User:Meow/Subtropical Storm 60W

Subtropical Storm “60W” was a low-pressure system persisting west of the International Date Line in 2006, showing possibly extratropical, subtropical, or tropical characteristics. Forming as an extratropical cyclone on November 2, the system tracked generally southeastwards, and it acquired subtropical features late on November 6. On the next day, the cyclone acquired more tropical characteristics, although it was not recognised as a tropical cyclone by the Japan Meteorological Agency and Joint Typhoon Warning Center. The cyclone 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 2350 km 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 the cyclone 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 the cyclone about 650 km west of Midway Atoll has become a shallow symmetric warm-core system. Thus, SSD indicated that the cyclone had transitioned to a tropical storm.

Early on November 8, plenty of dry air started to wrap around the cyclone. Subsequently, JMA declared that the cyclone 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, the cyclone was largely devoid of convection; therefore, JMA reported that the cyclone was below gale intensity, as well as SSD issued the final bulletin on the unclassifiable system. Since that, although JMA still considered the system as an extratropical cyclone, it only maintained a low-level circulation centre without deep convection. On November 9, the cyclone passed through the Tropic of Cancer and arrived at the tropics, yet the system eventually dissipated early on November 11, about 370 km south of Wake Island.

Nature of the system
The cyclone 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 the cyclone as a typical subtropical cyclone, which formed from an occluded cyclone. David Roth of the Weather Prediction Center noted that when the cyclone was located over 23 to 24 °C 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 the cyclone 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. PT=2.0. FT of 2.5 is based on DT."