Tropical Storm Lan developed northwest of Palau on Monday. At 5:00 p.m. EDT on Monday the center of Tropical Storm Lan was located at latitude 10.7°N and longitude 132.1°E which put it about 275 miles (445 km) north-northwest of Koror, Palau. Lan was moving toward the west at 12 m.p.h. (19 km/h). The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h). The minimum surface pressure was 993 mb.
A more distinct center of circulation developed within Tropical Storm Lan, but the low pressure system was still in the process of organizing. The low level center of circulation of Lan was at the end of a long rainband that extends from the western periphery around the southern and eastern parts of the tropical storm. That low level center appeared to be on the northern side of a much larger counterclockwise rotation. Most of the stronger showers and thunderstorms were occurring in the long rainband. A few new, thinner bands of showers and thunderstorms seemed to be forming inside the long rainband to west of the center of circulation.
Tropical Storm Lan will be moving through an environment that will be favorable for intensification. Lan will move over water where the Sea Surface Temperature is near 30°C. An upper level ridge north of Lan is producing easterly winds which were blowing toward the top of the circulation. There was some vertical wind shear, but it was not strong enough to prevent the intensification of Tropical Storm Lan. Tropical Storm Lan is likely to intensify more slowly while the circulation organizes. Once the center of circulation become tighter, then Lan could intensify more quickly. A period of rapid intensification could occur, if Lan becomes a typhoon and an eye develops.
The ridge north of Lan and the counterclockwise flow to its south are combining to steer the tropical storm toward the west. Numerical models are indicating that a weakness will develop in the ridge north of Tropical Storm Lan. If that happens, then the steering current could weaken for 12 to 24 hours and Tropical Storm Lan might not move much. If the break in the ridge becomes more pronounced, then Tropical Storm Lan could start to move more toward the north. On its anticipated track Tropical Storm Lan is expected to remain east of the Philippines, but the tropical storm could move closer to the northern Philippines if the forecast weakness in the ridge does not occur.