page_title: Typhoon Noru (2017)
section_title: Re-intensification and peak intensity
hierarchical_section_title: Typhoon Noru (2017) / Re-intensification and peak intensity
caption_attribution_description: English: Typhoon Noru south of Japan on August 3, 2017, with an enormous eye surrounded by the donut-like ring.
context_page_description: Typhoon Noru was the second-longest-lasting tropical cyclone of the Northwest Pacific Ocean on record—behind only 1986's Wayne and tied with 1972's Rita—and the second-most-intense tropical cyclone of the basin in 2017, tied with Talim. Forming as the fifth named storm of the annual typhoon season on July 20, Noru further intensified into the first typhoon of the year on July 23. However, Noru began to interact with nearby Tropical Storm Kulap on July 24, executing a counterclockwise loop southeast of Japan. Weakening to a severe tropical storm on July 28, Noru began to restrengthen as it turned sharply to the west on July 30. Amid favorable conditions, Noru rapidly intensified into the season's first super typhoon, and reached peak intensity with annular characteristics on July 31. In early August, Noru underwent a gradual weakening trend while curving northwestwards and then northwards. After stalling off the Satsunan Islands weakening to a severe tropical storm again on August 5, the system began to accelerate northeastwards towards the Kansai region of Japan, making landfall in Wakayama Prefecture on August 7.
context_section_description: Noru reformed an eye at around 09:00 JST (00:00 UTC) on July 29 while situated 70 km (45 mi) to the east of Chichijima, the largest Ogasawara island. Based on the observations from Iwo To, the JTWC downgraded Noru to a tropical storm at around 18:00 UTC, at which time the system was tracking directly southward along the eastern periphery of an extension of the STR positioned to the west. Early on July 30, Noru began to improve its convective structure, making both of the JMA and the JTWC upgrade Noru to a typhoon again. Over the following 24 hours, Noru rapidly intensified, and the JTWC reported that it had become a Category 4 super typhoon about 225 km (140 mi) south of Iwo To at around 18:00 UTC, with one-minute sustained winds at 250 km/h (155 mph), though operationally it was put at Category 5 strength with winds at 260 km/h (160 mph). The typhoon took on annular characteristics, with a symmetric ring of deep convection surrounding a 30 km (15 mi) well-defined eye and fairly uniform cloud top temperatures. Environmental conditions were favorable with radial outflow, enhanced by a poleward outflow channel into the TUTT and a subtropical jet to the east-northeast. Noru's previous southward motion also led itself to the warmer area with SSTs at 29 °C to 30 °C, favoring intensification. At this time, Noru began to drift westward within a competing steering environment.
   
  On July 31, Noru reached its peak intensity at around 00:00 UTC with ten-minute sustained winds at 175 km/h (110 mph) and the central pressure at 935 hPa (27.61 inHg). It remained an impressively annular system with a clear eye but lacking banding features, yet the JTWC downgraded it to a typhoon in the afternoon because of recently warming cloud tops. Traveling northwestward over an area of low ocean heat content and isolated from well-defined outflow, Noru's gradual weakening trend became more evident early on the next day, which is also indicated by the JMA. A microwave imagery depicted a weakened eyewall, while the eye was temporarily not as clear as before. Since late August 1, Noru presented a 95 km (60 mi) diameter large but ragged eye, yet the convective ring surrounding the eye gradually elongated, especially on the northwestern quadrant; meanwhile, microwave imageries even depicted a break from the northwestern portion of the eyewall. Noru was establishing a poleward outflow channel that tapped into a passing mid-latitude trough located to the north on August 2, and a strong near-equatorial ridge was steering the typhoon towards a weak area in the subtropical ridge to the northwest, being the result of that passing mid-latitude trough.
caption: Typhoon Noru slowly weakening with annular features south of Japan on August 3
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