Tropical Storm Haishen (2008) - Meteorological History

Meteorological History

Late on November 14, 2008, The Japan Meteorological Agency (JMA) reported that a minor tropical depression had formed 490 km (300 mi) to the southeast of Iwo To. The JMA then started issuing advisories on the depression early the next day while the Joint Typhoon Warning Center (JTWC) reported that Tropical Cyclone formation was unlikely within the next 24 hours. This was because multispectral satellite imagery had shown that deep convection was developing along the eastern portion of a transitioning Tropical upper tropospheric trough. A QuickScat pass had also shown that a circulation which had previously been confined to the middle of the depression had spawned the development of a low level circulation center. They also reported that the depression currently had a subtropical cold core but was transitioning into a tropical warm core circulation and that a trough of low pressure had introduced increasing vertical wind shear.

Later that day the JMA designated the low as a full tropical depression while later that afternoon, the JTWC reported that deep convection was now persisting along the eastern portion of a low level circulation center, and that the core was now a fully warm tropical core. Despite the low level circulation center progressing rapidly into an area of increasing vertical wind shear, the JTWC issued a Tropical Cyclone Formation Alert on the system. During that evening the JMA upgraded the depression to a tropical storm and named it Haishen whilst, at the same time the JTWC designated Haishen as Tropical Depression 25W while it was located 900 km (560 mi) to the east of Iwo To.

Early on November 16, the JTWC upgraded the Haishen to a Tropical Storm and at the same time Haishen had reached both its 1-minute and 10-minute peak intensity with winds of 75 km/h (45 mph). At this time the JTWC reported that vertical wind shear had increased over the previous 12 hours, which had kept most of the deep convection confined to the eastern portion of the low level circulation center. They also reported that Haishen was traveling along the north portion of a subtropical ridge to the southeast of the system. Microwave imagery had shown that dry air was starting to wrap around the western part of the low level circulation center, they also noted that prefrontal features had appeared on satellite imagery which suggested that extratropical transition had started. The JTWC then issued their final warning later that day as they thought that Haishen was rapidly taking on extratropical characteristics and had lost most of its deep convection, frontal features had also become more pronounced within the last twelve hours. However, the JMA kept issuing advisories on Haishen for another 24 hours before declaring Haishen as extratropical. The extratropical low of Haishen accelerated towards the International Dateline and crossed into the central Pacific later that day. As an extratropical low, the system reintensified to storm intensity but weakened into a 65 km/h (40 mph) gale early on November 21.