225
FXPQ50 PGUM 031844
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
444 AM ChST Fri Apr 4 2025

.Marianas Update...
A High Risk of Rip Currents Statement remains in effect.

Only minor edits were needed to the forecast tonight. The northeast
swell appears to be a little sluggish in moving into region. The surf
lower-end was dropped a little to reflect this. Altimetry shows seas
of 5 to 7 feet, Ipan and Ritidian Buoys in the region are suggesting
5 to 7 feet surf and Tanapag showing 7 to 9 feet surf. Weather-wise
a few week troughs may push through the region. This will make the
difference between 10 percent and 20 percent chance of showers over
the next week.

&&

.Eastern Micronesia Update...
Majuro:
Things have quieted down since yesterday`s downburst at Majuro, where
the National Weather Service Office rerecorded 2.76 inches of
rainfall, with the downburst having inflicted some damage to roofs as
well. The trough responsible for "yesterday`s action" was a subtle
little feature that developed, and its currently stretching from just
west of Kwajalein to east of Kosrae. Have no fear though, another
trough approaching Majuro from the east is forecast to move overhead
later this evening and tonight, with modest divergence aloft helping
increase lift and storm-top ventilation. This will help keep the
clouds socked in there with off-and-on showers through the night,
with a few thunderstorms mixed in as well.

Kosrae:
An area of enhanced surface convergence is positioned halfway between
you and Pohnpei, which is what helped focus yesterdays shower and
thunderstorm activity. As this feature continues to move off to the
west, the incoming trough will help keep abundant cloud cover across
the area, with scattered showers and a thunderstorm or two developing
today and tonight, before possibly getting a break in the action
Saturday.

Pohnpei:
You too are sandwiched between another subtle trough departing the
area as it heads towards Chuuk, and the surface convergence mentioned
above approaching you from the southeast. Although the best
convergence remains south of you through Saturday morning, it`ll be
close enough to keep at least mostly cloudy skies and scattered
showers in your forecast. A stray thunderstorm can`t be ruled out
either.

&&

.Western Micronesia Update...
Palau and Yap:
The Joint Typhoon Warning Center (JTWC) is watching an area of
disturbed weather (no Invest has been assigned yet) near 2N130E, or
to the west-southwest of Helen`s Reef. The midnight scatterometer
analysis (surface) and 925 mb (~1500 feet AGL - Above Ground Level)
both indicate two areas of circulation. We agree with JTWC that the
GFS is likely onto something as it develops a weak system that heads
off towards Mindanao, Philippines. As it does so, it`ll swing a Near-
Equatorial Trough (NET) northward as it straddles northern Palau and
Yap along the southern shores. With this in mind, we maintained
scattered showers and isolated thunderstorms for Palau while
increasing cloud cover and rainfall potential at Yap, especially
tonight into Saturday.

Chuuk:
Cloud cover and rainfall potential will be on the increase the next
24 hours, as a subtle surface trough departing Pohnpei moves
overhead, acting as a focus for increasing shower and thunderstorm
development. After this feature passes by, additional disturbances in
the flow will keep your weather unsettled for the start of next
week.

&&

.Prev discussion... /issued 647 PM ChST Thu Apr 3 2025/

Marianas Synopsis...
Himawari visible satellite shows isolated showers and partly cloudy
skies over the Marianas. Surface observations continue to show
moderate wind speeds with occasional fresh gusts across the area. A
line of light showers is seen east of Guam and Rota, extending
partially into Rota coastal waters.

Discussion...
Scattered showers briefly crossed Saipan and Tinian coastal waters
this morning, associated with a weak surface trough now west of the
Marianas. The next, weaker trough looks to move in late tonight, but
satellite-derived precipitable water (PWAT) imagery shows much drier
air moving in ahead of the next round of light showers, and only
isolated coverage is expected. The far northern CNMI will see the
largest increase in showers overnight, but this is still a very
modest, transient feature. Model guidance and satellite trends
indicate the Marianas will continue to see somewhat of a north-south
moisture gradient for the next day or two as subtle trade-wind
troughs cross the area, mainly through the northern CNMI. One such
feature may bring another round of scattered showers near Tinian and
Saipan Friday night. Thereafter, only isolated showers are expected
through the forecast period as a mild trade-wind pattern persists.

