Throughout January 17 the tropical storm would again oscillate in strength , resulting in a brief downgrade by the JTWC to tropical depression intensity . However , an increase in deep convection resulted in its reclassification as a tropical storm at 1800 UTC that day , followed by the JMA upgrading the system to tropical storm intensity at 1200 UTC on January 18 . As such , the storm received the name Yanyan . At roughly the same time , the tropical cyclone began to stall east of the Mariana Islands and curve sharply northeastward . Whilst the JTWC indicated that Yanyan peaked in strength late on January 18 with 1 @-@ minute sustained winds of 60 km / h ( 37 mph ) , the JMA considered the system to have maintained the same intensity throughout its stint as a tropical storm . Steered by the same nearby subtropical ridge , Yanyan would continue to track towards the northeast into a less favorable tropical cyclone environment . The JMA downgraded Yanyan to tropical depression at 1200 UTC on January 20 before the storm transitioned into an extratropical cyclone as its low @-@ level circulation center decoupled from the primary mass of convection due to strong wind shear . At 0000 UTC , both the JTWC and JMA discontinued the monitoring of Yanyan .