576
FXPQ50 PGUM 080744
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
544 PM CHST MON SEP 8 2025
MARIANAS SYNOPSIS
A FEW SHOWERS AND THUNDERSTORMS CONTINUE NEAR GUAM THIS EVENING, BUT
THEY'RE ON A DIMINISHING TREND. WINDS REMAIN LIGHT TO GENTLE, WITH
SEAS OF 3 TO 4 FEET. THE LATEST WATER TEMPERATURE AT THE IPAN BUOY IS
86 DEGREES.
DISCUSSION
A FAIRLY TYPICAL WET SEASON PATTERN IS IN PLACE, WITH LIGHT TO GENTLE
WINDS HELPING TO DEVELOP ISLAND CONVECTION NEAR THE WESTERN
COASTLINES. WINDS ARE SLIGHTLY HIGHER DURING THE LATE MORNING AND
AFTERNOON AT HIGHER ELEVATIONS, BUT HERE TOO THEY'VE BEEN LESS THAN
WHAT WE'D TYPICALLY SEE. OVERALL, A SIMILAR PATTERN WILL CONTINUE
THIS WEEK WITH STREAMLINE ANALYSIS CONFIRMING WHAT THE MODELS SHOW,
THAT NO SIGNIFICANT SURFACE TROUGHS ARE EXPECTED TO INFLUENCE OUR
WEATHER THIS WEEK. HOWEVER, UPPER-LEVEL DIVERGENCE FROM A TROPICAL
UPPER TROPOSPHERIC TROUGH (TUTT) CELL, ACROSSING THE NORTHERN
MARIANA ISLANDS THE NEXT FEW DAYS, WILL HELP TO SUPPORT ISOLATED
THUNDERSTORMS ACROSS THE MARIANAS, WITH MORE ISLAND CONVECTION DURING
THE LATE MORNING AND AFTERNOON HOURS, IF THE WINDS CAN REMAIN UNDER
10 KNOTS. MODELS SUPPORT EASTERLY WINDS AROUND 6 TO 9 KNOTS DURING
THE LATE MORNING AND AFTERNOON HOURS, WHICH IS SUFFICIENTLY LIGHT FOR
THE CONVECTION TO DEVELOP. HOWEVER, ANY ISLAND CONVECTION WILL BE
TIED TO THE IMMEDIATE WESTERN COASTLINES, ESPECIALLY NEAR GUAM (DUE
TO BETTER OROGRAPHICS), AND MORE SO TO THE WESTERN COASTAL WATERS. AS
SUCH, MID TO HIGH-LEVEL CLOUDS FROM CONVECTIVE BLOWOFF TO THE SOUTH
OF THE MARIANAS COULD HINDER THIS POTENTIAL. AS SUCH, WE OPTED FOR
JUST ISOLATED SHOWER AND THUNDERSTORM COVERAGE FOR NOW, AND WILL MAKE
SHORT TERM ADJUSTMENTS (WITHIN THE NEXT 24 TO 48 HOURS) AS NEEDED,
WHICH COULD BE INSERTED INTO THE FORECAST DURING THE MIDNIGHT SHIFT
PACKAGE OR WITH MORNING UPDATES.
MARINE
ASIDE FROM CONVECTIVELY-DRIVEN WIND GUSTS POTENTIALLY DEVELOPING
NEAR WESTERN COASTLINES, MARINERS CAN EXPECT LIGHT TO GENTLE WINDS
WITH SEAS HOLDING IN THE 3 TO 4 FOOT RANGE THIS WEEK.
EASTERN MICRONESIA
THE INTER-TROPICAL CONVERGENCE ZONE (ITCZ) STRENGTHENED ACROSS THE
REGION AS EXPECTED. HOWEVER, CONVECTION IS LIMITED ACROSS THE REGION.
THIS IS LIKELY DUE TO THE LOSS OF THE UPPER-LEVEL DIVERGENCE THAT WAS
HELPING THE CONVECTION YESTERDAY. THE UPPER DIVERGENCE IS NOW FOUND
TO THE NORTHEAST OF MAJURO, WHERE IT IS INTERACTING WITH THE ITCZ AND
AN EAST-NORTHEAST ORIENTED TRADE-WIND TROUGH TO PRODUCE SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS. THE DIVERGENCE LOOKS TO CONTINUE
TO WEAKEN OVER THE AREA WHILE THE ITCZ IS EXPECTED TO CONTINUE TO
STRENGTHEN WESTWARD. MEANWHILE, THE TRADE-WIND TROUGH WILL ALSO MOVE
WEST. THESE TWO FEATURES WILL HELP TO INCREASE CONVECTION ACROSS THE
REGION. KOSRAE AND MAJURO WILL SEE INCREASED SHOWERS LATE TONIGHT,
AFTER MIDNIGHT, WITH POHNPEI SEEING THE INCREASED CONVECTION TUESDAY.
