Tropical Storm Faxai (2007) - Meteorological History

Meteorological History

Tropical Storm Faxai began as an area of convection that persisted about 805 kilometers (500 mi) west of Guam on October 24. Satellite imagery indicated broad cyclonic turning in the lower levels of the atmosphere, and a trough was located near the surface. Convection consolidated around the center of the low-level circulation, and the upper-level environment—low wind shear and good divergence—favored development. The following day, the Japan Meteorological Agency (JMA) classified the system as a tropical depression. Shortly after, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert as convection deepened around a partially exposed low. The storm traveled northwest under the influences of a subtropical ridge to the north. At 0000 UTC on October 26, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) designated the system as a tropical depression and gave it the local name Juaning. Around the same time, the JMA upgraded the depression to a tropical storm and gave it the name Faxai.

The JTWC issued advisories on Faxai, designating it as 20W; however, they classified it as a tropical depression. Several hours later, the storm began to undergo an extratropical transition, with convection persisting mainly in the northwestern portion of the storm and cold, dry air entering into the southwestern portion. At 1200 UTC, PAGASA issued their final advisory on Tropical Storm Juaning as it moved out of their area of responsibility. The JTWC reported that Tropical Depression 20W (Faxai) had become extratropical around this time as it merged with a baroclinic zone. A cold front developed along the southern portion of Faxai, a feature of extratropical cyclones. Around that time, the JMA upgraded Faxai to a severe tropical storm with winds of 95 km/h (60 mph ).

The JTWC subsequently upgraded the depression to a tropical storm based on the development of a well-defined central dense overcast. A shortwave trough located over the Korean peninsula provided a favorable upper-level environment for Faxai to intensify. Early the next day, Faxai began accelerating rapidly towards the northeast in the mid-latitude westerlies. An anticyclone located over Japan created a strong pressure gradient between it and the tropical storm, causing the wind field of Faxai to expand significantly to the northeast. As the JTWC issued their final advisory, they assessed the storm to have reached its peak intensity, with winds of 75 km/h (45 mph ). The JMA also assessed Faxai to have reached its peak intensity at that time, with winds of 100 km/h (65 mph ) and a minimum pressure of 975 hPa (mbar); however, the National Oceanic and Atmospheric Administration (NOAA) reported that Faxai had attained hurricane-force winds by this time, peaking at 130 km/h (80 mph). The storm continued towards the northeast at a rapid pace and became extratropical off the eastern coast of Honshu around 1200 UTC on October 27. The extratropical remnants persisted for more than a day before dissipating over open waters late on October 28. NOAA, on the other hand, continued to monitor the remnants of Faxai, with the system reaching the Aleutian Islands on October 29. The following day, the storm rapidly intensified, with the central pressure dropping to 957 hPa (mbar) by 1800 UTC. On October 31, the system tracked into Alaska and weakened.

The Japan Meteorological Agency uses 10-minute sustained winds, while the Joint Typhoon Warning Center uses one-minute sustained winds. The conversion factor between the two is 1.14. JMA's peak intensity for Faxai was 100 km/h (65 mph) 10-minute sustained, or 120 km/h (75 mph) one-minute sustained. The JTWC's peak intensity for Faxai was 75 km/h (45 mph) one-minute sustained, or 65 km/h (40 mph) 10-minute sustained.