649
FXPQ50 PGUM 251916
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
516 AM ChST Sat Apr 26 2025

.Marianas Update...
Quiet weather continues across the Marianas with little change in
this forecast package. Radar reveals small isolated showers moving
west-southwest through the area early this morning, with slightly
higher coverage around and south of Guam where there may be a bit of
surface wind-speed convergence as evidenced by the overnight
scatterometry. Gentle to moderate trades persist across the region
for today and are expected to continue through the forecast period.
PWATs range 1.6 to 1.8 inches over the Marianas, and there is a
broad area of higher PWATs around 2 inches just north and east of
Saipan coastal waters. This increased moisture looks to move in
tonight with the arrival of a weak surface trough, bringing low-end
scattered showers (30 percent chance) through the latter part of the
weekend.

Local buoys indicate combined seas of 4 to 6 feet, which are
expected to continue through at least early next week. A moderate
risk of rip currents is expected along north and east facing reefs
through the weekend. The secondary north swell will begin to taper
down late Sunday, which may allow the rip current risk to fall to low
along north facing reefs as early as Monday.

&&

.Fire weather...
0.08 inches of rain fell at the Guam International Airport yesterday,
and there has been no wetting rainfall of 0.20 inches or greater
within the last week. This allowed the KBDI to continue increasing
slightly with today`s reading at 680, which is in the high category.
Gentle to moderate trade winds will continue with occasional fresh
gusts in the afternoon, and are expected to remain below critical Red
Flag criteria. However, fire danger remains elevated, especially at
higher terrain where stronger winds are expected. Afternoon relative
humidity values will continue to fall near or below 60 percent. A
weak trough will bring higher rainfall amounts tonight and Sunday,
but a wetting rain is not expected so the KBDI may continue to rise
over the next few days.

&&

.Eastern Micronesia Update...
No significant changes were made given a void of any significant
features. Northeast trades will persist with rainfall potential
starting to look less in terms of coverage on tonight`s model runs,
showing low-end scattered coverage (30 percent probabilities, if
that). Didn`t want to go "whole hog in" on that though, and opted to
trend lower on rainfall potential while maintaining scattered
showers for Pohnpei and Kosrae. For Majuro, the biggest change was to
bring thunder in earlier based on new ECMWF convective parameters.

&&

.Western Micronesia Update...
Palau and Yap:
Here too no significant changes were made this update, with emphasis
using the GEFS for winds as the operational GFS and ECMWF continue
to show a slowly-developing system will take place Sunday night
through the middle of the week, possibly bringing some heavy rainfall
to Palau or Yap. There`s still plenty of considerations up in the
air though, so we`ll continue to monitor things while coordinating
with the Joint Typhoon Warning Center (JTWC). Stay tuned!

Chuuk:
No significant changes were made as the forecast remains on track
with model guidance and the previous forecaster thinking. In general,
scattered showers and isolated thunderstorms remain in your picture
for at least the next 48 hours, possibly longer.

&&

.Prev discussion... /issued 558 PM ChST Fri Apr 25 2025/

Marianas Synopsis...
Gentle to moderate trades prevail. Satellite imagery and Doppler
Radar indicate run-of-the-mill trades making their way across the
region. Buoys and altimetry indicate seas are 4 to 5 feet.

Discussion...
Mostly dry conditions will be followed by a brief period of low-end
scattered showers brought by a passing minor trough later in the
weekend. After, a drier regime will return as most of the convection
in the region remains south of the Marianas.

Marine...
Combined seas of 4 to 6 feet are expected to remain as such at least
into early next week. A moderate risk of rip currents is expected
along north and east facing reefs for at least the next several days.
As secondary north swell begins to taper down late Sunday, rip
current risk may fall back to low along north facing reefs as early
as Monday.

Fire weather...
So far today, 0.04 inches of rain has fallen since midnight, with no
significant rainfall expected until midnight. As such, the KBDI is
expected to increase further, which is at 675 currently (high
category). A minor trough will bringer higher rainfall amounts over
the weekend, but not likely to be wetting rains, so the KBDI may
continue to creep upwards. Even so, winds are expected to remain
gentle to moderate, so conditions critical to fire weather are not
expected at least over the next few days.

