Tropical Storm Vongfong (2008) - Meteorological History

Meteorological History

Early on August 13, the Joint Typhoon Warning Center, noted that an area of convection had persisted approximately 370 nautical miles (690 km) to the southeast of Okinawa, Japan and designated it as a Tropical Disturbance. The JTWC at this time also assessed the disturbances chances of forming into a significant tropical cyclone within 24 hours as fair. This was due to the tropical disturbance having a broad Low Level Circulation Center however the strongest winds were displaced on the eastern side of the disturbance. Early the next morning the JTWC reassessed the disturbances chances of forming into a significant tropical cyclone within 24 hours as good and issued a Tropical Cyclone Formation Alert on the developing disturbance. This was because the Low Level Circulation Center had become well defined.

Later on August 14, the Japan Meteorological Agency designated the tropical disturbance as a minor tropical depression whilst the JTWC also upgraded the disturbance and designated it as Tropical Depression 12W. Early the next day the JMA designated the depression as a full tropical depression, whilst the JTWC upgraded the depression to a tropical storm. Later that day the JMA upgraded the depression to a tropical storm, and assigned the name Vongfong to the storm. The Joint Typhoon Warning Center then reported that Vongfong had reached its peak winds of 50 knots (60 mph, 95 km/h) whilst it was located approximately 390 nautical miles (720 km) to the southwest of Tokyo, Japan. The JMA also then reported that it Vongfong had reached its operational peak winds of 40 knots (45 mph 75 km/h ) however this was later revised in its best track when the JMA upgraded Vongfong peak winds to 50 knots (60 mph 110 km/h ). Later on August 15, the JTWC reported that Vongfong had started to weaken from its peak. During the next day Vongfong carried on weakening. The JTWC then issued its final warning on Vongfong later that day as it had begun its extratropical transition. whilst the JMA kept issuing warnings on Vongfong until early on August 17 when they downgraded it to an extratropical low. The extratropical low of Vongfong then crossed the International Dateline and moved out of the JMA’s area of responsibility and moved into the Central Pacific Hurricane Center's area of responsibility but they did not issue any warnings on Vongfong as it was extratropical.