Been watching Hermine off the coast and I noticed the term Post-Tropical was being used, I thought when the hell did that start using that?
The answers is 15 May, 2010,
The official NWS notice is here.
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.
Here is what the NWS says it means:
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.
The old terms were extratropical and remnant low, NWS still plans to divvy up post-tropical.
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/.