Typhoon Roke (2011)

Typhoon Roke (Onyok)

Typhoon (JMA scale)
Category 4 (Saffir–Simpson scale)
Typhoon Roke near peak intensity and approaching Japan on September 20
Formed	September 9, 2011
Dissipated	September 24, 2011
(Extratropical after September 22)
Highest winds	10-minute sustained: 155 km/h (100 mph) 1-minute sustained: 215 km/h (130 mph)
Lowest pressure	940 hPa (mbar); 27.76 inHg
Fatalities	13 total
Damage	$120 million (2011 USD)
Areas affected	Japan, Russia
Part of the 2011 Pacific typhoon season

Typhoon Roke, known in the Philippines as Tropical Storm Onyok, was a powerful and persistent tropical cyclone that affected Japan, including some areas that had been damaged by another typhoon just a few weeks prior. It was the fifteenth named storm, the tenth severe tropical storm, the sixth typhoon of the 2011 Pacific typhoon season and overall, the 27th tropical cyclone to be monitored by the Japan Meteorological Agency during the year.

On September 8, the Joint Typhoon Warning Center started to monitor a tropical disturbance that had developed about 935 km (580 mi) to the northeast of Hagåtña, Guam. Unorganized deep convection was surrounding the disturbances developing low level circulation centre, in an area of low vertical windshear and improving outflow. During that day the disturbance gradually developed further while moving westwards under the influence of a subtropical ridge of high pressure. During September 9, as the system continued to move westwards, the Japan Meteorological Agency reported that the disturbance had developed into a tropical depression. Continuing to move westwards the system gradually developed further with the depressions low level circulation centre consolidating before it was declared Tropical Depression 18W by the Joint Typhoon Warning Center during the next day.

Over the next two days, the system gradually drifted west and intensified slightly, prompting the Joint Typhoon Warning Center (JTWC) to issue a Tropical Cyclone Formation Alert (TCFA) on it. Convection gradually consolidated the LLCC and the JTWC initiated advisories on the system on September 11, designating it with 18W. The next day, the depression drifted into the Philippine Area of Responsibility (PAR) and the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) initiated advisories on the depression, naming it Onyok. However, just as similar to Kulap, Onyok also exited the PAR in 6 hours from entering the region. In an advisory, the JTWC reported that there were at least two more vortices associated with the system, that caused an abrupt, erratic movement. However, being located in an area of warm sea surface temperatures and low vertical wind shear, the depression continued to strengthen and on September 13, the JMA upgraded the depression to a tropical storm and named it Roke.