|
Tropical Depression 18W was a weak, short-lived tropical cyclone that brought heavy rains to parts of the Mariana Islands ahead of the more intense Typhoon Melor. Forming from an area of low pressure on September 26, 18W was first monitored by the Japan Meteorological Agency (JMA) as a tropical depression. Tracking generally towards the west, deep convection gradually developed around the system and the Joint Typhoon Warning Center (JTWC) issued their first advisory on the depression early on September 28. Although the depression initially struggled to maintain deep convection, it eventually became better organized and was upgraded to a tropical storm on September 29 by the JTWC. Several hours after reaching this intensity, the system began to rapidly dissipate as its inflow and outflow were severely disrupted by two nearby storms, Parma to the west and Melor to the east. The cyclone fully dissipated near Guam early on September 30 before being absorbed by Typhoon Parma. Ahead of the system's arrival in Guam, tropical storm watches and warnings were issued by the National Weather Service. On September 29, a state of emergency was declared by Governor Felix P. Camacho and relief funds were allocated in case of damage after the storm. Due to the low-intensity of the storm, it had little impact on Guam. Only increased winds and moderate rainfall were reported. ==Meteorological history== The storm originated from an area of low pressure on September 24 that formed roughly 725 km (450 mi) east-northeast of Pohnpei. Deep convection had developed in association with the low and was beginning to wrap around the center of circulation.〔〔 By September 26, the system had developed strong outflow and was intensifying. Later that day, the Japan Meteorological Agency (JMA) began monitoring the low as a tropical depression. The following day, the Joint Typhoon Warning Center (JTWC) issued their first advisory on the depression. At this time, it was being steered towards the west in response to a mid-level ridge to the north. Little intensification took place as convection barely deepened around the low-level circulation; however, the JTWC anticipated the system to intensify into a tropical storm within 24 hours. Although conditions for intensification were present, convection associated with the depression weakened significantly by September 28. Forecasts for the system became increasingly complicated due to the formation of Tropical Depression Nineteen-W to the east-south-east. Later that day, the motion of the storm shifted to the west-northwest in response to a subtropical ridge north of the depression. The center of circulation had become nearly devoid of convection late on September 28, with only the western portion of the system featuring shower and thunderstorm activity. By the morning of September 29, convection redeveloped around the center of 18W and the JTWC determined that the system had intensified into a tropical storm, with winds peaking at 65 km/h (40 mph 1-minute sustained). However, in post storm analysis, the JTWC determined that the depression had not intensified into a tropical storm and lowered the peak wind-speeds to 55 km/h (35 mph).〔 Around the time the system was upgraded to a tropical storm by the JTWC, the JMA assessed it to have reached its peak intensity as a strong tropical depression with winds of 55 km/h (35 mph 10-minute sustained) and a barometric pressure of 999 mbar (hPa).〔〔 Struggling to maintain deep convection, the system's inflow and outflow patterns became severely disrupted by two intensifying cyclones, Parma to the west and Melor to the west. The combined effects of the two other storms eventually left the center of 18W devoid of convection as it approached Guam. As it passed near the island, the storm rapidly dissipated, first weakening to a depression and then losing its low-level circulation. It was no longer considered a tropical cyclone a few hours after brushing Guam. This coincided with the issuance of the final warnings from the JTWC and the JMA.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tropical Depression 18W (2009)」の詳細全文を読む スポンサード リンク
|