NOUS41 KWBC 151954 PNSWSH SERVICE CHANGE NOTICE 10-06 NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC 255 PM EST FRI JAN 15 2010 TO: SUBSCRIBERS: -FAMILY OF SERVICES -NOAA WEATHER WIRE SERVICE -EMERGENCY MANAGERS WEATHER INFORMATION NETWORK -NOAAPORT OTHER NWS PARTNERS...AND NWS EMPLOYEES FROM: THERESE Z. PIERCE CHIEF...MARINE AND COASTAL SERVICES BRANCH SUBJECT: ADOPTION AND USE OF /POST-TROPICAL CYCLONE/ TERMINOLOGY BY NWS NATIONAL CENTERS AND FORECAST OFFICES: EFFECTIVE MAY 15 2010 ON MAY 15 2010...THE NWS WILL BEGIN USING THE TERM /POST- TROPICAL/ TO DESCRIBE WEATHER SYSTEMS THAT ARE NO LONGER TROPICAL CYCLONES. THIS CHANGE WILL MAKE NWS TERMINOLOGY CONSISTENT WITH THE TERMINOLOGY USED BY OTHER WORLD METEOROLOGICAL ORGANIZATION MEMBER STATES. IT WILL ALSO ALLOW THE NWS TO MORE ACCURATELY DESCRIBE THE METEOROLOGICAL STRUCTURE OF FORMER TROPICAL CYCLONES. THE FOLLOWING DEFINITION FOR POST-TROPICAL CYCLONE WILL BE INCLUDED IN THIS SEASON/S UPDATE OF NWS INSTRUCTION 10-604: TROPICAL CYCLONE DEFINITIONS. POST-TROPICAL CYCLONE...A FORMER TROPICAL CYCLONE. THIS GENERIC TERM DESCRIBES A CYCLONE THAT NO LONGER POSSESSES SUFFICIENT TROPICAL CHARACTERISTICS TO BE CONSIDERED A TROPICAL CYCLONE. POST-TROPICAL CYCLONES CAN CONTINUE CARRYING HEAVY RAINS AND HIGH WINDS. FORMER TROPICAL CYCLONES THAT HAVE BECOME FULLY EXTRATROPICAL...AS WELL AS REMNANT LOWS...ARE TWO SPECIFIC CLASSES OF POST-TROPICAL CYCLONES. AS SUGGESTED BY THE ABOVE DEFINITION...THE NWS WILL CONTINUE TO USE THE MORE SPECIFIC TERMS OF /REMNANT LOW/ AND /EXTRATROPICAL/ ... WHEN APPLICABLE... TO PROVIDE ADDITIONAL INFORMATION ON THE TYPE OF SYSTEM THE TROPICAL CYCLONE HAS OR IS EXPECTED TO BECOME. UPDATED DEFINITIONS OF REMNANT LOW AND EXTRATROPICAL CYCLONE FOLLOW. REMNANT LOW...A POST-TROPICAL CYCLONE THAT NO LONGER POSSESSES THE CONVECTIVE ORGANIZATION REQUIRED OF A TROPICAL CYCLONE...AND HAS MAXIMUM SUSTAINED WINDS OF LESS THAN 34 KNOTS. THE TERM IS MOST COMMONLY APPLIED TO THE NEARLY DEEP-CONVECTION-FREE SWIRLS OF STRATOCUMULUS IN THE EASTERN NORTH PACIFIC. EXTRATROPICAL CYCLONE...A CYCLONE OF ANY INTENSITY FOR WHICH THE PRIMARY ENERGY SOURCE IS BAROCLINIC /THAT IS...RESULTS FROM THE TEMPERATURE CONTRAST BETWEEN WARM AND COLD AIR MASSES/. THE FOLLOWING EXAMPLE SHOWS HOW THE NEW TERMINOLOGY WOULD BE USED IN THE TABLE SECTION OF A TROPICAL CYCLONE DISCUSSION PRODUCT FOR THE LAST ADVISORY ON A DECAYING TROPICAL STORM. IN THIS EXAMPLE...THE SYSTEM HAS LOST THE DEEP CONVECTION REQUIRED OF A TROPICAL CYCLONE BUT IT DOES NOT YET HAVE ANY FRONTAL CHARACTERISTICS. IN ADDITION THE SYSTEM CANNOT BE DESIGNATED A REMNANT LOW BECAUSE ITS MAXIMUM WINDS EXCEED 34 KNOTS. THEREFORE THE SYSTEM IS MERELY DESCRIBED AS POST-TROPICAL AT THE INITIAL TIME. IN 24 HOURS...HOWEVER...THE SYSTEM IS FORECAST TO CHANGE STRUCTURE AND BECOME A FRONTAL LOW. THE /EXTRATROPICAL/ DESIGNATION IS THEREFORE APPENDED IN THE TABLE TO INDICATE THIS FORECAST CHANGE IN STRUCTURE. FORECAST POSITIONS AND MAX WINDS INITIAL 01/1500Z 46.5N 46.5W 40 KT...POST-TROPICAL 12HR VT 02/0000Z 48.9N 45.6W 40 KT...POST-TROPICAL 24HR VT 02/1200Z 52.2N 43.5W 40 KT...POST-TROP/EXTRATROP 36HR VT 03/0000Z 55.0N 39.8W 40 KT...POST-TROP/EXTRATROP 48HR VT 03/1200Z 56.0N 33.0W 40 KT...POST-TROP/EXTRATROP 72HR VT 04/1200Z 56.5N 20.0W 40 KT...POST-TROP/EXTRATROP 96HR VT 05/1200Z...ABSORBED THE NHC IS RESPONSIBLE FOR ALL METEOROLOGICAL DECISIONS CONCERNING FORECASTING OF TROPICAL AND SUBTROPICAL SYSTEMS FOR THE ATLANTIC OCEAN AND THE EASTERN PACIFIC OCEAN...NORTH OF THE EQUATOR AND EAST OF 140 DEGREES WEST LONGITUDE. THE CPHC IS RESPONSIBLE FOR ALL METEOROLOGICAL DECISIONS CONCERNING FORECASTING OF TROPICAL AND SUBTROPICAL SYSTEMS FOR THE PACIFIC OCEAN NORTH OF THE EQUATOR FROM 140 DEGREES WEST TO 180 DEGREES WEST LONGITUDE. IF YOU HAVE QUESTIONS...PLEASE CONTACT: TIMOTHY SCHOTT NATIONAL WEATHER SERVICE MARINE AND COASTAL SERVICES BRANCH 1325 EAST WEST HWY ROOM 13126 SILVER SPRING MARYLAND 20910 301-713-1677 EXT 122 NATIONAL SERVICE CHANGE NOTICES ARE ONLINE AT /USE LOWERCASE/: HTTP://WWW.WEATHER.GOV/OS/NOTIF/HTM $$ NNNN
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