FXPQ50 PGUM 261942

AFDGUM



Area Forecast Discussion

National Weather Service Tiyan GU

Issued by National Weather Service Honolulu HI

542 AM ChST Fri Jun 27 2025



.Marianas Update...

Showers have trended significantly downward across the Marianas

overnight, with radar showing some stratiform remnants over mainly 

Rota coastal waters and westward. Surface observations reveal mostly

gentle to moderate southeast flow across the islands, with frequent

fresh gusts over Guam. Overnight scatterometry shows a relatively 

narrow band of fresh southeast winds extending out from Guam and 

Rota toward the northwest. Given radar, satellite, and latest model 

trends, Probability of Precipitation (PoP) was decreased to 40% 

across the Marianas for today, but increased back up to 60% for Guam 

and Rota and 50% for Tinian and Saipan tonight, as Invest 97W helps 

maintain a moist, somewhat convergent southeast to south flow across 

the area as it moves further away. A wet pattern will continue 

through the weekend and a Flood Watch remains in effect through late 

Sunday night, but the potential for widespread heavy rainfall looks 

to be diminishing.



&&



.Marine Update...

There was little change in the overnight marine forecast. A gentler 

south to southeast flow will prevail across the Marianas through 

Saturday as Invest 97W, centered west of the Marianas near 16.0N

140.1E, shifts further away. Combined seas of 4 to 6 feet for Guam 

and Rota, and 5 to 7 feet for Tinian and Saipan, look to build late 

weekend into early next week as a monsoon swell begins to build into 

the region. This looks to be in response to another possible 

disturbance developing east of the Marianas, leading to a moderate to

fresh southwest flow, but there is still significant disagreement 

between models. ECMWFwave keeps the stronger monsoon swell energy 

just further west of the Marianas, which would instead maintain a 

steadier east to southeast swell through early next week.



&&



.Hydrology Update...

Yesterday's heavy, widespread showers led to rainfall totals of 5.37

inches recorded at the Guam International Airport. Showers have 

since greatly diminished across the Marianas overnight, but an 

overall wet pattern will continue over the next few days as Invest 

97W helps maintain a moist southeast to south flow across the 

islands. Another inch or two of rain is possible through the weekend

with locally heavy showers possible, but the threat for flooding

across the islands looks to be diminishing as 97W weakens. Residents

in the Marianas, especially those in flood-prone areas, should 

continue to monitor for updates.



&&



.Tropical systems Update...

Invest 97W is currently located near 16N140E, west of the Marianas.

97W is currently rated low by the Joint Typhoon Warning Center (JTWC), 

meaning that development into a significant tropical cyclone is 

unlikely within the next 24 hours. Moderate to deep convection is

occurring near the center and within the convergent southeasterly

flow to the southeast, with most of the convection focused west of

Guam coastal waters. 97W has shifted further west and north of the

Marianas with little discernible organization at the surface, and 

model trends have it developing slower and further to the northwest,

increasingly away from the Marianas.



&&



.Eastern Micronesia Update...

There was little change in the overnight update. An Intertropical 

Convergence Zone (ITCZ) disturbance has been flaring up just east of

Kosrae with moderate to deep convection building west-northwest over

the area. Meanwhile, a broad embedded trough within the ITCZ is

maintaining a band of showers over much of Pohnpei State further

west. For Majuro, satellite and GLD network data reveal showers and 

thunderstorms building nearby within a region of enhanced 

convergence. PoPs of 50 percent were maintained at Pohnpei and Kosrae

with 40 percent for Majuro today as these features gradually shift 

west through the area, with decreasing showers over the next few days

as the ITCZ dissipates. Gusty winds will be possible at times near

heavier showers, especially in the morning near Kosrae and Majuro.



Seas across the region remain a mixture of trade swell and 

southeasterly swell, with buoys showing combined seas of around 4 to 

6 feet for Pohnpei and Kosrae, increasing to around 7 feet further

east near Majuro.



&&



.Western Micronesia Update...

Little change to the forecast. A mostly gentle southwest monsoon flow

prevails across Palau and Yap, with isolated to scattered showers

across the region, mainly within an area of weak troughing near and

north of Yap Proper. Shower potential increases later in the weekend

as the monsoon pattern strengthens across far western Micronesia, to

the south of a slowly developing Invest 97W. This may lead to

moderate to fresh southwest flow by around Sunday, but in the

meantime, winds will be light to gentle, with 2 to 3 foot seas near

Palau and Yap. To the east, scattered to numerous showers are seen 

within an ITCZ disturbance centered north-northeast of Chuuk Lagoon.

This disturbance looks to maintain at least scattered showers near 

and north of Chuuk Lagoon over the next day or so before shifting 

further away to the north. 3 to 5 foot seas will continue near Chuuk 

for the next few days, decreasing slightly later in the weekend as

the trade swell diminishes slightly.



&&



.Prev discussion... /issued Issued by National Weather Service Honolulu HI/ 



Marianas Synopsis...

Satellite and radar are showing cloudy skies and numerous showers 

over the Marianas. Rainfall reports of 3 to 5+ inches were 

commonplace today. Nearby buoys are indicating seas of 4 to 6 feet.



Discussion...

