 On January 11 , the JTWC began monitoring the disturbance that would eventually develop into Yanyan near the International Date Line . As the system tracked westward , it gradually moved into a more favorable environment for tropical cyclogenesis . On January 14 , surface observations indicated that the low @-@ pressure area had developed a closed , low @-@ level circulation center indicative of a tropical cyclone , satellite imagery remained inconclusive . Nonetheless , the JMA classified the pressure area as a tropical depression west of the Marshall Islands at 0600 UTC on January 15 . The JTWC would follow suit by classifying the storm as such at 1800 UTC later that day . At the time , the depression was tracking west @-@ northwest under the influence of a subtropical ridge to the north . Over the next day the system waned in convective activity before resuming its previous track and accelerating . At 0000 UTC on January 17 , the JTWC upgraded the system to tropical storm intensity , though the storm remained nameless as the JMA continued to classify it as a tropical depression . 
 On January 11 , the JTWC began monitoring the disturbance <a href='null_relcl' title='1'><mark>that</mark></a>would eventually develop into Yanyan near the International Date Line . As the system tracked westward , it gradually moved into a more favorable environment for tropical cyclogenesis . On January 14 , surface observations indicated that the low @-@ pressure area <a href='been_done' title='2'><mark>had</mark></a> developed a closed , low @-@ level circulation center indicative of a tropical cyclone , satellite imagery remained inconclusive . Nonetheless , the JMA classified the pressure area as a tropical depression west of the Marshall Islands at 0600 UTC on January 15 . The JTWC would follow suit by classifying the storm as such at 1800 UTC later that day . At the time , the depression was tracking west @-@ northwest under the influence of a subtropical ridge to the north . Over the next day the system waned in convective activity before resuming its previous track and accelerating . At 0000 UTC on January 17 , the JTWC upgraded the system to tropical storm intensity , though the storm remained nameless as the JMA continued to classify it as a tropical depression . 
On January 11 , da JTWC began monitoring the disturbance would eventually develop into Yanyan near the International Date Line . As tdasystem tracked westward , it gradually moved into a more favorable environment for tropical cyclogenesis . On January 14 , surface observations indicated that the low @-@ pressure area done developed a closed , low @-@ level circulation center indicative of a tropical cyclone , satellite imagery remained inconclusive . Nonetheless , the JMA classified thdaressure area as a tropical depression west of the Marshall Islands at 0600 UTC on January 15 . ThedaWC would follow suit by classifying the storm as such at 1800 UTC later that day . At the time , the depression was tracking west @-@ northwest under the influence of a subtropical ridge to the dath . ova the ndaday the system waned in convective activity b4 resuming its previous track and accelerating . At 0000 UTC on January 17 , the JTWC upgraded the system to tropical storm intensity , though the storm remained nameless as the JMA continued to classify it as a tropical depression .