FXPQ50 PGUM 250734

AFDGUM



Area Forecast Discussion

National Weather Service Tiyan GU

534 PM ChST Sat Oct 25 2025



.Marianas Synopsis...

Satellite imagery shows partly cloudy to mostly cloudy skies, with

the most cloud coverage over Guam and their coastal waters. Altimetry

shows 5 to 6 feet and the buoy data shows about 4 to 5 feet.



&&



.Discussion...

A surface trough and a Tropical Upper-Tropospheric Trough (TUTT) are

producing scattered showers and isolated thunderstorms over the 

Marianas. These showers are expected to remain over the islands for 

the remainder of the weekend as these two features gradually move 

westward into the Philippine Sea. Over the beginning of next week, 

passing trade-wind troughs are anticipated to bring periods of 

showers over the islands. Over the latter half of next week, model 

guidance suggests, that in eastern Yap State a tropical disturbance 

may start to develop. This may bring more showers and thunderstorms 

for the latter half of next week. 



&&



.Marine...

Not a lot of change is expected over the next several days. Combined

seas are expected to remain around 4 to 6 feet with gentle to 

moderate easterly winds through most of next week. There will be a 

moderate risk of rip currents along north and east facing reefs of 

the Marianas through much of next week. There will also be a moderate

risk of lightning through Sunday night, and again around the end of 

next week. 



&&



.Eastern Micronesia...

Short Term - Pohnpei:

Similar to the past two days, a nearby TUTT axis (just to the west of

Pohnpei), is interacting with embedded subtle troughs within the

Inter-Tropical Convergence Zone (ITCZ), allowing episodes of heavy

showers and isolated thunderstorms to continue this afternoon. This

looks to continue into the evening. However, as a "meso bubble" forms

(a rain-cooled area of higher pressure that often decreases shower 

and thunderstorm coverage due to it helping to stabilize the 

atmosphere), look for shower coverage to drop back to scattered 

coverage after midnight.



Short Term - Kosrae:

The southern "tail" subtle trough to your northeast will move

overhead after midnight tonight. This will allow surface convergence

to increase somewhat. Additionally, outflow boundaries from 

convection to your north to northwest may be lurking just offshore as

well. The collision of these features may allow for shower coverage 

to increase to scattered after midnight.



Otherwise, the main theme going into next week will be for ITCZ to

become more energetic from 165E to the Date Line, with current 

upstream troughs (currently east of the Date Line) expected to become

better defined (show increased surface convergence), allowing for 

moisture to pool along them. This would then in turn allow for an 

increase of shower and thunderstorm coverage, which surges westward 

across all of eastern Micronesia. As such, the forecast has scattered

shower coverage (chance probabilities of 25-54%) in the forecast, 

and this looks good.



For our mariners, outside of locally higher gusts near heavier

showers and thunderstorms, you can expect mainly light to gentle

winds the next few days. However, as the aforementioned troughs move

in towards the middle of next week, winds may become gentle to 

moderate. Seas look to remain in the 4 to 6 foot range through the 

period.



&&



.Western Micronesia...

A surge in the westernmost extent of the ITCZ is expected to bring

periods of heavier showers, thunderstorms, and stronger winds to

Palau and Yap beginning tonight, to then peak Monday and Monday 

night. More pulses in the ITCZ are then going to bring on- and- off 

showers with some thunderstorms for several days after. This deep 

convection is expected to weaken and dissipate thereafter, but an 

already unstable environment will likely favor tropical disturbance 

development in eastern Yap State, especially in the second half of 

next week. As conditions remain highly uncertain at this time, kept a

generally wetter pattern in the forecast continuing from Tuesday.



Combined seas of 4 to 6 feet are expected to taper down by a foot or

two in Palau, Yap and Chuuk waters by the middle of next week, once

the dominant trade swell continues to diminish.



&&



.GUM WATCHES/WARNINGS/ADVISORIES...

GU...None.

MP...None.

Marianas Waters...None.

&&



$$



Marianas: Bowsher

East Micronesia: Doll

West Micronesia: Montvila