Tropical Storm 60W

60W was an unusual low-pressure system persisting west of the International Date Line in 2006. Originally forming as an extratropical cyclone on November 2, the system tracked generally southeastwards, and it received the designation 60W when becoming subtropical late on November 6. On the next day, 60W acquired more tropical characteristics, although it was not recognised as a tropical cyclone by the Japan Meteorological Agency and Joint Typhoon Warning Center. 60W began to weaken and turned southwestwards on November 8, and it dissipated south of Wake Island three days later.
Meteorological history
Early on November 2, an extratropical cyclone formed about east of Tokyo, Japan. The system moved very slowly and gained gale strength on November 3. After becoming a developed low and finishing an anticlockwise loop on November 4, the system started to move southeastwards and weaken slightly on the next day. However, late on November 6, the Japan Meteorological Agency (JMA) reported that the low began to intensify again, as well as the QuikSCAT data shows winds of 45 to 50 knots on the west side of the system. The Satellite Services Division (SSD) of the National Oceanic and Atmospheric Administration started to use the Dvorak technique to analyse the system and initially estimated it ST3.0 later, indicating a subtropical storm with increased convection near the centre.
Consequently, the U.S. Naval Research Laboratory designated the system as 60W, but contents were soon hidden and not accessible via the tropical cyclone page. JMA reported that 60W started to develop again early on November 7, when convection had begun wrapping around the west side of the centre. Several hours later, SSD analysed that the system weakened slightly, but deeper convection began to develop closer to the centre, mainly in the northwest and southeast corners. Late on the same day, deep convection continued banding around the centre, and 60W has become a shallow symmetric warm-core system. Thus, SSD indicated that 60W had transitioned to a tropical storm.
Early on November 8, plenty of dry air started to wrap around 60W. Subsequently, JMA declared that 60W had become developed, when the system began to drift southwestwards. Deep convection faded away more and more, resulting the system to weaken. Late on the same day, 60W was largely devoid of convection; therefore, JMA reported that 60W was below gale intensity, as well as SSD issued the final bulletin on the unclassifiable system. Since that, although JMA still considered 60W as an extratropical cyclone, it only maintained a low-level circulation centre without deep convection. On November 9, 60W passed through the Tropic of Cancer and arrived at the tropics, yet the system eventually dissipated early on November 11, about south of Wake Island.
Nature of the system
60W has been considered as an extratropical, subtropical, or tropical cyclone by different agencies and experts. The Japan Meteorological Agency, which also operates the RSMC Tokyo, recognised the system as an extratropical low. Karl Hoarau, a geographer teaching in the Cergy-Pontoise University, regarded 60W as a typical subtropical cyclone, which formed from an occluded cyclone. David Roth of the Weather Prediction Center noted that when 60W was located over 23 to 24ºC sea surface temperature on November 7, thunderstorms had broken out on the north side of the centre, as well as the depth of convection was greater than an occluded cyclone.
The Satellite Services Division (SSD) of the National Oceanic and Atmospheric Administration, however, regarded 60W as a subtropical cyclone initially, later a tropical cyclone. The bulletin issued on November 7 reported that:
Convection has begun to band around the center. Florida State and Penn State University analyzed cyclone phase diagrams based on the 12Z 07 November GFS run indicates this is a shallow symmetric warm core system. The system has transitioned to tropical. 4.5 tenths banding results in a DT of 2.5. PT2.0. FT of 2.5 is based on DT.<ref namenov7 />

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