770
FXPQ50 PGUM 310852
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
652 PM ChST Fri Jan 31 2025

.Marianas Synopsis...
Dry and breezy trades dominate the region as a strong subtropical
ridge builds to the north. Skies are partly cloudy over the Marianas
with just a few isolated showers nearby, mainly to the north and west
of Tinian and Saipan. These are associated with a weak shear line
extending northeast to southwest across the northern CNMI, passing
over Anatahan and Alamagan. Scatterometry shows an area of sustained
winds up to around 30 mph north of the shear line, and at around 25
mph to the south, extending over the Marianas. Surface observations
across the islands reveal mostly fresh trade winds with frequent
strong gusts.

&&

.Discussion...
Fresh to strong east-northeast trades will continue through Saturday,
and begin to diminish on Sunday as a mid-latitude low digs into the
subtropical ridge to the north, passing east over southern Japan.
This will weaken the pressure gradient and subsequently the trade-
wind surge that is currently underway, allowing winds to diminish
to moderate to fresh early next week. Wind direction will veer from
east-northeast to east-southeast briefly around Monday as low-
pressure shifts eastward to far north of the CNMI, which could
slightly increase surface convergence at times. However, showers are
expected to remain isolated throughout the forecast period, with
slightly higher chances near Saipan and Tinian as the shear line to
the north lingers nearby. The main forecast concerns are in the
Marine and Surf section as surging trade winds maintain hazardous sea
conditions and surf.

.Marine/Surf...
Buoys and altimetry show combined seas of 9 to 11 feet this
afternoon. Sea conditions are expected to remain hazardous through
the weekend as a trade wind surge builds eastward across the region,
following the area of high pressure north of the CNMI. Winds will
start to diminish Sunday, but seas will be slower to diminish.
During this time, surf will remain hazardous across north facing
reefs, and a high risk of rip currents will continue for north and
east facing reefs. The Small Craft Advisory, High Surf Advisory, and
High Risk of Rip Currents remain in effect through Sunday afternoon.

&&

.Eastern Micronesia...
Pohnpei: Locally heavy rainfall and wind gusts to 35 mph possible
tonight, as a fairly sharp and compact surface trough bisects Pohnpei
and Kosrae. This feature was the focus for intense convective
development at Kosrae earlier this morning, with the airport showing
a few hours of visibilities between 1/4 of a mile and 3 miles, which
often occurs with moderate (3 miles) to very heavy (1/4 to 1 1/2
mile) rain rates. This feature (the surface trough) is advecting rich
moisture northward, with the latest MIMIC water vapor imagery
showing PWATs (Precipitable Water values) of 2.7 to 3 inches.

Additionally, this afternoon`s scatterometer pass captured the
eastern half of this feature and sampled 20 to 25 knot winds. Things
will gradually taper off For Sunday into Monday precipitation-wise.
However, additional disturbances in the flow will allow for brief
periods of increased rainfall probabilities Monday and Thursday. As
such, we decided to hoist a short-fused Small Craft Advisory, valid
through 2 PM Saturday, to account for the higher winds mentioned in
the paragraph above.

Kosrae: the surface trough and attendant MCC (Mesoscale Convective
Complex) that developed overnight is continuing to push off to the
west-northwest away from your region. However, it`ll remain close
enough to produce higher wind waves through the first half of
tonight, as well as increased northerly swell from a decaying shear
line to your north between 10N and 11N.

Majuro: A surface trough to your southeast is the leading edge of
some enhanced trade convergence and it`s allowing a localized area of
mostly cloudy skies and scattered showers to develop. All of this
looks to pass off to your south, but close enough for scattered
showers to be in the forecast Saturday and Saturday night. Otherwise,
look for isolated showers to prevail.

Attention then turns to a significant increase in sea heights, as
another shear line drops south, but remains to the north of eastern
Micronesia while bisecting the northern third of the FSM from it`s
remainder to the south. This looks to occur by the middle of next
week (in terms of shear line positioning). However, this feature and
an area of high pressure translating east across the central Pacific
will allow the pressure gradient to tighten in the Monday through
Wednesday time frame. Increased swell and seas will pose a concern
for hazardous conditions for surf and to small craft if the current
model forecast trends remain.

&&

.Western Micronesia...
A trade-wind surge is producing a wide swath of elevated winds across
the region, with pulses of convective clusters hugging the Equator the
next several days, producing drier conditions across much of western
Micronesia. Palau, Yap, and Chuuk will continue to see isolated to
low-end scattered showers the next few days, followed by a northward
shift in the convergence zone; this will allow more on-and-off
showers to make their way across in the first half of next week.

A combination of strengthening trade swell, significant north swell,
and elevated wind waves are producing sea conditions hazardous to
small craft, with 8 to 12 foot seas to persist into the weekend. As
such, a Small Craft Advisory remains valid from through late Saturday
afternoon. These conditions may persist a few days longer at Palau
and Yap, so the Small Craft Advisory may be extended if conditions
warrant. The same swells are producing hazardous surf along north
facing reefs of Palau and Yap, so a High Surf Advisory remains valid
through Saturday afternoon as well. There is some chance that
hazardous surf may persist along said reefs a little longer, so a
High Surf Advisory may be extended if conditions warrant. High
uncertainty remains in potential hazardous surf along north facing
reefs of Chuuk, so conditions will be monitored for any possible
changes the next few days.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through Sunday afternoon for GUZ001.

     High Surf Advisory until 4 PM ChST Sunday for GUZ001.

MP...High Rip Current Risk through Sunday afternoon for MPZ001>003.

     High Surf Advisory until 4 PM ChST Sunday for MPZ001>003.

Marianas Waters...Small Craft Advisory until 4 PM ChST Sunday for PMZ151>154.

&&

$$

Marianas: DeCou
East Micronesia: Doll
West Micronesia: Montvila