1989 Pacific Typhoon Season - Season Summary

Season Summary

Throughout 1989, several large-scale factors across the western Pacific Ocean displaced unusual characteristics that presented unique difficulties to forecasters. In their annual tropical cyclone report for 1989, the Joint Typhoon Warning Center regarded the season as one of the most challenging and unique years in their history. During much of the year, a very broad monsoon trough was present and resulted in significant diurnal fluctuations in convective activity that inhibited rapid development of many disturbances. The mid-tropospheric ridge was unusually narrow and led to difficulties in forecasting straight-running storms. Additionally, the Tropical Upper Tropospheric Trough (TUTT) had a major role in the development of many systems, most notably Typhoon Gordon which formed from a single thunderstorm underneath a TUTT cell.

The season began with the unusual development of Tropical Storm Winona east of the International Dateline in early January. Remaining active for two weeks, the system crossed the basin before dissipating over the Philippines. Following a three month lull in activity, a powerful typhoon developed in mid-April and was the second system in nine years to become a super typhoon during that month. By mid-May, an extensive monsoon trough had become established from the Bay of Bengal eastward into the South China Sea. Typhoon Brenda developed from this trough over the South China Sea and moved inland over southern China before dissipating. The typhoon left an area of enhanced low-level southerly flow in its wake that triggered the development of Typhoon Cecil at the end of the month. Two more storms developed during June – Typhoon Dot and Tropical Storm Ellis. The first was a strong typhoon that developed near the Caroline Islands and moved westward, eventually dissipating over Vietnam. The second was a poorly organized system that moved generally northward and struck Japan.

In early July, a surge in the monsoon trough over the basin resulted in the development of Tropical Storm Faye. While this system was over the Philippines, Typhoon Gordon developed underneath a TUTT cell to the east. Following Gordon's rapid intensification phase, a new tropical storm developed within an area of enhanced divergence associated with the same TUTT cell. Several days later, the monsoon trough became exceptionally active and spawned several consecutive cyclones in late-July: Irving over the South China Sea, Judy near the Mariana Islands, 12W near Taiwan, and Ken–Lola around the Ryukyu Islands. The development of seven tropical cyclones in July made it the most active July since 1973. The extreme activity continued into August with the formations of Mac, Nancy, Owen, Peggy, and 19W, all of which formed within the monsoon trough. The rapid succession of Nancy, Owen, and Peggy led to several days of binary interaction between the systems well to the south of Japan. Tropical Storm Roger developed near the Ryukyu Islands a few days after 19W dissipated and rapidly tracked northeastward through Japan. This was the only storm of the month not to develop within the monsoon trough. The final system of August, 21W, developed to the northeast of Guam and dissipated due to strong wind shear.