


Tropical Weather Discussion
Issued by NWS
Issued by NWS
027 AXPQ20 PGUM 090121 TWDPQ Tropical Weather Discussion National Weather Service Tiyan GU 1121 AM ChST Wed Jul 9 2025 Tropical Weather Discussion for the Western North Pacific between the Equator and 25N from 130E to 180. The following information is based on recent satellite imagery/data, weather observations, radar, and meteorological analysis. ...SPECIAL FEATURES... None. ...OTHER WEATHER SYSTEMS... MONSOON TROUGH... The monsoon trough extends east of Tropical Storm Danas north of Taiwan, entering the Area of Responsibility (AOR) near 22N130E, continuing towards JTWC`s Invest 91W located near 23N138E and then extending eastward to about 21N145E. Modest west to southwest monsoon flow is occurring generally west and southwest of the Marianas extending across and well south of Palau and Yap State. The active monsoonal pattern looks to continue through tomorrow before a brief breakdown in monsoonal flow occurs as Invest 91W moves generally northwestward. The monsoonal flow is expected to return this weekend with a potential surge near Palau. SURFACE TROUGHS... There are a couple surface troughs across the region. The first is a sharp trough between Pohnpei and Kosrae extending from 5N159E to 13N160E. This trough is producing numerous showers just east of Kosrae where surface convergence and 20 to 25 kt winds are noted on last night`s ASCAT analysis. This feature will move westward bringing active weather for Pohnpei and Chuuk over the next couple of days as the trough amplifies. A sharp trough is seen just west and southwest of the Marianas extending from 12N140E to 16N142E. A weak circulation appears to be embedded within this trough where the monsoon flow and southeasterly flow converge. Scattered to numerous showers and isolated thunderstorms have been developing along this trough this morning. This feature will move northward over the coming days and will potentially merge with Invest 91W as the pattern shifts to the northwest. TUTT... The TUTT extends west across the Date Line at around 25N to an upper- level low centered northwest of Wake Island near 23N164E, then continues west-northwest through 25N154E. Another upper-level low exists to the west of Weno, Chuuk at around 7N147E with a trough extending to the north-northeast to around 16N151E, and another trough stretching southeast to around 5N150E. The two upper lows are somewhat disconnected from one other, separated by an upper-level ridge extending southward over Chuuk Lagoon. The TUTT northwest of Wake Island is interacting with a series of surface troughs to produce scattered showers and isolated thunderstorms across the region, focused to the north and southwest of Wake. This upper-level low looks to shift northwest over the next few days before dissipating this weekend, as the TUTT itself looks to rebuild westward over Wake from across the Date Line. The upper-level low west of Chuuk Lagoon will diminish over the next few days as it meanders westward into Yap State. ITCZ... A disorganized band of convection associated with a weakly-defined ITCZ is seen across eastern Micronesia, extending westward from across the Date Line roughly along 5N. Scattered showers and isolated thunderstorms are seen over the southern RMI to the south of Majuro extending to just east of Kosrae. The ITCZ looks to remain weak and indistinct through the remainder of the week. $$ Williams/DeCou