable inaccuracies.

Using a more accurate forecasting approach, now users can see wind distribution on all forecast positions as long as the wind radii remains at or above gale strength; however, wind distribution remains valid only over areas of open water.

"Extending wind distribution forecasts out to five days will also show improvement to the 34-knot danger swath, the shaded area surrounding a tropical cyclone's track on our graphic," said Brian Strahl, JTWC senior scientist. "The danger swath is a representation of the area where gales could potentially be found based on the size of the tropical cyclone and past JTWC forecast track errors. Previously, the swath size or shape could become unrealistic without wind radii on days four and five of the forecast because JTWC had to extrapolate the swath for the extended forecast based on the 72-hour wind radii forecast. By extending wind distributions to all JTWC forecast positions, the swath is computed at all lead times, providing a more consistent and accurate product."

In addition to the warning graphic, details for the wind distribution forecasts are also found on JTWC's warning text products and Google Earth kmz files available at https://metoc.ndbc.noaa.gov/JTWC/.

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 Group 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.

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