Amid favorable conditions, Noru rapidly intensified into the season's first super typhoon, and reached peak intensity with annular characteristics on July 31.

[6] Although outflow was weak for the partially organized system at that time, low vertical wind shear and sea surface temperature (SST) at 29 °C were conducive to development.

[8] At 12:00 UTC, the system intensified into the fifth Northwest Pacific tropical storm of 2017,[5] which was assigned the international name Noru half a day later by the JMA operationally.

[10] 12 hours later, the JTWC upgraded Noru to a tropical storm, despite its partially exposed LLCC; at the same time, it started tracking westward along the southwest periphery of the subtropical ridge (STR) positioned to the northeast.

[11] Noru struggled to intensify significantly for two days owing to relatively low ocean heat content values and its asymmetric structure,[12] until it developed into a severe tropical storm at around 18:00 UTC on July 22.

[15] After that, the eye repeatedly reappeared and filled due to increasing vertical wind shear offset by improving poleward outflow into the upper-low associated with Tropical Storm Kulap.

[19] Although vertical wind shear relaxed somewhat with the robust eastward outflow channel on July 26, the reduction of mid-level relative humidity and slightly depressed SSTs at 26 °C to 27 °C tempered intensification and even eroded the convective structure.

[20] Having finished a cyclonic loop and tracking west-northwestward along the southern periphery of a deep-layered ridge to the northeast, Noru showed some signs of transitioning to a hybrid system, with an upper-level low nearby and a thermal structure more indicative of a subtropical storm.

[23] At the same time, the steering flow transitioned to the subtropical ridge centered over the East China Sea, causing Noru to track southwestward along the eastern boundary of this STR.

Despite warmer SSTs at 28 °C to 29 °C which supported intensification for Noru in the area, the complex upper-level environment with a TUTT cell to the southeast and a ridge far to the north combining limit outflow, while dry air continued enveloping the typhoon and isolating it from any significant moisture.

[25] 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.

The typhoon took on annular characteristics, with a symmetric ring of deep convection surrounding a 30 km (19 mi) well-defined eye and fairly uniform cloud top temperatures.

[28] On July 31, Noru reached its peak intensity at around 00:00 UTC with ten-minute sustained winds at 175 km/h (109 mph) and the central pressure at 935 hPa (27.61 inHg).

[5] 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.

[29] 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.

[33] Having tracked westward relatively faster for one day, Noru slowed down again and turned northwestward on August 4, along the southern periphery of a deep-layered subtropical ridge over the Korean Peninsula and western Japan.

[35] On August 5, deep convective banding presented predominantly in the southern semi-circle of Typhoon Noru, owing to strong equatorward outflow and the terrain of Kyushu as well as the Ōsumi Islands.

[37] Noru remained almost stationary and looping around Yakushima until it accelerated northeastward off the southeastern coast of Kyushu on August 6, along the western boundary of a deep-layered ridge extension located to the southeast.

[40] Thus, the JTWC downgraded Noru to a tropical depression about five hours later and issued their final warning owing to the poorly-defined and disorganized LLCC in the afternoon.