417
FXPQ50 PGUM 091822
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
422 AM ChST Mon Mar 10 2025

.Marianas Update...
The latest model time heights due show some modest moistening
between ~10,000 and 20,000 feet, which could increase shower
coverage, intensity, duration somewhat. Otherwise, continue`d dry
conditions will prevail.

Of more concern is a northerly swell that arrives late Tuesday night
into Wednesday. The previous shift has this well covered in the
forecast though, so no significant forecast updates were needed
this morning.

&&

.Eastern Micronesia Update...
The forecast for east Micronesia remains status quo. Scattered
showers are seen off of Kwajalein`s radar, but these are north of
Majuro and isolated showers prevail across the rest of Micronesia.

No changes were made to the marine forecast. Minor coastal inundation
could impact Majuro later this week as a strong north-northeasterly
swell moves into the region.

&&

.Western Micronesia Update...
Little to no changes were made to the forecast. Satellite
observations show little to no shower activity across Chuuk and Yap
States. Scattered to numerous showers are seen well south of Palau
with some convective debris moving across Palau`s Coastal Waters.
Shower coverage is expected to remain isolated for all forecast
points today.

Marine conditions will remain benign with seas between 5 to 7 feet
across Palau and Yap and 6 to 8 feet across Chuuk. A larger
northerly swell may move into Yap and Chuuk later this week.

&&

.Prev discussion... /issued 514 PM ChST Sun Mar 9 2025/

Marianas Synopsis...
A dry trade-wind pattern continues across the Marianas, producing
moderate winds, with buoys reporting seas around 4 to 6 feet, and
satellite altimetry showing seas around 6 to 7 feet east and north
of the islands. Doppler Radar only shows some spotty, short-lived
showers traversing through the Marianas.

Discussion...
Dry weather is pretty entrenched across most of the region, and this
is unlikely to change this week. There is a weak shear line north of
the Mariana Islands, but on satellite it looks to be fragmenting.
Also due to the lack of moisture across the region, as satellite
derived precipitable water values are around 1.3 to 1.6 inches near
the Marianas and increasing slightly along the shear line, not
expecting any rain like what was experienced from the shear line at
the end of February. However, as the shear line fragment moves into
the northern islands, north of Saipan, winds will become more breezy
around Thursday.

Marine...
Moderate trades will prevail through Tuesday and then increasing to
moderate to fresh Wednesday as a weak shear line fragment moves into
the northern Mariana Islands, north of Saipan. Satellite altimetry
shows seas around 5 to 7 feet across the Marianas, but buoys on the
west side of the islands and being sheltered from the east swell,
such as Ritidian and Tanapag buoys, are reporting seas around 4 to 5
feet. Seas are expected to increase a foot or two Tuesday night,
before a significant north swell arrives Wednesday, potentially
leading to hazardous seas for small craft to develop. The increase in
north swell will also cause surf to build along north facing reefs,
with some wrap around to west and east reefs. This increase may cause
a high risk of rip currents to develop along north and east facing
reefs, along with high surf around 9 feet along north facing reefs.

Eastern Micronesia...
A dry trade-wind pattern remains entrenched across eastern Micronesia
today, with only spotty showers seen across the region. This looks to
continue for at least a couple more days. Latest model guidance
continues to show increasing showers across the region beginning
Tuesday night at Pohnpei and Wednesday at both Majuro and Kosrae. The
problem is that there doesn`t seem to be any mechanism moving into
the area to produce these showers. Guidance is showing POPs
(Probability of Precipitation) of up to 50 percent Thursday through
the weekend. Based on the high uncertainty of this convection,
decided to keep POPs at around 30 percent for now. If it begins to
look more promising for the convection to develop, POPs may be
increased in later forecasts.

A trade-wind surge looks to maintain large trade swell through
Monday. This surge stretches from Hawaii westward to near 152E.
Majuro can expect to see combined seas of up to 11 feet tonight and
10 feet Monday. Altimetry data supports this as it currently shows
seas of 9 to 11 feet to the east of Majuro, along with fresh winds
with strong gusts. The surge will weaken as the mid-latitude high
pressure system responsible continues to move east, away from the
area. This will allow winds and seas to subside across the area. The
trade swell will also continue to produce hazardous surf along east
facing reefs of Kosrae. With the trade swell expected to remain
at around 6 to 8 feet through Wednesday night, decided to extend the
High Surf Advisory through early Thursday morning.

Western Micronesia...
A dry trade-wind pattern stretches across the region this afternoon.
The MIMIC TPW product shows satellite-derived precipitable water
values have dropped below 2 inches at Palau, between 1.50 to 1.80
inches from there and farther west across Yap and Chuuk. An area of
trade- wind convergence remains to the south and continues to bring
scattered to numerous showers across open waters of southern Yap and
Chuuk State. As regional winds shift northeast, this area of
unsettled weather is expected to remain farther south, near the
equator. Overall, quieter conditions are expected across the main
islands of Palau, Yap, and Chuuk over the next few days. In the
latter half of the week, model guidance shows a return to scattered
showers for Palau and Chuuk when trade-wind convergence or an ITCZ-
like fragment develops across the region.

Buoy and altimetry data reveal combined seas are 5 to 7 feet across
the region, comprised of easterly trade swell and background north
swell. Building north-northeast swell in the latter half of next
week is expected to increase seas to 7 to 9 feet. This, along with
moderate to fresh trade winds over the next several days, would trend
towards choppier seas by late next week, however, latest wave models
do not indicate hazardous conditions for small craft at this time.

&&

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

$$

Marianas Update: Doll
East/West Micronesia Update: Williams
Marianas: Schank
East Micronesia: Kleeschulte
West Micronesia: Cruz