Late on September 4, an area of low pressure developed to the southeast of Okinawa, Japan. Over the next two days, the system drifted north and developed a well defined LLCC with organized convective banding, prompting the JMA to upgrade the low pressure area to a tropical depression. On September 7, convection consolidated the low-level circulation center very well with tightly curved banding wrapped into it. Also, high sea-surface temperatures and very low wind shear caused the system to undergo rapid deepening, prior to which, the JMA upgraded the system to a tropical storm and named it "Kulap". However, the system stopped strengthening soon after as the LLCC became partially exposed and the convection was displaced to the south. Kulap remained small in size and dry air entering from the western periphery kept it from strengthening further. Wind shear increased, pushing convection about south of the LLCC. Also, Kulap was beneath a tropical upper tropospheric trough (TUTT cell) that caused subsidence. A mid-level subtropical steering ridge cuased Kulap to track in a northwestward direction. On September 8, Kulap moved into the east-northeast periphery of the Philippine Area of Responsibility (PAR) prompting the PAGASA to start issuing advisories on the system, naming it "Nonoy". However, Kulap quickly accelerated north and exited the PAR on the same evening, prompting the PAGASA to issued their final advisory on the system. After increasing wind shear caused further weakening, the JTWC downgraded Kulap to a tropical depression late on September 8. Early on September 10, the JMA too downgraded Kulap to a tropical depression, and continued to track Kulap's remnants as a tropical depression until it finally dissipated early on September 11.
Early on September 8, a cluster of thunderstorms came together as a low pressure area with imporoving outflow and a developing low-level circulation center (LLCC). Later that day, the JMA upgraded the low pressure area to a tropical depression north-northeast of the Northern Mariana Islands. Over the next two days, the system gradually drifted west and intensified slightly, prompting the 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 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 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". On September 17, Roke developed a small, deep convective eye promoting the JMA to upgrade Roke to a severe tropical storm with winds of over . Between September 19 and 20, Roke underwent "Explosive intensification", a more extreme case of rapid deepening that involves a tropical cyclone deepening at a rate of at least 2.5 mbar per hour for a minimum of 12 hours. Also, they added that Roke developed a eye and a good poleward outflow channel. On September 21, Typhoon Roke made landfall over Hamamatsu, Japan at about 5:00 UTC (14:00 JST). Soon Roke started weakening as cloud tops started getting warmed up and eye diameter started to decrease. However, the system still maintained a near radial outflow and the convective structure continued to remain organized that kept Roke from dissipating rapidly. Although Roke entered a de-intensification phase, it still had plenty of strength that posed a great threat to regions of Japan. Being about southwest of Yokosuka, Kanagawa, the typhoon accelerated north-northwestward at about with winds of over (1-min sustained) being a Category 3 typhoon on the SSHS. Being embedded in the baroclinic zone, Roke started its extratropical transition. Also, land interaction severely weakened the storm to a minimal Category 1 typhoon with winds of under (1-min sustained). Only six hours later, the storm further weakened and accelerated northeastward at about with rapidly dissipating deep convection completely sheared to the northeast of the LLCC. As a result, the JTWC ceased advisories on the storm, as it became fully extratropical.
Early on September 13, a low pressure area formed northeast of the Northern Mariana Islands. The system gradually drifted north and steadily intensified until the next day when the JMA upgraded the system to a tropical depression. Later on September 14, the JTWC issued a Tropical Cyclone Formation Alert (TCFA) on the system reporting that the system could intensify into a tropical storm within 24 hours from then. Convection rapidly consolidated the center with persistent, deep convection around the northeastern periphery, prompting the JTWC to initiate advisories on the system, designating it with "19W". Soon, the JMA also initiated advisories on the system, upgrading it to Tropical Storm "Sonca". In the begging, Sonca seemed to have intensified rapidly since formation, however, soon the storm weakened back to a minimal tropical storm because of dry air entering the LLCC that caused it to elongate and weaken. However, that was not for too long as vigorous convection persisted over the well defined LLCC with tightly curved banding wrapped in, Sonca continued to strengthen gradually and the JTWC reported winds of at-least near the center. As Sonca continued to strengthen, and the JMA upgraded it to a severe tropical storm on September 17. Later that day, Sonca developed a large ragged eye with deep convective banding tightly wrapped into it. As a result, Sonca strengthened more rapidly and by early the next day, it became a typhoon. On September 18, Sonca reached a peak intensity of (1-min mean) and (10-min mean) and soon the convection around the northern periphery started weakening. Being embedded in a baroclinic zone with low sea surface temperatures, Sonca started its extratropical transition late on September 19. The transition took place relatively fast because of a frontal boundary and the JTWC reported that Sonca became extratropical early on September 20, while the JMA did the same later in the evening.
Early on September 14, the JMA started monitoring a cluster of thunderstorms to the southeast of Taiwan as a tropical depression. But because of the land interaction, the system could not be empowered and the JMA stopped tracking the depression late on September 15, as the system dissipated.
In the evening of September 21, a low pressure area developed to the east-southeast of Palau. The low gradually drifted west and became more well organized prompting the JTWC to issue a Tropical Cyclone Formation Alert (TCFA) on it. Later, the LLCC became well organized with flaring deep convection developing around it, so the JMA started monitoring the low as a tropical depression. Later on September 23, the JTWC also initiated advisories on the system designating it with "20W". Early on September 24, the JMA further upgraded 20W to a tropical storm and named it "Nesat". Nesat continued to drift west with expanding deep convection around the entire system and consolidating convection around the LLCC. The mid-level warm anomaly near the system continued to intensify and convective banding near the LLCC became more and more tighter. As a result, the JMA upgraded Nesat to a severe tropical storm on September 25. Late on the same day, the JMA further upgraded Nesat to a typhoon.