Eastern Micronesia...
A much drier pattern is in place across eastern Micronesia than what
is favored by the models. There is a very weak band of trade-wind
convergence evident on the latest ASCAT analysis and satellite data
stretching east across Pohnpei to just north of Kosrae, ending west
of Majuro. Convection looks to increase through the evening along
this band for both Kosrae and Pohnpei as very weak troughs move
through the region, interacting with the convergence. Model guidance
is favoring a large increase in convection, with numerous showers
showing up on the GFS and ECMWF across Pohnpei and Kosrae. However,
this does not appear likely as the convergence and troughs will
remain poorly organized. Based on a large degree of uncertainty with
the convective development across the area, maintained scattered
showers through the weekend and through the end of the coming week.
Showers look to remain isolated across Majuro through Saturday night
before a more pronounced trough moves in from east of the Date Line,
helping to increase convergence across the Marshalls. It does appear
likely that the strongest convection will be early next week for
Majuro and around midweek for Kosrae, with the bulk of the convection
remaining just south of Pohnpei. Majuro does look to dry out again
near the middle of next week.

Other than showers and thunderstorms, conditions look to stay
relatively benign across the marine environment through the middle of
next week. For Pohnpei and Kosrae, expect gentle to moderate trade
winds through the period. For Majuro, the difference is a brief
period of occasionally fresh winds early next week. Seas are
expected to remain at or below 7 feet across the region through the
period. There is, however, a possibility that a northeast swell could
build high enough to produce hazardous surf conditions along north
facing reefs of Pohnpei, and north and east facing reefs of Kosrae
over the weekend. The night shift will need to take a closer look to
see if the swell will be enough of a northerly component to produce 9
foot surf along north facing reefs at both locations. If the swell
remains more of an easterly component, hazardous surf can be expected
for east facing reefs of Kosrae, due to the lower threshold for
hazardous surf.

Western Micronesia...
The circulation embedded in the Near-Equatorial Trough (NET) is now
designated 99W by JTWC, currently rated as sub-low for development.
Afternoon scatterometry data shows the circulation near 4N133E with
visible satellite imagery continuing to show the deeper convection
within the moist westerly flow, focused along the southern portion
of the circulation and NET. A northward shift of the NET is expected
over the weekend and early next week, while the 99W meanders
northwestward as a broad circulation. The potential for some
development is there, but not for another few days, so will continue
to monitor in the coming days. With its current track, it should
pass well west of the main islands of Palau, but will still be in a
good spot to steer moist southwesterlies towards the islands. Went
ahead and added the potential for locally heavy showers and gusts
with heavier showers late weekend and early next week, but continue
to monitor forecasts as timing and intensity of convection may shift
with subsequent model runs. Yap Proper will also see a trend towards
more unsettled weather, but ensemble models show the bulk of activity
near, but mainly southwest of the island at this time. For Chuuk,
moderate convergence behind a broad trough to the west is expected to
maintain scattered showers and isolated thunderstorms over the next
day or so, then a northward shift of the NET and possibly the
development of another embedded, weak disturbance will also increase
convergence across central Micronesia over the weekend and through
the middle of next week, maintaining scattered showers across Chuuk.

Benign marine conditions continue over the next several days with
combined seas of 3 to 5 feet expected, comprised of minor trade swell
and wind waves. A longer-period north swell reaches the region over
the weekend; this may slightly add to seas, but would mainly boost
surf along north-facing reefs. Neither seas nor surf are expected to
reach hazardous levels at this time. Winds will be gentle to
moderate, but fresh gusts are possible with the unsettled weather
pattern developing in far western Micronesia late weekend and early
next week.

&&

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

$$

Marianas Update: DeCou
East/West Micronesia Update: Doll
Marianas: Montvila
East Micronesia: Kleeschulte
West Micronesia: Cruz