Tropical Weather Discussion
Issued by NWS
Issued by NWS
596 AXPQ20 PGUM 220441 AAA TWDPQ Tropical Weather Discussion...UPDATED National Weather Service Tiyan GU 241 PM ChST Tue Sep 22 2026 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... Updated for issuance of TCFA for Invest 91W. TROPICAL AND MONSOON DISTURBANCES... Update: Invest 91W has continued to organize through the day. This morning scatterometry showed a tightening low-level circulation surrounded by convection in all quadrants. Based on these trends, the Joint Typhoon Warning Center upgraded Invest 91W from medium to high, issuing a Tropical Cyclone Formation Alert. A TCFA means that development into a significant tropical cyclone is expected within 24 hours. Previous: The Joint Typhoon Warning Center`s Invest 91W is currently located near 12N143E. The JTWC has upgraded Invest 91W to medium, which means development into a significant tropical cyclone is not expected within 24 hours, but is likely within the next few days. Invest 91W has vastly improved in structure overnight and is beginning to consolidate. Invest 91W is expected to move northwest away from both the Marianas and Yap over the next couple of days. For more information on Invest 91W, see bulletins issued by JTWC under WMO header ABPW10 PGTW. ...OTHER WEATHER SYSTEMS... MONSOON TROUGH... The monsoon trough enters the region at 14N130E and extends east- southeast where it intersects Invest 91W at 12N143E. The trough then extends northeast to 15N148E where it meets a col. Scattered to numerous showers and isolated thunderstorms are seen along the monsoon trough. The monsoon trough will shift northward over the coming days bringing showers and thunderstorms to the Marianas later this week. SURFACE TROUGHS... A surface trough extends from the right side of a col at 14N155E and extends eastward into a broad circulation centered near 13N165E. The trough extends southeastward until it reaches a second col at 10N180. Scattered to numerous showers and isolated thunderstorms are seen where the trough interacts with the broad circulation. Elsewhere, isolated showers are seen across the trough. This trough will remain nearly stationary over the coming days. A second trough extends north of the circulation at 13N165E to 24N170E. Scattered to widespread showers and isolated thunderstorms are seen along the trough axis. This trough will move west over the next few days. TUTT... A TUTT enters the region at 25N170E and extends west-southwest into a TUTT cell near 20N143E. Little to no shower activity is seen along the TUTT. However, the TUTT appears to be helping ventilate Invest 91W and the weak circulation at 13N165E. The TUTT will continue to move westward and intensify over the next day or two. $$ Williams