LATEST GUIDANCE NOW SHOWS LESS RAINFALL AND SHOWER COVERAGE THAN
PREVIOUS RUNS, WITH THE ITCZ PUSHING NORTHWARD A BIT EARLIER. THIS
SCENARIO LOOKS MORE REASONABLE. THEREFORE, LOWERED POPS (PROBABILITY
OF PRECIPITATION) TO THE 50% RANGE. A DRY TRADE-WIND PATTERN IS THEN
EXPECTED TO RETURN AROUND THURSDAY AND CONTINUE INTO THE WEEKEND.
BENIGN MARINE CONDITIONS WILL CONTINUE INTO THE WEEKEND, WITH
COMBINED SEAS OF 5 FEET OR LESS AND LIGHT TO GENTLE WINDS THROUGH
THE PERIOD.
WESTERN MICRONESIA
A LIGHT WIND PATTERN EXTENDS OVER PALAU AND YAP, WHICH HELPED TO
INITIATE ISLAND-EFFECT THUNDERSTORMS JUST OFF THE WESTERN SHORES OF
BABELDAOB ISLAND IN PALAU EARLIER THIS AFTERNOON. AS THE SUN SETS,
ISLAND-EFFECT CONVECTION WILL END TO DUE TO THE LACK OF HEATING OF
THE ISLANDS, SO A FAIRLY DRY NIGHT IS EXPECTED FOR BOTH PALAU AND
YAP. THERE IS A WEAK SURFACE TROUGH TO THE SOUTH-SOUTHWEST OF THE
MARIANAS THAT IS GENERATING SCATTERED SHOWERS ACROSS THE OUTER
ISLANDS OF YAP STATE, BUT IS NOT EXPECTED TO MOVE INTO YAP PROPER
UNTIL DURING THE DAY TUESDAY. WINDS WILL REMAIN LIGHT AND POTENTIALLY
VARIABLE AT PALAU TUESDAY, POTENTIALLY LEADING TO ANOTHER ROUND OF
ISLAND-EFFECT CONVECTION THAT MAY STAY OVER THE LARGER ISLAND OF
BABELDAOB DURING THE LATE MORNING AND AFTERNOON HOURS, SO MENTIONED
SCATTERED SHOWERS FOR THE AFTERNOON HOURS OF TUESDAY IN THE FORECAST
AND KEPT THE POTENTIAL FOR ISOLATED THUNDERSTORMS THROUGH THE DAY.
OTHERWISE, FAIRLY QUIET WEATHER IS EXPECTED TUESDAY NIGHT AND INTO
WEDNESDAY. AROUND WEDNESDAY NIGHT OR THURSDAY, MODELS CONTINUE TO
SUPPORT THAT AN ITCZ FRAGMENT OR A SURFACE TROUGH BREAKING OFF OF THE
ITCZ IN EASTERN MICRONESIA WILL MOVE INTO YAP AND PALAU, INCREASING
THE POTENTIAL SHOWERS AND THUNDERSTORMS THROUGH FRIDAY TO AROUND 30%
TO 40%.
OVER BY CHUUK, SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
PASSING THROUGH THIS EVENING, DEVELOPING ALONG WEAK CONVERGENT FLOW
AND TRADE-WIND TROUGHS MOVING THROUGH THE STATE, WHILE CONVECTION
ALONG THE ITCZ IN EASTERN MICRONESIA HAS BECOME RATHER FRAGMENTED
SINCE YESTERDAY. BASED ON MODEL GUIDANCE, KEPT THE POTENTIAL FOR
SHOWERS AROUND 50% TONIGHT, BUT DECREASED THE POTENTIAL FOR TUESDAY
TO 40% AS THE BULK OF THE SHOWERS MAY SHIFT WESTWARD FASTER THAN
PREVIOUSLY EXPECTED. THE ITCZ IS STILL EXPECTED TO LIFT NORTHWARD AND
DECREASE THE POTENTIAL FOR SHOWERS TO AROUND 30% ACROSS CHUUK STATE
TUESDAY NIGHT TROUGH FRIDAY, WITH ISOLATED SHOWERS EXPECTED
SATURDAY.
ALTIMETRY DATA EARLIER TODAY SHOWS BENIGN SEAS OF 2 TO 3 FEET NEAR
YAP AND PALAU AND 3 TO 4 FEET NEAR CHUUK. COMBINED SEAS ARE EXPECTED
TO INCREASE TO 3 TO 5 FEET AROUND WEDNESDAY AND THURSDAY WHEN A
PULSE OF NORTHERLY SWELL MOVES THROUGH THE REGION.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: DOLL
EAST MICRONESIA: KLEESCHULTE
WEST MICRONESIA: SCHANK
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