# Tropical Storm Yagi (2018)

Tropical Storm Yagi, known in the Philippines as Tropical Storm Karding, was a moderate but damaging tropical cyclone that was part of the 2018 Pacific typhoon season. Yagi started its lifetime as an area of low-pressure, located southwest of Iwo To on August 1. The system struggled to intensify for five days until it was recognized as a depression by the JMA on August 7. JTWC later followed suit and went ahead to designate it as Tropical Depression 18W. It maintained its intensity due to easterly wind shear, despite the system being well organized. Both agencies upgraded into a tropical storm on the next day after showing winds of 35 knots.
Yagi later curved towards the northwest, battering with moderate wind shear. JTWC later reached its 1-minute peak intensity of 50 mph on August 12. Shortly after this, Yagi made landfall in Wenling in Zhenjiang, China. As it moved inland, JTWC continued tracking as an extratropical cyclone before issuing a final warning on August 16.

## Meteorological history

Yagi's origins are traced back to July 31, when it formed as a tropical disturbance near 18°00′N 136°00′E﻿ / ﻿18.0°N 136.0°E﻿ / 18.0; 136.0. On August 1, the Joint Typhoon Warning Center (JTWC) began monitoring the disturbance that persisted 806 km (501 mi) southwest of Iwo To. The system had a broad area of low level clouds circulating below flaring thunderstorms—or atmospheric convection—possessing adequate divergence aloft and situating over warm sea surface temperatures of 28–29 °C (82–84 °F) and low vertical wind shear—conditions which are favorable for tropical cyclogenesis. At 06:00 UTC, the Japan Meteorological Agency (JMA) recognized it as a low-pressure area, before deeming it too weak early the next day. The JMA then categorized it again on August 4, before last noting it for the second time until August 5 as it was nearly stationary. By August 6, the JMA reported that the system had intensified into a tropical depression east of the Philippines and had began moving westward. PAGASA had also began tracking the system as it was within its responsibility area, giving it the local name Karding. At 18:00 UTC of that day, the JTWC designated the system Tropical Depression 18W, though it was characterized as having a poorly-defined center and being unorganized.
During August 7, the system began forming rainbands into its fully-exposed center, though its convection was displaced to the west by an increase of wind shear. Its motion was influenced by a weak near-equatorial ridge it binded with to the southeast. However, the wind shear was somewhat offset by diffluence in the upper troposphere, allowing deep convection to intensify, as multiple mesovortices in the center were apparent on satellite imagery. As it continued to battle vertical wind shear with equatorward outflow, the system moved erratically in a north-northwestward direction while 948 km (589 mi) south-southeast of Kadena Air Base, Japan. By 00:00 UTC of August 8, the JMA reported that the tropical depression had intensified into a tropical storm, assigning it the name Yagi. The JTWC followed suit in upgrading the system six hours later due to a scatterometer pass, as Yagi turned east-northeast due to being in between the near-equatorial ridge and a subtropical ridge. On August 9, Yagi again turned north-northwestward along the southwestern edge of the subtropical ridge, with thunderstorms beginning to bloom very close to the center. Later on, a dense overcast partially obscures the center over marginal environmental conditions, as outflow continued to improve. Despite sea surface temperatures remaining high, Yagi was over a region of low ocean heat.
On August 10, Yagi briefly became nearly stationary while slowly moving west-southwestward, with convection concentrated over the southwest quadrant, though it resumed its original northwestward track. Nascent thunderstorms then began broadening over the western flank of the storm, despite persistent high wind shear. Moreover, radar imagery revealed fragmented deep banding wrapping into the storm's center as it shifted westward. Around 01:00 UTC on August 11, PAGASA reported that Yagi had exited the Philippine Area of Responsibility. At 12:00 UTC, the JMA reported that Yagi had attained its peak intensity, estimating maximum sustained winds of 75 km/h (45 mph) and the lowest atmospheric pressure of 990 hPa (29.23 inHg). A tropical upper tropospheric trough cell to the north-northwest enhanced poleward outflow, allowing for additional intensification in conjunction with warm waters. At 12:00 UTC in August 12, the JTWC reported that Yagi had attained 1-minute maximum sustained winds of 85 km/h (50 mph) while 285 km (177 mi) north-northeast of Taipei, Taiwan. At 15:35 UTC, Yagi made landfall over the coast of Wenling, Zhejiang, China, prompting the JTWC to issue its final warning at 18:00 UTC. Yagi then began to weaken during August 13 due to land interaction. At 00:00 UTC, Yagi had weaken into a tropical depression, according to the JMA and JTWC. The system then recurved eastward on August 14 and entered the Bohai Sea—where it transitioned into an extratropical cyclone at 06:00 UTC of August 15—turning southward and then southwestward before fully dissipating 24 hours later on August 16.

## Impact

Although Yagi (Karding) didn't make landfall in the Philippines, the storm enhanced the southwest monsoon which brought extreme flooding towards many regions within the country. According to the NDRRMC, 5 people died along with ₱996 million (US$19 million) worth of damages. In East China, Yagi killed a total of 3 people and total damages were counted to be CN¥2.51 billion (US$367 million).