2009-Typhoon Lupit (22w) #2 (Long Report)

Updated at 2009-10-24 14:30 HKT

Short Description

The severe tropical storm Lupit, located about 520 kilometers south-southwest of Okinawa, is expected to move away from the northern Philippines with low speed. The scenario has changed a little bit. As Lupit started tracking northeast, it is no longer to move further close to the extreme northern Luzon and make landfall on Taiwan. It is now forecasted to be persistently steered by the weak extend of high pressure ridge located to the east of it. And in the long-range forecast, it will enter the mid-level westerly wind flow and start accelerating to the east.

Synoptic Circulation Analysis

From the latest Korea Meteorological Administration’s 500hPa analysis chart(shown in figure 1), delivered at 2009-10-24 12:00 HKT, there is a large-scale polar vortex over Siberia(西伯利亞極地渦旋), causing the cold and dry air mass in the vicinity of it to flow further south. Therefore, there is significant temperature gradient over the northern China(shown in figure2).

Figure 1 –Korea Meteorological Administration’s 500hPa analysis chart

Figure 2 –Temperature gradient chart from ECMWF

There was a nearly-omega blocking system (阻塞形勢) in the mid-latitudes(shown in figure 3). The blocking high (阻塞高壓) was built near Kamchatka Peninsula (勘察加半島) due to the strong warm advection (暖平流). The westerly jet flow bypass the stable blocking high and divided into northern as well as southern air flows. It contributes to the vorticity advection (渦度平流) to the northern blocking high and helps the building and maintaining of long-wave low pressure trough (長波槽). As the blocking high was stably located near Kamchatka Peninsula, the trough kept stationary with the base of it reached over Taiwan. The building of this blocking high is the explanation to the northeastern track of Lupit.

Figure 3 –Korea Meteorological Administration’s 500hPa analysis chart at

2009-10-23 00:00 HKT

However, from the latest Korea Meteorological Administration’s 500hPa analysis chart(shown in figure 1), the blocking high seems “breaking down”, causing the next long-wave trough adjustment in the mid-latitudes (長波調整).

Strength Analysis

Based on the synoptic circulation analysis above, the dry and cold air will feed into the weakening circulation system until the next long-wave trough adjustment. The animated infrared imagery shows continued weakening of deep convection. Although the mid-level trough helped to strengthen the system’s poleward outflow, the core of Lupit will still be deteriorating under these unfavorable conditions with the maximum wind speed not exceeding 100km/h in 10-min average.

It is forecasted that Lupit will failed to regain much strength after the next long-wave trough adjustment as it will enter an area of increasing wind shear due to the strong upper-level winds.

It is expected that Lupit will bring minimal damage to the coastal areas of extreme northern Luzon and Taiwan. It is visible in the ensemble tropical rainfall potential chart (shown in figure 4 and 5), the outer rainbands will not spreading across the Philippines and Taiwan and the coverage of the rainbands keep decreasing.

Figure 4 –ensemble tropical rainfall potential chart for rainfall >25mm with 0-6hr forecast period

Figure 5 –ensemble tropical rainfall potential chart for rainfall >25mm with 12-18hr forecast period

Track Analysis

Lupit is expected to be steered northeast by the influence of the weak extend of high pressure ridge and embedded in the westerly mid-level trough which will cause it to move northeast to east with acceleration. For this movement, the core shall pass within 400km to the south of Okinawa. However, it is expected that Lupit will bring only light rainfall with strong or gale wind to the region.

There is another scenario for the track of Lupit. It has the potential to move equaterward after the next long-wave trough adjustment with the base of trough move across Lupit. However, it leads to the blocking of divergence channel and there will be again the intrusion of dry air in the mid and upper levels. For this scenario, it has low probability to happen.

Organization Cyclone Information:

+ HKO(10-min avg): STS90 km/h
+ JMA(10-min avg): STS90 km/h
+ CWB(10-min avg): STS90 km/h
+ JTWC#41(1-min avg): STS95 km/h