Moist, convergent flow along the eastern edge of the monsoon trough 

and developing tropical disturbance (Invest 97W) will persist over 

the Marianas. Latest deterministic and ensemble model guidance have 

trended towards 97W developing slower and tracking further west of 

the Marianas. While this casts doubt on the potential for wind 

hazards, the continuing expectation is for a very wet period to 

continue through the weekend. High-end scattered to numerous showers 

and isolated thunderstorms are expected, with locally heavy downpours

possible. A Flood Watch remains in effect through Sunday night. Into

next week, models differ quite a bit, but the general trend is for a

monsoon flow to develop over the Marianas, with a increased chance 

of showers and thunderstorms continuing.



Marine...

Gentle to moderate winds for Guam and Rota tonight, and moderate to 

fresh for Tinian and Saipan, will diminish and become more southerly 

Friday. Through the weekend, a tropical disturbance, Invest 97W, is 

expected to develop west of the Marianas, bringing heavier showers 

the next few days. Combined seas of 3 to 6 feet for Guam and Rota and

4 to 7 feet for Tinian and Saipan, look to build late weekend into 

early next week as the monsoon swell builds into the region as 97W 

departs. Winds also look to become southwest moderate to fresh.



There will be a moderate risk of rip currents along east and south 

facing reefs of the Marianas for the next few days. Surf could rise 

along south and west facing reefs late weekend into early next week 

with the potential for an elevated southwest monsoon swell.



Hydrology...

The monsoon trough and developing tropical disturbance, Invest 97W, 

are expected to bring widespread showers through the weekend. 

Rainfall amounts today have totaled 3 to 5+ inches already. Total 

rainfall amounts of 5 to 10 inches are expected through the weekend, 

with locally heavy amounts possible, mainly across Guam and Rota. 

This rainfall is expected to produce minor flooding across the 

islands, with flash flooding possible in the areas of heavier 

rainfall. 

 

Residents in the Marianas, especially those in flood-prone areas, 

should monitor this developing weather pattern closely as advisories 

and warnings could be issued late this week. 



Tropical Systems...

Invest 97W is west of the Marianas, centered near 16N142E. 97W is 

currently rated low by the Joint Typhoon Warning Center (JTWC), 

meaning that development into a significant tropical cyclone (TC) is 

unlikely within the next 24 hours. Moderate to deep convection is 

occurring near the center and to the north and east where convergent 

southerly and easterly flow meet, including over the Marianas. Much 

uncertainty in the track and development of Invest 97W still 

persists, but latest deterministic and ensemble model guidance have 

trended towards 97W developing slower and tracking further west of 

the Marianas.



Eastern Micronesia...

The Inter-Tropical Convergence Zone (ITCZ) has drifted north over 

Pohnpei and Kosrae to just south of Majuro. Have increased showers 

coverage to numerous and locally heavy for Pohnpei and Kosrae 

tonight. Showers expected to increase in coverage for Majuro tonight 

as the ITCZ lifts north, but keep coverage scattered. Scattered 

showers and isolated thunderstorms are expected through Friday night 

with probability of precipitation (PoP) of 40 to 50 percent. Gusty 

winds will be possible at times near heavier showers. The ITCZ is 

expected to dissipate, and mainly isolated to low-end scattered 

showers are expected over the weekend. Showers and thunderstorm 

chances increase early next week as the ITCZ looks to re-establish 

itself over eastern Micronesia.



Regional seas will remain a mix of trade and SE swell. Seas will 

range between 4 and 6 feet for Pohnpei and Kosrae. Slightly higher 

trade swell is likely for well-exposed waters around Majuro, with 

seas up to 7 feet through Friday. Aside from some fresh winds tonight

at Majuro, winds will generally be gentle to moderate the next few 

days. Winds look to increase and become moderate to fresh beginning 

Sunday at Majuro and early next week for Kosrae and Pohnpei as the 

trade flow strengthens. Residents should be aware of the large tides 

the next several days due to the new moon phase despite the fact no 

notable swells are currently forecast.



Western Micronesia...

Chuuk remains under a surface trough serving as the boundary between

easterly trades to the east, and west to northwest flow to the west.

This feature will likely trigger bursts of showers and thunderstorms

at times through Friday night. Chuuk conditions will be quite 

changeable over the weekend into early next week as the broader 

synoptic pattern evolves in response to 97W as it lifts northwestward

the next few days, but generally lower coverage of showers and 

thunderstorms expected. Winds will be light to gentle. Seas 3 to 5 

feet look to decrease slightly by the weekend as the trade swell 

subsides.



Further west, modest monsoon flow will result in scattered showers 

(PoPs 30-40 percent) and isolated thunderstorms for Yap and Palau 

through Friday. Over the weekend into early next week, the west to 

southwest monsoon flow is expected to increase as the a potential 

tropical disturbance (Invest 97W) looks to develop west of the 

Marianas, but likely staying well north of Yap and Palau, with 

showers and thunderstorm potential trending higher. Seas of 2 to 3 

feet and light to gentle winds look to continue through the end of 

the work week. Winds and seas will trend up through the weekend into 

early next week as the monsoon flow increases. Moderate to fresh 

winds and seas of 4 to 6 feet are expected by the weekend. Surf also 

looks to rise along south and west facing reefs. Residents should be 

aware of the large tides the next several days due to the new moon 

phase.



&&



.GUM WATCHES/WARNINGS/ADVISORIES...

GU...Flood Watch through late Sunday night for GUZ001.



MP...Flood Watch through late Sunday night for MPZ001>003.



Marianas Waters...None.

&&



$$



Marianas Update: DeCou

East/West Micronesia Update: DeCou

Marianas: Slagle

Micronesia: Slagle

Tropical: Slagle

