Typhoon Doksuri formed over the Philippine Sea last week and quickly reached super typhoon status. Now it has made landfall in the Philippines while weakening. In the coming days, Taiwan will also be marginally affected before the storm finally dissipates over mainland China.
Pacific Typhoon Season
Tropical storms can form in the western Pacific at any time of the year, but the main season is limited to the period between May and October. We are in the middle of the season, so to speak. Since April, several tropical storms have formed, most notably Typhoon Mawar, which caused great destruction on Guam, among other places.
Fig. 1: Typhoon Mawar over the Philippine Sea on May 26, 2023 ; Source: Wikipedia
Doksuri so far
About a week ago, a tropical depression formed over the Philippine Sea. On July 21, it reached tropical storm status and was named Doksuri; in the Philippine region, the storm is also known as Egay. By July 23, the system had strengthened to the point where it exceeded winds of 118 km/h, by definition becoming a typhoon. Doksuri deepened rapidly in the following days, peaking on July 25 with a core pressure of 925 hPa and 10-minute average winds of nearly 240 km/h (gusts of nearly 300 km/h). Early Wednesday morning (local time, Tuesday evening CEST), it made landfall on Fuga Island in Aparri (Cagayan province). Earlier, it weakened somewhat due to land interactions. A few hours later, the tropical storm made landfall a second time in Dalupiri.
Fig. 2: Infrared image of Doksuri just before it hit land; Source: Tropical Tidbits
In addition to destructive winds, a lot of rain fell in a short period of time. In Baguio, for example, official measurements showed 396 mm within 24 hours. Other stations along the Philippine north coast also recorded 250 to 300 mm. Such extreme precipitation totals occur on the one hand due to the very humid air masses of the tropical storm, but also the topography plays a major role. The Cordillera Central is an extensive mountain range on the island of Luzon and extends over a length of 320 kilometers from north to south, the highest mountain (Mount Pulag) is almost 3000 meters high. Like all tropical storms in the northern hemisphere, Doksuri rotates counterclockwise, leading to increased upslope precipitation on the windward side (the side facing the current) of a mountain range. On the leeward side, on the other hand, little rain falls. This becomes visible in the following illustration with the opposite precipitation values on the two mountain sides of the island.
Fig. 3: Rainfall totals fallen in the past 24 hours in the northern part of Luzon; Source: Ogimet
Further draught
The typhoon will continue its northwesterly track under further weakening in the coming days. Even though it will not directly hit Taiwan, the distinct cloud bands will provide a lot of moisture input, leading to large amounts of rain. According to current models, Doksuri will reach mainland China between Xiamen and Shantou on Friday and eventually dissipate quickly.
Fig. 4: Further track of Typhoon Doksuri; Source: JTWC
Similar to current conditions on Luzon, rainfall on Taiwan will be very unevenly distributed. The Taiwanese central mountains (Chungyang Range) will protect the northwestern half from the excessive rainfall, but the situation will be different between Hengchun and Hualien. Here, 400 mm are expected until Saturday.
Fig. 5: Forecasted precipitation total on Taiwan until Saturday noon; Source: Weathermodels
