140
FXPQ50 PGUM 161806
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
406 AM ChST Sat May 17 2025

.Marianas Update...
Little to no changes were made with this forecast package. Satellite
and doppler radar observations show isolated showers across the
region. The dry conditions will continue through the weekend, with
some hints at deeper moisture moving in early next week.

No changes were made to the Marine forecast. Benign seas are
expected to continue through the next several days.

&&

.Fire Weather...
0.03 inches of rain fell yesterday at the Guam International
Airport. This has allowed the KBDI to rise to 748, which is in the
high category due to winds falling below the 20 mph threshold. Both
winds and relative humidity values look to remain below Red Flag
Warning criteria the next few days. A wetting rain is not expected
for at least the next several days, and the KBDI is expected to
continue to rise.

&&

.Eastern Micronesia Update...
The main change was to increase rainfall today and tonight, as
convergence has settled very near Pohnpei, with the models suggesting
an increase in convective coverage tonight, aided by the nocturnal
increase that we typically see.

No significant changes were made for Kosrae and Majuro.

&&

.Western Micronesia Update...
The going forecast has things well in hand, with no significant
changes needed. In general, scattered showers and the occasional
thunderstorm will remain possible in Palau, with rainfall potential
decreasing from 50 percent today to 30 percent tonight.

For Yap, rainfall potential increases on Sunday, Finally, for Chuuk,
scattered showers today look to drop briefly to isolated coverage
tonight, before increasing back to scattered in coverage for your
Sunday, as convergence that weakens tonight, builds back cross the
area tomorrow.

&&

.Prev discussion... /issued 551 PM ChST Fri May 16 2025/

Marianas Synopsis...
Partly cloudy skies with isolated showers and gentle to moderate
trade winds reign over the region this afternoon. Buoys and
altimetry data show seas between 4 and 6 feet.

Discussion...
No major changes were made to the forecast. A dry trade-wind pattern
remains firmly intact across the Marianas. CIMMS MIMIC suggests the
Marianas has about 1.6 to 1.9 inches of Precipitable WATer (PWATs).
This is higher PWATs than previous weeks. Time heights also confirm a
deepening moisture layer, especially in the upper atmosphere and the
mid atmosphere by end of next week. These are the first signs that
the transition to wet season may be starting.

Marine...
Combined seas of 4 to 6 feet will keep marine conditions fairly
benign. Winds are expected to remain moderate through next week. A
moderate risk of rip currents remains along east facing reefs, with
a low risk along all other reefs.

Fire weather...
A trace of rain fell so far today at the Guam International Airport.
The KBDI remains at 745, which is in the high category due to winds
remaining below the 20 mph threshold. Both winds and relative
humidity values look to remain below Red Flag Warning criteria the
next few days. A wetting rain is not expected for at least the next
several days, and the KBDI is expected to continue to rise.

Eastern Micronesia...
A generally wet pattern produced by the ITCZ building overhead, is
expected to last for at least the next several days. A peak in
convective activity is expected over Pohnpei, with numerous heavy
showers, isolated thunderstorms and strong gusts expected Saturday,
with a slow taper down in shower coverage into early next week.
Patchy on-and-off showers are expected at Kosrae and Majuro for much
of the forecast period, with low-end scattered showers potentially as
early as Monday night.

Combined seas of 5 to 7 feet near Pohnpei and Kosrae, and 6 to 8 feet
near Majuro, are expected to taper down slowly to around 3 to 5 feet
by early next week, as trade swell and localized wind waves decrease.

Western Micronesia...
An unsettled weather pattern continues across far western and central
Micronesia, with strong convergent flow along the near-equatorial
trough (NET) just south of Palau, and increasing trade-wind
convergence over Chuuk State to the south of Chuuk Lagoon. Himawari
visible satellite imagery this afternoon shows scattered to numerous
showers over the Republic of Palau with the strongest convection
just south of Koror. These showers are expected to continue building
overnight through early tomorrow morning, before tapering back down
to scattered for the remainder of the weekend. Showers look to become
numerous again early next week as the NET interacts with a series of
trade-wind troughs. To the northeast, partly cloudy skies and
isolated showers are seen over Yap Proper, where CIMMS MIMIC TPW
shows relatively drier air with PWATs around 1.8 to 1.9 inches. Yap
will remain in this drier pattern for the next day or so before a
series of troughs bring increased showers on Sunday through early
next week.

To the east, scattered to numerous showers are seen to the south of
Weno, Chuuk, associated with the far western periphery of the ITCZ.
This surface convergence and associated convection looks to lift a
bit further north over the next day or so, maintaining scattered
showers over the area through at least Saturday, before a relatively
quieter period on Sunday. A series of trade-wind troughs will bring
on-and-off scattered showers for Chuuk for much of next week.

Latest altimetry shows combined seas of around 3 to 5 feet near Palau
and 4 to 6 feet near Chuuk. These conditions will continue through
the weekend with seas coming down by a foot or so early next week as
wind waves and swells diminish. Winds will be moderate to fresh near
Yap for tonight, coming down to gentle to moderate through early next
week. Trades will be gentle to moderate for Palau, but some stronger
gusts can be expected tonight and tomorrow morning with numerous
showers in the area. Near Chuuk, winds will be gentle to moderate,
becoming moderate to fresh Sunday into early next week.

&&

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

$$

Marianas Update: Williams
East/West Micronesia Update: Doll
Marianas: Bowsher
East Micronesia: Montvila
West Micronesia: DeCou