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AXPQ20 PGUM 121140 AAA
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TROPICAL WEATHER DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TIYAN GU
940 PM CHST WED AUG 12 2026
UPDATED SECTION REGARDING INVEST 91W (TCFA).
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
TROPICAL AND MONSOON DISTURBANCES...
A WEAK DISTURBANCE, INVEST 90W, IS CENTERED NW OF KWAJALEIN NEAR
12.1N 164.8E, MOVING SLOWLY WNW. THE LOW-LEVEL CIRCULATION CENTER
(LLCC) REMAINS RELATIVELY CLOUD FREE, WITH THE ASSOCIATED CONVECTION
SEEN TO THE W OF THE CENTER, ALONG A BAND OF CONVERGENCE S OF A COL
REGION. SCATTERED SHOWERS ARE FOUND IN THIS REGION. INVEST 90W IS
EXPECTED TO CONTINUE TO MOVE SLOWLY WNW OVER THE COMING DAYS WITH
LITTLE CHANGE IN INTENSITY. CONVECTION, HOWEVER, MAY INCREASE CLOSER
TO THE CENTER OF 90W.
A MORE ORGANIZED DISTURBANCE, INVEST 91W, IS CENTERED NEAR 21.9N
143.3E, ABOUT 235 MILES SSE OF IWO TO AND WELL NW OF AGRIHAN IN
THE NORTHERN MARIANAS. INVEST 91W WAS UPGRADED TO HIGH FOR
DEVELOPMENT EARLIER TODAY, NOW THE SUBJECT OF A TROPICAL CYCLONE
FORMATION ALERT BY THE JOINT TYPHOON WARNING CENTER (JTWC), WHICH
MEANS THAT TROPICAL CYCLONE DEVELOPMENT IS EXPECTED WITHIN THE
NEXT 24 HOURS. LATEST SATELLITE DATA AND SURFACE ANALYSIS
CONTINUES TO SHOW A CLOUD COVERED LLCC, WITH LEADING EDGE OF THE
MONSOONAL BELT CURVING ALONG ITS NORTHEASTERN PERIPHERY. OTHER
FACTORS REMAIN FAVORABLE FOR TC DEVELOPMENT AS WELL, WITH LOW
VERTICAL WIND SHEAR, GOOD UPPER-LEVEL OUTFLOW AND WARM SEA
SURFACE TEMPERATURES. MAXIMUM SUSTAINED WINDS ARE ESTIMATED AT 27
TO 33 KNOT WINDS, VERY NEAR TO TROPICAL STORM STRENGTH. TO THE
SOUTH OF 91W, DAYTIME ASCAT DATA SHOWS POCKETS OF GALE-FORCE WINDS
WITHIN THE TRAILING MONSOON SURGE. 91W IS FORECAST TO MOVE
NORTHEASTWARD, CONTINUING TO MOVE AWAY FROM THE MARIANAS AND
EXITING OUR AREA OF RESPONSIBILITY (AOR) THURSDAY AFTERNOON.
ALTHOUGH INVEST 91W IS NOT EXPECTED TO HAVE A DIRECT IMPACT ON THE
MARIANAS, CONVECTION ALONG THE SOUTHERN EDGE OF THE TRAILING
MONSOON SURGE COULD MOVE INTO THE MARIANAS, ESPECIALLY TINIAN AND
SAIPAN NORTHWARD, OVER THE WEEKEND. INVEST 91W WILL CONTINUE TO BE
MONITORED CLOSELY, AND ADVISORIES WILL BE ISSUED AS NEEDED.
FOR MORE INFORMATION ON INVEST 91W, PLEASE SEE BULLETINS ISSUED BY
THE JOINT TYPHOON WARNING CENTER (JTWC) UNDER WMO HEADER ABPW10
PGTW AND WTPN21 PGTW.
..OTHER WEATHER SYSTEMS
MONSOON TROUGH...
THE MONSOON TROUGH ENTERS THE REGION NEAR 25N130E, EXTENDING ESE
INTO INVEST 91W. IT THEN TURNS NE TO BEYOND 25N NEAR 145E, EXTENDING
INTO TD PEILOU. AS PEILOU CONTINUES TO WEAKEN AND MOVE NE, THE
MONSOON TROUGH IS SHOWING SIGNS OF REDEVELOPING FARTHER S, POSSIBLY
INTERACTING WITH INVEST 90W. THIS WILL BE MONITORED OVER THE COMING
DAYS. NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS ARE SEEN ALONG AND
UP TO 300 MILES S OF THE MONSOON TROUGH. AS INVEST 91W CONTINUES
MOVING ENE TO NE, THE MONSOON TROUGH WILL MOVE WITH IT, WEAKENING AS
91W ADVANCES.
SURFACE TROUGHS...
A SURFACE TROUGH EXTENDS SE FROM INVEST 91W INTO INVEST 90W. THIS
TROUGH MAY BE THE ATTEMPT FOR THE MONSOON TROUGH TO RE-ESTABLISH
FARTHER S. A SMALL BAND OF SCATTERED SHOWERS AND A FEW THUNDERSTORMS
IS SEEN TO THE E OF THE FAR NORTHERN CNMI. FARTHER S, SCATTERED TO
NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS ARE FOUND W OF THE
TROUGH, N OF POHNPEI AND KOSRAE. AS INVEST 90W DRIFTS W, THE TROUGH
AND ASSOCIATED CONVECTION ARE EXPECTED TO STRENGTHEN, WITH INCREASING
CONVECTION ALONG THE TROUGH. THIS DOES NOT LOOK SUFFICIENT TO
DEVELOP INVEST 90W, JUST TO KEEP CONVECTION ACTIVE W OF THE CENTER.
OTHER SYSTEMS...
A BAND OF SHOWERS AND THUNDERSTORMS IS FOUND WNW OF WAKE ISLAND,
WITH ANOTHER BAND E OF WAKE. THESE TWO BANDS ARE THE REMNANTS OF
INFLOW INTO WHAT IS LEFT OF TD 13W AND 15W. AS BOTH TDS CONTINUE TO
WEAKEN, THESE BANDS OF CONVECTION WILL GRADUALLY DECREASE.
CRUZ/KLEESCHULTE
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