NWS Directive (PDF) ...

Effective 15 July 2008, AWC has enhanced its page for International SIGMETs. We changed the name from "International" to "Oceanic" in order to better convey which products can be expected on this page. The Oceanic SIGMET page will show active SIGMETS for the Oceanic FIRs which AWC has SIGMET issuing responsibility. These FIRs are: New York Oceanic, San Juan, Miami Oceanic, Houston Gulf, and a large portion of Oakland Oceanic. These areas are colored a light blue.

On occasion, users may see other SIGMETs displayed in the darker blue areas. These SIGMETs are issued by other offices, but we can not guarantee that all other SIGMETs will be displayed. At the present time, SIGMETs for Mexico, Central and South America, Asia, Alaska, Greenland, are not shown on this web page. We advise users to please contact your flight briefing service to obtain SIGMETs for any oceanic or international flight.

An AWC Oceanic SIGMET (SIGnificant METeorlogical Information) advises of weather potentially hazardous to all aircraft. The purpose of this information is to advise pilots of the occurrence or expected occurrence of en-route weather phenomena which may affect the safety of aircraft operations. Criteria for Domestic and AWC Oceanic SIGMETs are similiar, however the format, contractions, and wording used are different. AWC Oceanic SIGMETs are issued for oceanic areas Pacific and Atlantic adjacent to the United States by a Meteorological Watch Office (MWO). The National Weather Service has MWOs at Anchorage, AK, Honolulu, HI, and the Aviation Weather Center in Kansas City, MO.

AWC Oceanic SIGMET criteria:

  • Thunderstorms
    • Tornadoes
    • Lines of thunderstorms
    • Embedded thunderstorms
    • Large areas of thunderstorms
    • Large hail
  • Tropical cyclone
  • Severe icing
  • Severe or extreme turbulence
  • Duststorms and sandstorms lowering visibilities to less that three (3) miles
  • Volcanic Ash

These SIGMET items are considered to be widespread because they must be affecting or be forecast to affect an area of at least 3000 square miles at any one time.

AWC Oceanic SIGMETs are issued for 6 hour periods for volcanic ash events, 6 hours for hurricanes and tropical storms and 4 hours for all other criteria. If conditions persist beyond the forecast period, the SIGMET is updated and reissued.