834
FXPQ50 PGUM 190757
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
557 PM ChST Sun Jan 19 2025

.Marianas Synopsis...
Skies are mostly clear across the Marianas this afternoon. A shallow
trade-wind trough is located just southeast of Guam, focusing isolated
to scattered showers south of the forecast zones. The weakening
remnants of a shear line are seen over the far northern Marianas,
with patchy showers and cloudiness north of Agrihan. Scatterometry
shows fresh trade winds north of the boundary. To the south,
scatterometry and surface observations show moderate trade winds
across the region with some higher gusts seen on Guam, due to outflow
from showers to the southeast.

&&

.Discussion...
There was little change to the zone forecast. PoPs were increased to
20% for Guam and Rota for tonight as a shallow trough passes south
of the Marianas, and left at 10% for Saipan and Tinian with mostly
clear conditions upstream. Only isolated showers are expected
throughout the forecast period as a dry trade wind pattern prevails
across the region. The marine and surf forecasts are the main
concern as a pulse of north swell moves south through the CNMI,
discussed below.

&&

.Marine...
Latest buoy and altimetry data show combined seas of around 5 to 8
feet near the Marianas. There is a pulse of north swell moving south
across the far northern Marianas associated with a decaying shear
line. Altimetry shows sea heights of 10 to 13 feet near Agrihan
northward to around 22N. Model guidance shows the north swell
arriving tonight into early Monday morning, and a High Surf Advisory
and High Rip Current Risk were issued for north facing reefs through
Monday afternoon. Models are running lower than observed sea heights,
but the north swell looks to dissipate quickly as it arrives. Winds
are expected to be gentle to moderate for much of the forecast
period, becoming moderate to fresh around Thursday. A pulse of
increased trade swell and slightly higher north swell will arrive
around this time, increasing seas by a foot or so late in the week.

&&

.Eastern Micronesia...
No major changes from yesterday`s forecast. A dry trade-wind pattern
looks to continue through Monday night as the trade surge continues
to weaken. By Tuesday, a weak convergence band, possibly a developing
Inter-Tropical Convergence Zone (ITCZ), develops across the region.
At the same time, another strong mid-latitude high pressure system
moving eastward, well north of Micronesia, will usher in another
trade-wind surge. The fresh to strong winds with this surge will help
keep the ITCZ farther south, keeping in the main band of convergence
and associated showers south of the forecast points. Higher POPs
(Probability of Precipitation) of around 40 to 50 percent will remain
south, though POPs are expected to reach around 30 percent at all
three forecast points and remain at that level for several days at
Pohnpei and Kosrae, with Majuro seeing the return of a dry trade-
wind pattern by the end of the week.

For the marine environment, the trade-wind surge continues to
dissipate as the high pressure system responsible for generating the
gradient continues to push eastward. This will result in a bit of a
decrease in winds across the region and winds could fall below Small
Craft Advisory levels for a brief time before another surge moves
into the region. This surge will result in a return of fresh to
strong winds across eastern Micronesia, with near-gale winds possible
at times. Both seas and winds are expected to subside by the end of
the week at Pohnpei and Kosrae, allowing the Small Craft Advisory to
expire. Surf will likely fall below hazardous levels at Pohnpei as
well, though surf is expected to remain hazardous a bit longer at
Kosrae. However, winds, seas and surf look to remain elevated at
Majuro for a bit longer, possibly requiring the Small Craft Advisory
and High Surf Advisory to be extended.

&&

.Western Micronesia...
A series of weak trade-wind troughs are generating patchy showers
across the region. Yap and Palau will continue to expect periods of
scattered showers this upcoming week with the passage of trade-wind
troughs. Chuuk, however, will see a better chance of showers and
thunderstorms starting around midweek due to the proximity of a
convergence zone building south of Chuuk at that time. Models show
embedded troughs that may spread showers north over Chuuk, possibly
making showers numerous at times.

Buoy and altimetry data show seas of 5 to 8 feet this afternoon,
composed of dominant east swell. Pulses of north swell are expected
to add to surf heights for Palau and Yap, although swell magnitudes
are between 2 and 4 feet, with no hazardous surf conditions expected.
Trade swell is expected to increase another foot or two this week,
with the highest seas near Chuuk, reaching around 9 feet around
midweek. This, and moderate to fresh winds would make seas choppy,
nearing Small Craft Advisory conditions. In the upcoming days, an
advisory may be considered if models indicate worsening conditions.

&&

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

     High Surf Advisory until 4 PM ChST Monday for GUZ001.

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

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

Marianas Waters...None.
&&

$$

Marianas: DeCou
East Micronesia: Kleeschulte
West Micronesia: Cruz