559
FXPQ50 PGUM 050719
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
519 PM ChST Sat Jul 5 2025

.Marianas Synopsis...
Satellite and radar imagery are showing partly to mostly cloudy
skies and isolated to low-end scattered showers. A few island-effect
showers are occurring along the leeward side of Guam. Local buoys
are indicating seas of 2 to 4 feet.

&&

.Discussion...
Light to gentle southerly flow around a surface ridge, along with
ample moisture (precipitable water values of 2.25" and higher), has
brought slow-moving and locally heavy showers across the Marianas.
Expect mainly isolated showers for tonight. Based off the island-
effect showers along the leeward side of Guam this afternoon,
confidence is increasing for island-effect convection on Sunday, and
possibly Monday, as the moisture profile trends up and winds become
lighter and more parallel to the islands from the south-southwest.
Have increased coverage to 40 percent and introduced locally heavy
downpours for the Marianas for Sunday. As we head into next week, the
ridge will shift further southeast, with the south to southwest
monsoon flow increasing and bringing an elevated potential for
showers and thunderstorms.

&&

.Marine/Surf...
Mainly light winds from the south tonight, then veering to southwest
Sunday and to westerly Sunday night. Winds will slowly pick up next
week as the high pressure ridge shifts east and the southerly
monsoon flow increases, with winds becoming gentle to moderate by
around Tuesday. Combined seas of 3 to 4 feet are expected through
Thursday, possibly increasing by around next weekend as a west-
northwest swell emanating from a distant tropical disturbance to our
northwest arrives.

A moderate risk of rip currents will continue along east facing
reefs through Sunday, becoming low Sunday night. A low risk will
persist along all other reefs. Surf and rip risk could rise by around
midweek along north and especially west facing reefs with the arrival
of the aforementioned west-northwest swell.

&&

.Eastern Micronesia...

.Short Term (Tonight through Sunday night)...

Kosrae:
The main items of interest are a pair of troughs, one moving through
Kosrae this tonight, and a fairly robust trough approaching Majuro
from the east. The initial Kosrae trough is less amplified and more
compact than its counterpart to the east, so we opted for just
scattered shower wording (50 percent probabilities), and with PWATs
near 2.4 inches (near seasonal values), any heavy rainfall should be
brief and isolated.

Then, heading into Sunday and Sunday night, showers increase to
numerous coverage as the Majuro trough moves overhead. This feature
will "pack more of a wallop", as PWATs on the latest MIMIC water
vapor loop are in the 3-3.25 inch range. Majuro caught a glancing
blow from this today, where 40 percent probabilities are in place. As
this feature moves into Kosrae by Sunday night, if later satellite
runs and water vapor imagery continue to show a similar pattern as
today, locally heavy rainfall may need to be added to the forecast
with rainfall probabilities increased further.

Majuro:
The afore-mentioned trough will continue to approach from the east,
passing overhead later tonight through the first half of Sunday. This
afternoon`s scatterometer pass did show convectively-augmented winds
up to 30 knots, as measured by the 2358Z observation of gusts to 28
knots. This occurred as convection collapsed upon itself and looks to
have been an isolated event. The analysis also shows the best surface
convergence bypassing you to the south, generally between 4N and 6N.
As such, scattered showers (30 to 40 percent probabilities) looks to
be all we can hope for, mainly late tonight or during the first half
of Sunday, as current imagery continues to show warming cloud top
temperatures.

Pohnpei:
You`ve been on the edge of high-end isolated to low-end scattered
shower coverage thus far, but this should improve tonight and
continue through Monday, as the effects of the approaching Kosrae
trough increases.

.Extended (Monday through Thursday)...
The models indicate a series of troughs will continue to move
westward in the trade flow, with rainfall probabilities highest near
any embedded troughs. This is fairly typical for this time of year,
and any rain-cooled temperatures or heavy rainfall is too difficult
to pinpoint this far out.

&&

.Western Micronesia...
Satellite imagery this afternoon reveals relatively quieter
conditions across far western Micronesia, with just isolated to
scattered showers and patchy cloud cover seen over Yap Proper and
Koror, with more extensive mid-to upper level cloud cover across the
southern Republic of Palau and southern Yap State. This is leftover
from prior convection associated with a broad, disorganized
convergence zone which has weakened and shifted to the southeast of
Yap and Palau since yesterday. A very weak monsoon-like trough
extends northeast over Koror and Yap Proper but there are few showers
associated with it, and model guidance shows this trough weakening
further as it shifts north of the area through the weekend. Quieter
conditions are expected for Yap and Palau through early next week as
a surface ridging pattern moves in behind the departing trough and
convergence area.

To the east, scattered showers are seen across Chuuk State,
associated with a broad north-south oriented trough extending into a
weak circulation developing to the south of Weno, just west of
Nukuoro Atoll in Pohnpei State. Latest model guidance points to this
disturbance shifting west into eastern Yap State and dissipating
over the next day or two. This disturbance will support scattered
showers for Chuuk through the weekend before quieter conditions set
up early next week.

Benign marine conditions continue across the region, with generally 2
to 3 foot combined seas for Palau and Yap, and 3 to 4 foot seas
expected for Chuuk. A pulse of slightly elevated southwest to west
swell looks to move into the Republic of Palau around midweek and
increase seas by a foot or so, mainly Wednesday through Thursday
night. This will accompany an increase to moderate to fresh southwest
monsoon flow, but otherwise, mostly gentle winds are expected
through the forecast period, out of the south to west for Palau and
Yap, and out of the northeast to southeast for Chuuk.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
MP...None.
Marianas Waters...None.
&&

$$

Marianas: Slagle
East Micronesia: Doll
West Micronesia: DeCou