Invest

Western Pacific Invest · WP912026

21.8°N, 141.9°E

Moving Stationary

Max Winds

35 mph

Pressure

996 mb

Forecast Points

JMA Winds (10-min avg)

35.0 kt

JMA Pressure

994.0 hPa

JMA (10-min average): Typhoon No. 2617 · Nangka

Summary

Invest 91W currently has maximum sustained winds near 35 mph and is moving east at about 12 mph. It is located about 182 nautical miles south of Iwo To, with a broad, still-forming low-level circulation and thunderstorms stretched across the center. Conditions are only marginally favorable right now, but include low wind shear, warm ocean waters, and strong outflow high in the atmosphere. The Joint Typhoon Warning Center says formation of a significant tropical cyclone is possible within the next 12 to 24 hours. Forecast guidance is in good agreement that the system will become more organized and intensify over the next 24 hours while moving briskly to the northeast, generally along a corridor extending from near its current area toward the north-northeast over open waters east of Japan.

Key messages

A significant tropical cyclone could form from Invest 91W within the next 12 to 24 hours.
The system is expected to move briskly northeastward and gradually become more organized over the next 24 hours.
Invest 91W is currently located south of Iwo To, and interests in the area should closely monitor updates.

Satellite Imagery (IR)

CIRA/RAMMB · 12 Aug 03:20 UTC

JTWC Warning 12 Aug 00:00 UTC

WTPN21 PGTW 120000
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 91W)//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
140 NM EITHER SIDE OF A LINE FROM 21.6N 141.7E TO 29.0N 150.0E
WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 27 TO 33 KNOTS. METSAT
IMAGERY AT 120000Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 21.8N 141.9E. THE SYSTEM IS MOVING EASTWARD AT 10 KNOTS.
2. REMARKS:THE AREA OF CONVECTION (INVEST 91W) PREVIOUSLY LOCATED NEAR 
21.9N 141.8E IS NOW LOCATED NEAR 21.8N 141.9E, APPROXIMATELY 182 NM 
SOUTH OF IWO TO. ANIMATED ENHANCED MULTISPECTRAL IMAGERY DEPICTS AN 
ELONGATED, ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) BEGINNING TO 
FORM ALONG THE NORTHERN EDGE OF THE MONSOONAL SOUTHWESTERLY FLOW BELT, 
WITH A LINEAR ARRANGEMENT OF CONVECTION DRAPED ACROSS THE CENTER FROM 
SOUTHWEST TO NORTHEAST. A 112318Z ASCAT-B SCATTEROMETER PASS SHOWS AN 
ILL-DEFINED, NASCENT CIRCULATION WITH A RADIUS OF MAXIMUM WINDS OF ABOUT 
90 NM, WITH MAXIMUM WINDS OF 30-35 KTS WITHIN THE MONSOON BELT ALONG ITS 
SOUTHERN PERIPHERY AND LIGHTER WINDS OF AROUND 20 KTS IN OTHER 
QUADRANTS. ENVIRONMENTAL ANALYSIS FOR THE AREA INDICATES MARGINALLY 
FAVORABLE CONDITIONS FOR DEVELOPMENT WITH LOW VERTICAL WIND SHEAR (5-10 
KTS), WARM SEA SURFACE TEMPERATURES (29-30 C), AND STRONG DUAL-CHANNEL 
OUTFLOW ALOFT. GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 91W WILL BECOME 
MORE SYMMETRIC AND INTENSIFY OVER THE NEXT 24 HOURS WHILE MOVING BRISKLY 
NORTHEASTWARD. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 27 TO 33 
KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 996 MB. THE 
POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN 
THE NEXT 24 HOURS IS UPGRADED TO HIGH.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 
130000Z.
//
NNNN

Products not available for West Pacific storms

NEXRAD radar — no radar coverage over the open West Pacific.
Storm-surge inundation — no public storm-surge model for this basin.
Wind-speed probabilities — JTWC does not publish them.
Watches and warnings — issued by local agencies (PAGASA, JMA, CWA), not JTWC.
Reconnaissance aircraft — no routine aircraft reconnaissance in the West Pacific.
Rapid-intensification and shear diagnostics — SHIPS-based guidance is not published for this basin.

These are data-availability limits for the West Pacific basin, not omissions.

Source: U.S. Navy/Air Force Joint Typhoon Warning Center (JTWC), via the UCAR Tropical Cyclone Guidance Project. JTWC data is in the public domain. · Updated 2026-08-12 02:16 UTC · JMA analysis: Source: Japan Meteorological Agency (10-minute average winds). Satellite imagery: CIRA/RAMMB.