Marine...
Nearby buoys and altimetry indicate combined seas of 5 to 7 feet. A
pulse of long-period northeast swell is beginning to move through the
region and may bump seas up by a foot or so through the end of the
week. Gentle to moderate trade winds are expected to continue through
the forecast period. The arrival of the long-period swell has led to
an increase in surf, producing a high risk of rip currents for east
facing reefs for the next few days, and maintaining the moderate rip
current risk for north reefs. Swells and corresponding surf are
expected to diminish this weekend into early next week, allowing the
rip current risk to drop as well around that time.

Fire weather...
Winds continue to steadily trend downward with gentle to moderate
speeds expected through the forecast period, but fire danger remains
high for Guam with dry conditions to continue. Fire danger will be
greater across higher terrain where wind speeds are typically higher.
No rain fell at the Guam International Airport yesterday, and the
KBDI (currently in the high category at 638) is expected to continue
to rise, with afternoon relative humidity values dropping below 60
percent. A wetting rain is not expected in the next several days.

Eastern Micronesia...
A trade-wind surge is dominating the weather in Eastern Micronesia.
It`s creating an area of scattered showers and isolated thunderstorms
with pockets of numerous showers along its southern and western
flanks, which happen to be near Pohnpei, Kosrae and Majuro. Just a
few hours ago an outflow boundary hit Majuro, causing a burst of
heavy rain and gusts of around 40 mph. Weather at Pohnpei and Kosrae
is expected to be subdued compared to that, but all 3 will be fairly
wet this week. Pohnpei will be scattered tonight, could be numerous
Friday through Saturday, then should be scattered Saturday night
through Monday, then could be drier Tuesday. Kosrae will be scattered
through Sunday, then drier Monday and Tuesday. Majuro will be
scattered through Saturday, drier Saturday night through Monday, then
scattered again on Tuesday. Winds will start to diminish after Sunday.

Pohnpei Waters will have winds of 10 to 15 knots, and seas starting
at 6 to 8 feet and diminishing to between 4 and 6 feet by Tuesday.
Overall, these will bring benign marine conditions for small craft.

Kosrae Waters will see winds of 15 to 20 knots with gusts to 25
knots through Sunday, which will then diminish to between 10 and 15
knots for Monday and Tuesday. Seas of 7 to 9 feet will diminish to
between 4 and 6 feet by Monday, bringing challenging conditions at
first which will become benign over the weekend.

Majuro Waters will receive winds of 15 to 20 knots with gusts to 25
knots through Monday, then winds will diminish to between 10 and 15
knots on Tuesday. Seas will be around 6 to 8 feet through Monday then
diminish to between 5 and 7 feet Tuesday. These will be challenging
conditions through Monday, becoming benign on Tuesday.

Western Micronesia...
The near-equatorial trough and buffer circulation, that has been
hugging the equator well south of Palau and Yap, continues to shift
westward and are now on the western edge of the region near 130E.
Trade-wind convergence northeast of these features, along with a
couple of embedded trade-wind troughs moving through the region, are
generating scattered showers and isolated thunderstorms across
Palau, the outer islands of Yap State and through Chuuk State, while
still remaining south of Yap Proper this evening. As the near-
equatorial trough and buffer circulation exit the region, the area
of trade-wind convergence will weaken but trade-wind troughs will
continue to support periods of scattered showers and isolated
thunderstorms across the region, even lifting showers northward into
Yap Proper as the trough currently moving into eastern Yap State
from Chuuk State passes near Yap Proper around Friday night and
Saturday.

Buoy and altimetry data continue to show seas of 4 to 6 feet near
Palau and Yap Proper, increasing to 6 to 8 feet around Chuuk State.
A pulse of long-period northeast swell is still moving towards Chuuk
State as drifting buoys north of Pohnpei show seas increasing
slightly to around 9 feet as the swell moves in. This swell will
cause surf heights along north and east facing reefs to build
overnight which are expected to peak Friday. Wave models show this
northeast swell peaking at a swell height of 4 feet with a period
around 12 to 14 seconds Friday. Surf will be elevated but expected to
remain below 12 feet for east-facing reefs and just below 9 feet for
north-facing reefs of Chuuk. If near the water, be careful as
currents will be strong along cuts in the reefs.

&&

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

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

Marianas Waters...None.
&&

$$

Marianas Update: Bowsher
East/West Micronesia Update: Doll
Marianas: DeCou
East Micronesia: Stanko
West Micronesia: Schank