Public Information Statement
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
$$
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